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Solder
Solder
Solder
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Solder, drawn out to a diameter of 1.6 mm and wound/bent around a spool
A soldered joint used to attach a wire to a through-pin of a component on the rear of a printed circuit board (not a customary application of such joints)

Solder (UK: /ˈsɒldə, ˈsəʊldə/;[1] NA: /ˈsɒdər/)[2] is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable for use as solder should have a lower melting point than the pieces to be joined. The solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder used in making electrical connections also needs to have favorable electrical characteristics.

Soft solder typically has a melting point range of 90 to 450 °C (190 to 840 °F; 360 to 720 K),[3] and is commonly used in electronics, plumbing, and sheet metal work. Alloys that melt between 180 and 190 °C (360 and 370 °F; 450 and 460 K) are the most commonly used. Soldering performed using alloys with a melting point above 450 °C (840 °F; 720 K) is called "hard soldering", "silver soldering", or brazing.

In specific proportions, some alloys are eutectic — that is, the alloy's melting point is the lowest possible for a mixture of those components, and coincides with the freezing point. Non-eutectic alloys can have markedly different solidus and liquidus temperatures, as they have distinct liquid and solid transitions. Non-eutectic mixtures often exist as a paste of solid particles in a melted matrix of the lower-melting phase as they approach high enough temperatures. In electrical work, if the joint is disturbed while in this "pasty" state before it fully solidifies, a poor electrical connection may result; use of eutectic solder reduces this problem. The pasty state of a non-eutectic solder can be exploited in plumbing, as it allows molding of the solder during cooling, e.g. for ensuring watertight joint of pipes, resulting in a so-called "wiped joint".

For electrical and electronics work, solder wire is available in a range of thicknesses for hand-soldering (manual soldering is performed using a soldering iron or soldering gun), and with cores containing flux. It is also available as a room temperature paste, as a preformed foil shaped to match the workpiece which may be more suited for mechanized mass-production, or in small "tabs" that can be wrapped around the joint and melted with a flame where an iron isn't usable or available, as for instance in field repairs. Alloys of lead and tin were commonly used in the past and are still available; they are particularly convenient for hand-soldering. Lead-free solders have been increasing in use due to regulatory requirements plus the health and environmental benefits of avoiding lead-based electronic components. They are almost exclusively used today in consumer electronics.[4]

Plumbers often use bars of solder, much thicker than the wire used for electrical applications, and apply flux separately; many plumbing-suitable soldering fluxes are too corrosive (or conductive) to be used in electrical or electronic work. Jewelers often use solder in thin sheets, which they cut into snippets.

Etymology

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The word solder comes from the Middle English word soudur, via Old French solduree and soulder, from the Latin solidare, meaning "to make solid".[5]

Composition

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Lead-based

[edit]

Sn60Pb40 solder

Tin-lead (Sn-Pb) solders, also called soft solders, are commercially available with tin concentrations between 5% and 70% by weight. The greater the tin concentration, the greater the solder's tensile and shear strengths. Lead mitigates the formation of tin whiskers,[6] though the precise mechanism for this is unknown.[7] Today, many techniques are used to mitigate the problem, including changes to the annealing process (heating and cooling), addition of elements like copper and nickel, and the application of conformal coatings.[8] Alloys commonly used for electrical soldering are 60/40 Sn-Pb, which melts at 188 °C (370 °F),[9] and 63/37 Sn-Pb used principally in electrical/electronic work. The latter mixture is a eutectic alloy of these metals, which:

  1. has the lowest melting point (183 °C or 361 °F) of all the tin-lead alloys; and
  2. the melting point is truly a point — not a range.

In the United States, since 1974, lead is prohibited in solder and flux in plumbing applications for drinking water use, per the Safe Drinking Water Act.[10] Historically, a higher proportion of lead was used, commonly 50/50. This had the advantage of making the alloy solidify more slowly. With the pipes being physically fitted together before soldering, the solder could be wiped over the joint to ensure water tightness. Although lead water pipes were displaced by copper when the significance of lead poisoning began to be fully appreciated, lead solder was still used until the 1980s because it was thought that the amount of lead that could leach into water from the solder was negligible from a properly soldered joint. The electrochemical couple of copper and lead promotes corrosion of the lead and tin. Tin, however, is protected by insoluble oxide. Since even small amounts of lead have been found detrimental to health as a potent neurotoxin,[11] lead in plumbing solder was replaced by silver (food-grade applications) or antimony, with copper often added, and the proportion of tin was increased (see lead-free solder).

The addition of tin—more expensive than lead—improves wetting properties of the alloy; lead itself has poor wetting characteristics. High-tin tin-lead alloys have limited use as the workability range can be provided by a cheaper high-lead alloy.[12]

Lead-tin solders readily dissolve gold plating and form brittle intermetallics.[13] 60/40 Sn-Pb solder oxidizes on the surface, forming a complex 4-layer structure: tin(IV) oxide on the surface, below it a layer of tin(II) oxide with finely dispersed lead, followed by a layer of tin(II) oxide with finely dispersed tin and lead, and the solder alloy itself underneath.[14]

Lead, and to some degree tin, as used in solder contains small but significant amounts of radioisotope impurities. Radioisotopes undergoing alpha decay are a concern due to their tendency to cause soft errors. Polonium-210 is especially troublesome; lead-210 beta decays to bismuth-210 which then beta decays to polonium-210, an intense emitter of alpha particles. Uranium-238 and thorium-232 are other significant contaminants of alloys of lead.[15][16]

Lead-free

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Pure tin solder wire
Soldering copper pipes using a propane torch and lead-free solder

The European Union Waste Electrical and Electronic Equipment Directive and Restriction of Hazardous Substances Directive were adopted in early 2003 and came into effect on July 1, 2006, restricting the inclusion of lead in most consumer electronics sold in the EU, and having a broad effect on consumer electronics sold worldwide. In the US, manufacturers may receive tax benefits by reducing the use of lead-based solder. Lead-free solders in commercial use may contain tin, copper, silver, bismuth, indium, zinc, antimony, and traces of other metals. Most lead-free replacements for conventional 60/40 and 63/37 Sn-Pb solder have melting points from 50 to 200 °C higher,[17] though there are also solders with much lower melting points. Lead-free solder typically requires around 2% flux by mass for adequate wetting ability.[18]

When lead-free solder is used in wave soldering, a slightly modified solder pot may be desirable (e.g. titanium liners or impellers) to reduce maintenance cost due to increased tin-scavenging of high-tin solder.

Lead-free solder is prohibited in critical applications, such as aerospace, military and medical projects, because joints are likely to suffer from metal fatigue failure under stress (such as that from thermal expansion and contraction). Although this is a property that conventional leaded solder possesses as well (like any metal), the point at which stress fatigue will usually occur in leaded solder is substantially above the level of stresses normally encountered.

Tin-silver-copper (Sn-Ag-Cu, or SAC) solders are used by two-thirds of Japanese manufacturers for reflow and wave soldering, and by about 75% of companies for hand soldering. The widespread use of this popular lead-free solder alloy family is based on the reduced melting point of the Sn-Ag-Cu ternary eutectic behavior (217 °C; 423 °F), which is below the 22/78 Sn-Ag (wt.%) eutectic of 221 °C (430 °F) and the 99.3/0.7 Sn-Cu eutectic of 227 °C (441 °F).[19] The ternary eutectic behavior of Sn-Ag-Cu and its application for electronics assembly was discovered (and patented) by a team of researchers from Ames Laboratory, Iowa State University, and from Sandia National Laboratories-Albuquerque.

Much recent research has focused on the addition of a fourth element to Sn-Ag-Cu solder, in order to provide compatibility for the reduced cooling rate of solder sphere reflow for assembly of ball grid arrays. Examples of these four-element compositions are 18/64/14/4 tin-silver-copper-zinc (Sn-Ag-Cu-Zn) (melting range 217–220 °C) and 18/64/16/2 tin-silver-copper-manganese (Sn-Ag-Cu-Mn; melting range of 211–215 °C).

Tin-based solders readily dissolve gold, forming brittle intermetallic joins; for Sn-Pb alloys the critical concentration of gold to embrittle the joint is about 4%. Indium-rich solders (usually indium-lead) are more suitable for soldering thicker gold layers as the dissolution rate of gold in indium is much slower. Tin-rich solders also readily dissolve silver; for soldering silver metallization or surfaces, alloys with addition of silver are suitable; tin-free alloys are also a choice, though their wetting ability is poorer. If the soldering time is long enough to form the intermetallics, the tin surface of a joint soldered to gold is very dull.[13]

Hard solder

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Silver solders (Ag/Cu/Zn) marked with their different hardness. From no.1="repair" to no.5="enameling".
Gold solders (Au/Ag/Cu/Zn) marked with their different hardness. From no.1=lowest temp to no.3=highest temp.

Hard solders are used for brazing, and melt at higher temperatures. Alloys of copper with either zinc or silver are the most common.

In silversmithing or jewelry making, special hard solders are used that will pass assay. They contain a high proportion of the metal being soldered and lead is not used in these alloys. These solders vary in hardness, designated as "enameling", "hard", "medium", "easy" and "repair". Enameling solder has a high melting point, close to that of the material itself, to prevent the joint desoldering during firing in the enameling process. The remaining solder types are used in decreasing order of hardness during the process of making an item, to prevent a previously soldered seam or joint desoldering while additional sites are soldered. Easy solder or repair solder are also often used for repair work for the same reason. Flux is also used to prevent joints from desoldering.

Silver solder is also used in manufacturing to join metal parts that cannot be welded. The alloys used for these purposes contain a high proportion of silver (up to 40%), and may also contain cadmium.

Alloys

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Main article: Solder alloys

Different elements serve different roles in the solder alloy:

  • Antimony is added to increase strength without affecting wettability. Prevents tin pest. Should be avoided on zinc, cadmium, or galvanized metals as the resulting joint is brittle.[20]
  • Bismuth significantly lowers the melting point and improves wettability. In presence of sufficient lead and tin, bismuth forms crystals of Sn16Pb32Bi52 with melting point of only 95 °C, which diffuses along the grain boundaries and may cause a joint failure at relatively low temperatures. A high-power part pre-tinned with an alloy of lead can therefore desolder under load when soldered with a bismuth-containing solder. Such joints are also prone to cracking. Alloys with more than 47% Bi expand upon cooling, which may be used to offset thermal expansion mismatch stresses. Retards growth of tin whiskers. Relatively expensive, limited availability.
  • Copper improves resistance to thermal cycle fatigue, and improves wetting properties of the molten solder. It also slows down the rate of dissolution of copper from the board and part leads in the liquid solder. Copper in solders forms intermetallic compounds. Supersaturated (by about 1%) solution of copper in tin may be employed to inhibit dissolution of thin-film under-bump metallization of BGA chips, e.g. as Sn94Ag3Cu3.[19][21]
  • Nickel can be added to the solder alloy to form a supersaturated solution to inhibit dissolution of thin-film under-bump metallization.[21] In tin-copper alloys, small addition of Ni (<0.5 wt%) inhibits the formation of voids and interdiffusion of Cu and Sn elements.[19] Inhibits copper dissolution, even more in synergy with bismuth. Nickel presence stabilizes the copper-tin intermetallics, inhibits growth of pro-eutectic β-tin dendrites (and therefore increases fluidity near the melting point of copper-tin eutectic), promotes shiny bright surface after solidification, inhibits surface cracking at cooling; such alloys are called "nickel-modified" or "nickel-stabilized". Small amounts increase melt fluidity, most at 0.06%.[22] Suboptimal amounts may be used to avoid patent issues. Fluidity reduction increase hole filling and mitigates bridging and icicles.
  • Cobalt is used instead of nickel to avoid patent issues in improving fluidity. Does not stabilize intermetallic growths in solid alloy.
  • Indium lowers the melting point and improves ductility. In presence of lead it forms a ternary compound that undergoes phase change at 114 °C. Very high cost (several times of silver), low availability. Easily oxidizes, which causes problems for repairs and reworks, especially when oxide-removing flux cannot be used, e.g. during GaAs die attachment. Indium alloys are used for cryogenic applications, and for soldering gold as gold dissolves in indium much less than in tin. Indium can also solder many nonmetals (e.g. glass, mica, alumina, magnesia, titania, zirconia, porcelain, brick, concrete, and marble). Prone to diffusion into semiconductors and cause undesired doping. At elevated temperatures easily diffuses through metals. Low vapor pressure, suitable for use in vacuum systems. Forms brittle intermetallics with gold; indium-rich solders on thick gold are unreliable. Indium-based solders are prone to corrosion, especially in presence of chloride ions.[23]
  • Lead is inexpensive and has suitable properties. Worse wetting than tin. Toxic, being phased out. Retards growth of tin whiskers, inhibits tin pest. Lowers solubility of copper and other metals in tin.
  • Silver provides mechanical strength, but has worse ductility than lead. In absence of lead, it improves resistance to fatigue from thermal cycles. Using SnAg solders with HASL-SnPb-coated leads forms SnPb36Ag2 phase with melting point at 179 °C, which moves to the board-solder interface, solidifies last, and separates from the board.[17] Addition of silver to tin significantly lowers solubility of silver coatings in the tin phase. In eutectic tin-silver (3.5% Ag) alloy and similar alloys (e.g. SAC305) it tends to form platelets of Ag3Sn, which, if formed near a high-stress spot, may serve as initiating sites for cracks and cause poor shock and drop performance; silver content needs to be kept below 3% to inhibit such problems.[21] High ion mobility, tends to migrate and form short circuits at high humidity under DC bias. Promotes corrosion of solder pots, increases dross formation.
  • Tin is the usual main structural metal of the alloy. It has good strength and wetting. On its own it is prone to tin pest and growth of tin whiskers. Readily dissolves silver, gold and to less but still significant extent many other metals, e.g. copper; this is a particular concern for tin-rich alloys with higher melting points and reflow temperatures.
  • Zinc lowers the melting point and is low-cost. However, it is highly susceptible to corrosion and oxidation in air, therefore zinc-containing alloys are unsuitable for some purposes, e.g. wave soldering, and zinc-containing solder pastes have shorter shelf life than zinc-free. Can form brittle Cu-Zn intermetallic layers in contact with copper. Readily oxidizes which impairs wetting, requires a suitable flux.
  • Germanium in tin-based lead-free solders influences formation of oxides; at below 0.002% it increases formation of oxides. Optimal concentration for suppressing oxidation is at 0.005%.[24] Used in e.g. Sn100C alloy. Patented.
  • Rare-earth elements, when added in small amounts, refine the matrix structure in tin-copper alloys by segregating impurities at the grain boundaries. However, excessive addition results in the formation of tin whiskers; it also results in spurious rare earth phases, which easily oxidize and deteriorate the solder properties.[19]
  • Phosphorus is used as antioxidant to inhibit dross formation. Decreases fluidity of tin-copper alloys.

Impurities

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Impurities usually enter the solder reservoir by dissolving the metals present in the assemblies being soldered. Dissolving of process equipment is not common as the materials are usually chosen to be insoluble in solder.[25]

  • Aluminium – little solubility, causes sluggishness of solder and dull gritty appearance due to formation of oxides. Addition of antimony to solders forms Al-Sb intermetallics that are segregated into dross. Promotes embrittlement.
  • Antimony – added intentionally, up to 0.3% improves wetting, larger amounts slowly degrade wetting. Increases melting point.
  • Arsenic – forms thin intermetallics with adverse effects on mechanical properties, causes dewetting of brass surfaces
  • Cadmium – causes sluggishness of solder, forms oxides and tarnishes
  • Copper – most common contaminant, forms needle-shaped intermetallics, causes sluggishness of solders, grittiness of alloys, decreased wetting
  • Gold – easily dissolves, forms brittle intermetallics, contamination above 0.5% causes sluggishness and decreases wetting. Lowers melting point of tin-based solders. Higher-tin alloys can absorb more gold without embrittlement.[26]
  • Iron – forms intermetallics, causes grittiness, but rate of dissolution is very low; readily dissolves in lead-tin above 427 °C.[13]
  • Lead – causes Restriction of Hazardous Substances Directive compliance problems at above 0.1%. Can cause joint failure in bismuth-based solders.
  • Nickel – causes grittiness, very little solubility in Sn-Pb
  • Phosphorus – forms tin and lead phosphides, causes grittiness and dewetting, present in electroless nickel plating
  • Silver – often added intentionally, in high amounts forms intermetallics that cause grittiness and formation of pimples on the solder surface, potential for embrittlement
  • Sulfur – forms lead and tin sulfides, causes dewetting
  • Zinc – in melt forms excessive dross, in solidified joints rapidly oxidizes on the surface; zinc oxide is insoluble in fluxes, impairing repairability; copper and nickel barrier layers may be needed when soldering brass to prevent zinc migration to the surface; potential for embrittlement

Board finishes vs wave soldering bath impurities buildup:

  • HASL, lead-free (Hot Air Level): usually virtually pure tin. Does not contaminate high-tin baths.
  • HASL, leaded: some lead dissolves into the bath
  • ENIG (Electroless Nickel Immersion Gold): typically 100-200 microinches of nickel with 3-5 microinches of gold on top. Some gold dissolves into the bath, but limits exceeding buildup is rare.
  • Immersion silver: typically 10–15 microinches of silver. Some dissolves into the bath, limits exceeding buildup is rare.
  • Immersion tin: does not contaminate high-tin baths.
  • OSP (Organic solderability preservative): usually imidazole-class compounds forming a thin layer on the copper surface. Copper readily dissolves in high-tin baths.[27]

Flux

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Electrical solder with an integrated rosin core, visible as a dark spot in the cut end of the solder wire.
Main article: Flux (metallurgy)

Flux is a reducing agent designed to help reduce (return oxidized metals to their metallic state) metal oxides at the points of contact to improve the electrical connection and mechanical strength. The two principal types of flux are acid flux (sometimes called "active flux"), containing strong acids, used for metal mending and plumbing, and rosin flux (sometimes called "passive flux"), used in electronics. Rosin flux comes in a variety of "activities", corresponding roughly to the speed and effectiveness of the organic acid components of the rosin in dissolving metallic surface oxides, and consequently the corrosiveness of the flux residue.

Due to concerns over atmospheric pollution and hazardous waste disposal, the electronics industry has been gradually shifting from rosin flux to water-soluble flux, which can be removed with deionized water and detergent, instead of hydrocarbon solvents. Water-soluble fluxes are generally more conductive than traditionally used electrical / electronic fluxes and so have more potential for electrically interacting with a circuit; in general it is important to remove their traces after soldering. Some rosin type flux traces likewise should be removed, and for the same reason.

In contrast to using traditional bars or coiled wires of all-metal solder and manually applying flux to the parts being joined, much hand soldering since the mid-20th century has used flux-core solder. This is manufactured as a coiled wire of solder, with one or more continuous bodies of inorganic acid or rosin flux embedded lengthwise inside it. As the solder melts onto the joint, it frees the flux and releases that on it as well.

Operation

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The solidifying behavior depends on the alloy composition. Pure metals solidify at a certain temperature, forming crystals of one phase. Eutectic alloys also solidify at a single temperature, all components precipitating simultaneously in so-called coupled growth. Non-eutectic compositions on cooling start to first precipitate the non-eutectic phase; dendrites when it is a metal, large crystals when it is an intermetallic compound. Such a mixture of solid particles in a molten eutectic is referred to as a mushy state. Even a relatively small proportion of solids in the liquid can dramatically lower its fluidity.[28]

The temperature of total solidification is the solidus of the alloy, the temperature at which all components are molten is the liquidus.

The mushy state is desired where a degree of plasticity is beneficial for creating the joint, allowing filling larger gaps or being wiped over the joint (e.g. when soldering pipes). In hand soldering of electronics it may be detrimental as the joint may appear solidified while it is not yet. Premature handling of such joint then disrupts its internal structure and leads to compromised mechanical integrity.

Intermetallics

[edit]

Many different intermetallic compounds are formed during solidifying of solders and during their reactions with the soldered surfaces.[25] The intermetallics form distinct phases, usually as inclusions in a ductile solid solution matrix, but also can form the matrix itself with metal inclusions or form crystalline matter with different intermetallics. Intermetallics are often hard and brittle. Finely distributed intermetallics in a ductile matrix yield a hard alloy while coarse structure gives a softer alloy. A range of intermetallics often forms between the metal and the solder, with increasing proportion of the metal; e.g. forming a structure of Cu−Cu3Sn−Cu6Sn5−Sn. Layers of intermetallics can form between the solder and the soldered material. These layers may cause mechanical reliability weakening and brittleness, increased electrical resistance, or electromigration and formation of voids. The gold-tin intermetallics layer is responsible for poor mechanical reliability of tin-soldered gold-plated surfaces where the gold plating did not completely dissolve in the solder.

Two processes play a role in a solder joint formation: interaction between the substrate and molten solder, and solid-state growth of intermetallic compounds. The base metal dissolves in the molten solder in an amount depending on its solubility in the solder. The active constituent of the solder reacts with the base metal with a rate dependent on the solubility of the active constituents in the base metal. The solid-state reactions are more complex – the formation of intermetallics can be inhibited by changing the composition of the base metal or the solder alloy, or by using a suitable barrier layer to inhibit diffusion of the metals.[29]

Some example interactions include:

  • Gold and palladium readily dissolve in solders. Copper and nickel tend to form intermetallic layers during normal soldering profiles. Indium forms intermetallics as well.
  • Indium-gold intermetallics are brittle and occupy about 4 times more volume than the original gold. Bonding wires are especially susceptible to indium attack. Such intermetallic growth, together with thermal cycling, can lead to failure of the bonding wires.[30]
  • Copper plated with nickel and gold is often used. The thin gold layer facilitates good solderability of nickel as it protects the nickel from oxidation; the layer has to be thin enough to rapidly and completely dissolve so bare nickel is exposed to the solder.[16]
  • Lead-tin solder layers on copper leads can form copper-tin intermetallic layers; the solder alloy is then locally depleted of tin and form a lead-rich layer. The Sn-Cu intermetallics then can get exposed to oxidation, resulting in impaired solderability.[31]
  • Cu6Sn5 – common on solder-copper interface, forms preferentially when excess of tin is available; in presence of nickel, (Cu,Ni)6Sn5 compound can be formed[19][6]
  • Cu3Sn – common on solder-copper interface, forms preferentially when excess of copper is available, more thermally stable than Cu6Sn5, often present when higher-temperature soldering occurred[19][6]
  • Ni3Sn4 – common on solder-nickel interface[19][6]
  • FeSn2 – very slow formation
  • Ag3Sn - at higher concentration of silver (over 3%) in tin forms platelets that can serve as crack initiation sites.
  • AuSn4 – β-phase – brittle, forms at excess of tin. Detrimental to properties of tin-based solders to gold-plated layers.
  • AuIn2 – forms on the boundary between gold and indium-lead solder, acts as a barrier against further dissolution of gold
Matrix of intermetallic solder compounds
Tin Lead Indium
Copper Cu4Sn, Cu6Sn5, Cu3Sn, Cu3Sn8[19] Cu3In, Cu9In4
Nickel Ni3Sn, Ni3Sn2, Ni3Sn4 NiSn3 Ni3In, NiIn Ni2In3, Ni3In7
Iron FeSn, FeSn2
Indium In3Sn, InSn4 In3Pb –
Antimony SbSn
Bismuth BiPb3
Silver Ag6Sn, Ag3Sn Ag3In, AgIn2
Gold Au5Sn, AuSn AuSn2, AuSn4 Au2Pb, AuPb2 AuIn, AuIn2
Palladium Pd3Sn, Pd2Sn, Pd3Sn2, PdSn, PdSn2, PdSn4 Pd3In, Pd2In, PdIn, Pd2In3
Platinum Pt3Sn, Pt2Sn, PtSn, Pt2Sn3, PtSn2, PtSn4 Pt3Pb, PtPb PtPb4 Pt2In3, PtIn2, Pt3In7

Preform

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A preform is a pre-made shape of solder specially designed for the application where it is to be used. Many methods are used to manufacture the solder preform, stamping being the most common. The solder preform may include the solder flux needed for the soldering process. This can be an internal flux, inside the solder preform, or external, with the solder preform coated.

Similar substances

[edit]

Glass solder is used to join glasses to other glasses, ceramics, metals, semiconductors, mica, and other materials, in a process called glass frit bonding. The glass solder has to flow and wet the soldered surfaces well below the temperature where deformation or degradation of either of the joined materials or nearby structures (e.g., metallization layers on chips or ceramic substrates) occurs. The usual temperature of achieving flowing and wetting is between 450 and 550 °C (840 and 1,020 °F).

See also

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Solder

View on Grokipedia
from Grokipedia

Solder is a fusible metal , typically with a below 450°C (840°F), employed to join metallic surfaces by the to wet the and subsequently solidifying it without melting the base materials.
Historically utilized since at least 3000 BCE in Sumerian assemblies, solder has enabled durable connections in applications from ancient artifacts to contemporary , , and components.
Traditional formulations, such as eutectic 63% tin-37% lead, offered low points around 183°C and reliable , but lead's prompted regulatory shifts, including the EU RoHS directive effective 2006, mandating lead-free alternatives like SAC305 (96.5% tin, 3% silver, 0.5% ) with points of 217–220°C.
These lead-free alloys, while environmentally preferable, introduce challenges including higher processing temperatures, increased brittleness, and risks like tin whisker growth, which can compromise long-term reliability in demanding environments such as vibration-prone or thermally cycled assemblies.
processes incorporate to remove oxides and promote adhesion, with techniques spanning manual irons for prototyping to automated reflow ovens for high-volume production.

Historical Development

Ancient Origins and Early Applications

Archaeological and metallurgical evidence indicates that soldering originated in the , with the earliest documented applications around 3000 BCE in , where craftsmen employed soft solders—likely natural lead-tin s—to join gold and silver for jewelry and decorative artifacts. This technique involved heating a lower-melting to form a metallurgical bond with the base material, enabling durable connections without the high temperatures required for fusion that could distort delicate work. Sumerian artisans, in particular, utilized these methods to assemble intricate pieces, demonstrating an understanding of compositions that provided mechanical strength through and formation. Similar practices emerged contemporaneously in , where soldering facilitated the creation of ornate metalwork, including amulets and vessels, often incorporating lead-tin solders for their flux-like properties and ease of application via simple torches or fires. The technique's utility lay in its ability to produce leak-proof and structurally sound joints, causal to the production of complex, non-malleable assemblies that exceeded the limits of hammering or riveting alone. By the , these methods spread through trade and cultural exchange across the Mediterranean, from Minoan to Etruscan , adapting to local materials while preserving of differential melting points for reliable . In Roman applications, advanced practical engineering, particularly in systems where lead pipes—joined with lead-tin solder—formed extensive networks spanning over 400 kilometers in cities like , ensuring watertight seals for aqueduct distribution. This innovation, inherited via Etruscan intermediaries, underscored 's role in enabling scalable infrastructure, as the process allowed field repairs and expansions with minimal equipment, relying on the solder's flow to fill gaps and create corrosion-resistant bonds essential for long-term hydraulic functionality.

Industrial and Electronic Advancements

Soldering emerged as a critical technique in the early 19th century for assembling telegraph systems and nascent electrical devices, where tin-lead alloys facilitated durable, low-resistance joints capable of handling increasing electrical currents for signal transmission. These alloys, typically composed of 60% tin and 40% lead, offered a eutectic mixture with a melting point around 183°C, enabling quick formation of intermetallic bonds that enhanced conductivity and mechanical strength against vibration in wire connections. Following , soldering advanced significantly during the 1940s-1960s electronics expansion, driven by the transistor's invention in 1947 and the mass production of printed circuit boards (PCBs), which shifted from hand-soldered point-to-point wiring to automated methods like dip and early for scalable assembly. Solder preforms, precision-shaped alloy pieces, gained prominence in high-reliability applications, including the initial missiles developed in the 1970s, where they ensured consistent hermetic seals and thermal management in defense electronics under extreme conditions. These developments improved joint reliability by minimizing voids and promoting uniform wetting, directly supporting higher circuit densities and in military and consumer devices. From the 1980s to the 2000s, the adoption of (SMT), originating in the but proliferating with demands, integrated processes using or ovens to melt on PCBs, enabling component placement directly on board surfaces without through-holes. This shift reduced parasitic and , enhancing electrical performance and conductivity in high-frequency like computers and mobile devices, while reflow profiles optimized for tin-lead alloys achieved void-free joints exceeding 95% yield in production. SMT's scalability addressed reliability challenges in dense assemblies by allowing automated placement and inspection, causal to the industry's growth in portability and performance.

Etymology and Terminology

Origins of the Term

The English term "solder" originates from soudur or souder, denoting a fusible used to join metals by and solidifying. This form entered the around the via Anglo-French and souldure or soudeure, derived from the verb souder, which signified the act of fastening or consolidating materials. The root traces directly to Latin solidare, meaning "to make solid" or "to fasten together," from solidus, denoting something firm or unyielding. This etymological path underscores the empirical function of the process: achieving a durable, unified through fusion and cooling, independent of specific alloys or techniques. The spelling's retention of the 'l'—absent in some modern pronunciations like "sodder"—preserves the Latin influence, distinguishing it from phonetic drifts in . Early usages in technical texts, such as 15th-century English treatises on , applied the term to lead-tin mixtures valued for their low melting points and bonding reliability. Soldering is distinguished from related metal-joining processes primarily by the melting temperature of the filler material, which is defined as below 450°C (842°F) according to standards from the American Welding Society (AWS) and the Society of Automotive Engineers (SAE). Within soldering, soft solders typically melt below °C, enabling applications sensitive to , while hard solders melt between °C and 450°C. In contrast, employs filler metals that melt above 450°C but below the of the base materials, and requires heating the base metals themselves to their melting points, often exceeding 1000°C depending on the . Causally, soldering forms a through , where the molten filler wets and flows into the prepared gap between closely fitted components via , followed by limited interdiffusion at the interface to create a metallurgical bond without liquefying the s. This avoids the thermal distortion and microstructural changes associated with base metal melting in , which fuses the parts through solidification of a molten pool that mixes base and filler materials. shares soldering's reliance on capillary flow and non-melting of bases but at higher temperatures, yielding stronger bonds due to greater and . These distinctions enable soldering's precision in low-heat scenarios, such as assembly, where temperatures around 200-250°C prevent warping of printed circuit boards or degradation of semiconductors, as evidenced by joint shear strengths typically below 50 MPa suited for electrical conductivity rather than structural loads. , by comparison, supports higher-strength applications like in systems, with joint strengths up to 200 MPa and better resistance to vibration, while provides the highest integrity for load-bearing structures but risks weakening.

Properties and Classification

Physical and Thermal Properties

Solders typically exhibit densities in the range of 7 to 11 g/cm³, with lead-containing alloys such as the Sn-37Pb eutectic reaching approximately 8.4 g/cm³, while lead-free variants like Sn-Ag-Cu tend toward the lower end around 7.3 to 7.5 g/cm³. This variation arises from the atomic masses and structures of constituent elements, influencing and mechanical loading in applications. Tensile strengths for soft solders, such as the Sn-37Pb eutectic, generally fall between 20 and 50 MPa, with enabling elongation before fracture, which contributes to resistance under cyclic stresses. Thermal properties critically determine joint integrity through phase transitions and mismatch with base materials. Eutectic compositions like Sn-63Pb-37 exhibit sharp melting points at 183°C, facilitating uniform and minimizing voids, whereas non-eutectic alloys display broader solidus-liquidus ranges that can affect flow control. Coefficients of thermal expansion (CTE) for common solders range from 20 to 30 ppm/°C, with Sn-Pb eutectic at approximately 24-25 ppm/°C; discrepancies with substrates like (17 ppm/°C) induce shear stresses during cycling, potentially leading to cracks via thermomechanical . Wettability, governed by and quantified by measurements, ensures proper spreading and ; angles below 90° indicate favorable on clean metal surfaces, promoting flow into joints, while higher angles signal poor adherence due to barriers or inadequacy. conductivities around 50 W/m·K for Sn-Pb alloys support heat dissipation in electronic assemblies, though lower than pure metals like (400 W/m·K), necessitating design considerations for . Electrical conductivity, with resistivities on the order of 150-200 µΩ·cm, suffices for low-resistance joints but is inferior to base conductors, emphasizing the role of minimal joint volume in .

Soft Versus Hard Solders

Soft solders are defined by their low melting temperatures, typically below 450°C, enabling applications requiring minimal on base materials. Common alloys include tin-lead eutectics, such as 60/40 Sn-Pb, which melt around 183°C and provide good for accommodating minor mechanical deformations without fracturing. These solders exhibit shear strengths generally under 50 MPa, prioritizing flowability and over ultimate load-bearing capacity, which suits low-vibration environments but limits use in high-stress scenarios due to reduced resistance to creep under sustained loads. In contrast, hard solders melt between 450°C and approximately 800°C, demanding higher process temperatures that enhance integrity through greater metallurgical bonding but increase risks of base metal distortion or oxidation without adequate protection. Alloys like silver-copper or silver-based variants offer superior creep resistance and shear strengths exceeding 100 MPa, making them suitable for demanding conditions such as components subject to and . This classification aligns with standards like DIN ISO 857-2, which delineate from by filler metal liquidus temperature, ensuring hard solders remain distinct from higher-melting braze fillers while avoiding confusion in process selection. The primary causal trade-off lies in performance thresholds: soft solders facilitate rapid, low-energy joining with inherent compliance, but their lower homologous temperature margin (strength loss above 75% of ) compromises long-term durability under load; hard solders invert this by prioritizing shear and endurance at the expense of process complexity and input.
PropertySoft Solder (e.g., Sn-Pb)Hard Solder (e.g., Ag-Cu)
Melting Range<450°C450–800°C
Typical Shear Strength<50 MPa>100 MPa
Key Advantage, ease of applicationCreep resistance, tolerance
Empirical ThresholdLow-stress, -orientedHigh-stress, structural

Composition and Alloys

Lead-Based Alloys

The eutectic alloy Sn63Pb37, consisting of 63% tin and 37% lead by weight, melts at a precise of °C, enabling sharp melting and freezing without a pasty range for superior joint uniformity and flow characteristics during processes such as surface-mount technology (SMT) and . This composition promotes clean solder joints with high reliability, as the eutectic structure facilitates rapid solidification that minimizes defects like incomplete . The imparted by the lead phase reduces the risk of brittle failures under mechanical stress, contributing to robust interconnections in electronic assemblies. A common variant, Sn60Pb40 with 60% tin and 40% lead, exhibits a range from 183°C solidus to 191°C liquidus, allowing a brief state that accommodates slight misalignments but results in marginally higher voiding potential compared to the eutectic due to prolonged liquidity. This is favored in cost-sensitive applications where tin content reduction lowers material expenses without severely compromising performance, maintaining versatility across electronic and general tasks. Lead-based solders like Sn63Pb37 form a homogeneous microstructure featuring a lead-rich matrix surrounding tin dendrites, which enhances compliance and limits excessive intermetallic compound growth at interfaces, such as slower Cu6Sn5 layer formation relative to tin-dominant alloys. Empirical field performance from electronics manufactured before 2006 demonstrates sustained reliability, with low failure rates attributable to these microstructural traits that resist thermal fatigue and vibration-induced deformation.

Lead-Free Alloys

Lead-free solder alloys, predominantly based on tin with additions of silver and copper, emerged as primary replacements for traditional tin-lead eutectics to mitigate lead's in electronic manufacturing. The most widely adopted composition is SAC305, consisting of 96.5% tin (Sn), 3.0% silver (Ag), and 0.5% copper (Cu) by weight, with a solidus melting point of 217°C and liquidus of 221°C, enabling reliable while requiring higher process temperatures than Sn63Pb37. These alloys demonstrate increased , conferring greater stiffness to joints under mechanical stress, though empirical mechanical testing reveals reduced and propensity for under cyclic loading compared to leaded counterparts. To address cost pressures from silver's market volatility, low-silver variants such as SAC105 (approximately 96.5% Sn, 1.0% Ag, 0.5% Cu) have gained traction, offering comparable resistance and improved drop-shock performance in handheld devices while lowering material expenses without significantly compromising integrity. For applications demanding lower processing temperatures, such as rework or heat-sensitive components, bismuth-tin alloys like Sn42Bi58 provide a eutectic composition with a of 138°C, facilitating easier and reduced thermal damage, though their brittleness limits use in high-strain environments. Trace impurities, including at levels around 100-500 ppm, are empirically incorporated into tin-rich lead-free alloys to suppress tin whisker formation—a spontaneous growth phenomenon that risks electrical shorting—by stabilizing grain boundaries and reducing compressive stresses, as demonstrated in accelerated aging tests showing delayed whisker emergence relative to pure tin. Such micro-alloying enhances long-term reliability metrics without altering bulk melting behavior.

Specialized Alloys and Impurities

Specialized incorporate elevated concentrations of elements like silver or to enhance performance in demanding environments, such as applications requiring superior thermal conductivity and reliability. For instance, tin-silver alloys with approximately 4% silver (SnAg4) exhibit a range around 224–230°C, enabling robust joints under high-stress conditions while maintaining compatibility with lead-free standards. -tin alloys, often used in die-attach and hermetic sealing for in harsh settings, provide exceptional corrosion resistance and thermomechanical stability due to 's nobility and compatibility with formation. Low-melting-point alloys based on , tin, and cater to heat-sensitive components, with eutectic Sn-58Bi melting at 139°C and Sn-In variants as low as 120°C, minimizing thermal damage during assembly of flexible substrates or temperature-vulnerable devices. These formulations reduce peak process temperatures to 170–200°C, preserving integrity in applications like , though they demand careful control to avoid in shear loading. Impurities in critically influence joint integrity, with trace levels altering microstructure and mechanical properties; for example, iron concentrations exceeding 0.1% promote brittle compounds (e.g., FeSn2), reducing as observed in scanning electron (SEM) analyses of boundaries. additions up to 0.2%, per IPC J-STD-006C specifications for electronic-grade alloys, enhance tensile strength by refining structure and inhibiting coarsening, though excesses can embrittle the matrix. Empirical thresholds in J-STD-006 limit impurities like Fe to <0.02–0.05% in high-purity Sn-based alloys to prevent dross formation and ensure wetting, with SEM-verified causal links showing trace dopants (e.g., 0.05% Ni or In) suppressing β-Sn growth and stabilizing intermetallics under thermal cycling.
ImpurityMaximum Allowable Level (J-STD-006C)Effect on Solder Joint
Iron (Fe)<0.02–0.05%Induces brittleness via intermetallic formation; disrupts grain refinement
Antimony (Sb)≤0.2%Improves strength and creep resistance; refines microstructure
Gold (Au)≤0.05%Enhances conductivity but risks embrittlement if excessive

Flux and Joint Preparation

Role and Types of Flux

Flux functions as a chemical cleaning and activating agent in soldering, primarily by removing oxide layers from metal surfaces to enable proper wetting and flow of molten solder. These oxides, formed naturally on metals like copper and tin, impede solder adhesion by increasing surface tension and preventing intermetallic bond formation. Flux achieves oxide removal through reducing reactions or acid-based dissolution, where activators such as organic acids or hydrochloric acid derivatives react to break down the oxide film into soluble compounds. Additionally, flux creates a temporary barrier against atmospheric oxygen, minimizing re-oxidation during the heating phase when temperatures reach 200–400°C. The causal mechanism often involves in-situ generation of hydrochloric acid from precursors like zinc chloride or ammonium chloride, which protonates and dissolves metal oxides via hydrolysis, quantified by reduced contact angles and faster solder spreading. Empirical wetting balance tests demonstrate that flux application can decrease zero-crossing wetting times by 1–5 seconds depending on flux activity and temperature, with activated fluxes showing superior performance over non-activated variants in promoting capillary flow on substrates. This improvement correlates with enhanced joint reliability, as unremoved oxides lead to voids or weak intermetallics. Flux types are categorized by composition, activity level, and residue behavior, with rosin-based fluxes being the mildest, derived from pine resin colophony, offering low corrosivity suitable for electronics where no-clean residues (IPC class ROL0 or ROM0) are permissible post-reflow. Water-soluble fluxes, incorporating aggressive organic acids like adipic or succinic, provide higher activity for heavily oxidized surfaces but necessitate post-soldering cleaning to mitigate residue corrosivity, classified under IPC J-STD-004 as types like WS (e.g., ORH1 for high activity, low solids). Synthetic or activated synthetic fluxes (SA types) employ halide-free or low-halide synthetic resins for high-temperature applications, balancing oxide removal with minimal residue activation per IPC corrosivity tests like SIR (surface insulation resistance) and electrochemical migration assessments. IPC-ANSI J-STD-004 standardizes these via flux activity (L/M/H for low/moderate/high) and residue corrosivity (0/1 for non/low-corrosive), ensuring compatibility with assembly processes through halide content thresholds below 0.05% for "halide-free" designations.

Surface Preparation Techniques

Surface preparation prior to soldering involves removing oxides, contaminants, and residues from base materials to ensure proper solder wetting and adhesion, as unclean surfaces impede intermetallic bond formation. Mechanical methods, such as abrading with emery cloth, steel wool, or brushing, physically disrupt oxide layers on metals like copper, exposing fresh substrate for solder flow. Chemical degreasing uses solvents or alcohol rinses to dissolve organic residues like oils, often combined with mechanical action for thorough oxide reduction. Effective preparation targets minimal oxide thickness, typically below detectable limits post-treatment, to promote uniform solder spreading. For surface-mount technology (SMT) applications, advanced techniques like ultrasonic cleaning employ cavitation in solvent baths to dislodge particles from fine-pitch components without mechanical damage, ensuring residue-free pads. Plasma activation, via ionized gas exposure, etches oxides and activates surfaces at the atomic level, enhancing reactivity for fluxless processes. Wettability is verified by contact angle measurements, where angles below 60° indicate sufficient cleanliness for solder adhesion, as higher values signal persistent barriers to liquid metal flow. Contaminants such as handling oils or plating defects cause dewetting, where solder beads up instead of adhering, leading to joint voids; failure analyses attribute up to 25% of soldering defects to such issues, often traced to oxidized or impure surfaces. In one electronics product study, de-wetting stemmed from contaminated PCB plating, resolved only after rigorous pre-cleaning protocols. These pitfalls underscore the causal link between substrate purity and joint reliability, independent of flux efficacy.

Soldering Processes

Manual and Hand Soldering

Manual soldering employs handheld tools such as temperature-controlled irons or guns to melt solder and form joints in low-volume applications like electronics prototyping and repairs. Soldering iron tips are typically maintained at 300–400°C to achieve rapid solder melting while minimizing thermal stress on components. This range facilitates efficient heat transfer via conduction from the tip to the joint area, with dwell times kept brief to prevent damage such as lead deformation or delamination in sensitive parts. In through-hole assembly, operators insert component leads into plated holes, apply flux, and use techniques like drag soldering—dragging a tinned chisel tip along aligned pins while feeding solder—to create uniform fillets in a single pass. Proper execution ensures solder wets the lead and pad per IPC-A-610 criteria, forming concave fillets with wetting angles under 90° for mechanical integrity. Heat management involves preheating boards judiciously and using heat sinks or tweezers on leads to dissipate excess energy, avoiding overheating that could degrade components. For plumbing, hand torch soldering heats copper pipe fittings with propane or MAPP gas flames to promote capillary flow of solder into joints, targeting even heating on the fitting rather than the pipe to prevent warping. Operators apply flame at a 45° angle until flux bubbles indicate readiness, then introduce solder which melts at 220–230°C for 95/5 tin-antimony alloys, filling the gap via wicking. Manual control allows adaptation to pipe diameters from 1/2 to 2 inches but introduces variability in flame intensity, limiting precision compared to automated methods and necessitating post-solder cleaning to remove flux residues. These techniques rely on operator skill for consistent thermal profiling, with empirical data indicating joint solidification in seconds to balance wetting and avoid intermetallic excess or voids from insufficient heat. Limitations include inconsistent heat distribution in complex geometries, making manual processes ideal for repairs but prone to defects like cold joints without rigorous technique.

Automated and Mass Production Methods

Reflow soldering dominates automated surface-mount technology (SMT) assembly, where PCBs with stencil-printed solder paste and placed components traverse multi-zone conveyor ovens employing forced convection heating to elevate temperatures progressively, culminating in a reflow zone peak of 250–260°C to liquefy lead-free alloys like SAC305 without damaging components. This method ensures uniform heating across high-volume production, with throughput rates scaling to thousands of joints per board in minutes per panel. Wave soldering supports mass production of through-hole and mixed-technology PCBs by fluxing, preheating, and immersing boards over a molten solder pot pumped into turbulent waves, achieving processing speeds of hundreds of boards per hour while maintaining consistent immersion times of 2–5 seconds to form reliable fillet joints. For precision tasks on dense or hybrid boards, selective soldering systems use robotic nozzles to target specific vias or connectors, minimizing thermal stress; the global selective soldering market reached approximately USD 163 million in 2025 projections from 2024 baselines. Laser soldering complements these by delivering focused, non-contact energy densities up to 10^6 W/cm² for micro-joints in electronics, enabling sub-millisecond heating cycles ideal for heat-sensitive devices. Process consistency yields exceed 99% defect-free rates in optimized lines through integration of solder paste inspection (SPI) pre-placement and automated optical inspection (AOI) post-reflow, which detect anomalies like bridging or insufficient paste volume via 3D profilometry and machine vision, correlating upstream data to preempt failures. Employing nitrogen atmospheres in reflow ovens, typically at 1000–5000 ppm oxygen levels, causally suppresses surface oxidation on pads and leads by displacing reactive gases, enhancing wetting and reducing voids by up to 50% compared to air environments. Emerging integrations of AI-driven analytics in robotic soldering stations, announced in 2023 implementations like Samsung's fault detection systems, predict defects via real-time convolutional neural networks analyzing thermal profiles and imagery, achieving 15% accuracy gains and 30% false positive reductions to sustain high-volume reliability.

Joint Formation and Intermetallic Compounds

In solder joints on copper substrates, the formation of a metallurgical bond occurs via the diffusion-driven reaction between liquid tin in the solder and solid copper, primarily yielding the Cu₆Sn₅ intermetallic compound (IMC) at the interface, with Cu₃Sn forming adjacently toward the copper side. This Cu₆Sn₅ layer, typically 1-3 μm thick immediately post-reflow, ensures wetting and adhesion by dissolving surface oxides and establishing atomic-level coherence. The process initiates rapidly during the brief liquid-solid interaction of soldering (seconds to minutes at 220-260°C), where tin atoms migrate outward from the solder bulk, consuming copper to nucleate scalloped Cu₆Sn₅ grains that anchor the joint. Cross-sectional microscopy confirms this layered morphology, with Cu₆Sn₅ dominating due to its lower formation energy compared to Cu₃Sn under liquid-phase conditions. Post-formation growth of IMCs proceeds via solid-state diffusion, following a parabolic rate law (thickness ∝ √t) after initial linear kinetics, driven by concentration gradients and thermally activated vacancy mechanisms. Empirical kinetics reveal strong temperature dependence per the , with activation energies around 0.8-1.2 eV for Cu₆Sn₅ diffusion; for instance, at 150°C aging, layer thickening occurs at rates yielding 2-5 μm after 1000-5000 hours, verifiable through sequential etching and SEM analysis. Causal asymmetry in diffusivities—tin migrating ~10-100 times faster than copper—generates Kirkendall voids within or adjacent to the Cu₃Sn layer, manifesting as sub-micron cavities that nucleate cracks under stress, particularly when total IMC exceeds 8-10 μm, shifting failure from ductile solder to brittle intermetallic fracture. Alloy composition causally modulates these kinetics: Sn-Pb eutectic solders exhibit slower IMC growth (thinner layers by 20-50% under equivalent aging) owing to lead's partitioning that impedes tin flux, preserving higher shear strengths (e.g., 30-50 MPa retention post-aging) versus Sn-Ag-Cu (SAC) alloys, where unalloyed tin promotes rapid thickening and ~10-20% shear degradation from enhanced brittleness. SAC variants form coarser Cu₆Sn₅ grains, accelerating void coalescence via faster grain-boundary diffusion, as quantified in isothermal studies showing SAC layers reaching 5-7 μm in 1000 hours at 125°C compared to 3-4 μm for Sn-Pb. These differences arise from Pb's lattice distortion reducing vacancy mobility, a first-principles effect confirmed by diffusion coefficient measurements, emphasizing composition's role in causal microstructural control for joint longevity.

Applications

Electronics and Circuitry

For manual hand soldering in electronics, such as prototyping and repairs in non-regulated contexts, eutectic 63/37 or 60/40 tin-lead rosin-core solder wire in diameters of 0.8 mm or thinner is commonly recommended for its low melting point around 183°C, sharp solidification, and reliable wetting properties that form strong joints. Solder plays a critical role in electronics by forming electrically conductive and mechanically robust joints between components and printed circuit boards (PCBs), primarily through surface-mount technology (SMT) and ball grid array (BGA) assemblies. In SMT processes, solder paste—typically composed of lead-free alloys—is screen-printed onto PCB pads, components are placed via automated equipment, and the assembly undergoes reflow soldering to melt the paste and create intermetallic bonds that ensure low-resistance electrical connectivity and thermal dissipation. These joints enable the high-density interconnects necessary for modern devices, supporting the continued scaling of electronic systems beyond traditional transistor miniaturization by facilitating compact layouts and multi-layer boards. BGA packages, prevalent in high-performance applications like servers and processors, utilize pre-formed solder balls made from tin-silver-copper (SAC) alloys such as SAC305 or SAC405, which offer higher melting points (around 217–220°C) and better resistance to electromigration compared to eutectic tin-lead solders. The SAC composition provides reliable underfill compatibility and withstands the thermal profiles of lead-free reflow, with billions of such joints produced annually to meet demand for data centers and computing infrastructure, where joint integrity directly impacts system uptime. Thermal cycling from operational power fluctuations and ambient temperature variations poses empirical challenges to solder joint reliability in consumer electronics, inducing fatigue through coefficient of thermal expansion mismatches between components and PCBs. Lead-free SAC joints, while compliant with regulations, exhibit creep and cracking under repeated cycles, with accelerated testing revealing characteristic lives of thousands of cycles equivalent to 10–20 years under moderated consumer conditions, though real-world longevity depends on design margins and usage profiles. Proper alloy selection and process controls mitigate these risks, ensuring solder's foundational contribution to device functionality and extending service life in applications from smartphones to embedded systems.

Plumbing and Structural Uses

In plumbing applications, lead-free solders such as 95/5 tin-antimony (Sn-Sb) alloys are standard for joining copper pipes in potable water systems, ensuring compliance with NSF/ANSI 61 standards for low lead content and safe leaching limits under aqueous conditions. These alloys form reliable capillary joints that maintain hydraulic integrity, withstanding typical residential water pressures of 100-150 psi while resisting corrosion from chlorinated water and scaling. The tin matrix provides inherent oxidation resistance, while the antimony addition enhances tensile strength and fluidity during melting (at 232-240°C), enabling void-free seals critical for leak prevention. Structural uses of solder extend to low-pressure piping in building systems, where ASME B31.3 permits soldered joints only in Category D fluid service (non-flammable, low-hazard fluids at temperatures below 93°C and pressures not exceeding code limits), prioritizing corrosion resistance over high-stress performance. Empirical data from alloy testing shows these joints achieve decades of service in copper plumbing, with tin-based solders demonstrating superior long-term durability in moist environments compared to historical leaded variants, due to reduced galvanic corrosion with copper substrates. However, in hot water lines (up to 60-82°C), creep deformation accelerates under sustained load and thermal exposure, as tin's low melting point (232°C) allows viscous flow over time, contrasting with the fatigue-dominated cycling in ambient electronics applications; antimony mitigates this by increasing rigidity and reducing strain rates. Joint preparation, including flux application and oxy-fuel torches for even heating, is essential to maximize intermetallic bonding and pressure retention, with failures often traced to incomplete wetting rather than alloy inadequacy.

Aerospace and High-Reliability Fields

In aerospace applications, solder joints must endure extreme vibrations, thermal cycling, and mechanical shocks, often tested under MIL-STD-810 Method 514 for vibration to detect failures like cracked joints or chafing. Eutectic SnPb solder has demonstrated superior performance in high-frequency vibration tests compared to lead-free alternatives, with SnPb joints exhibiting fewer electrical failures and better fatigue resistance up to 800 Hz. NASA-DoD evaluations of lead-free SAC alloys in aerospace hardware revealed higher failure rates under combined vibration and thermal stress, prompting exemptions for SnPb in mission-critical systems where reliability trumps RoHS compliance. For high-temperature environments like rocket engines, gold-based alloys such as 80Au-20Sn provide enhanced creep resistance and are used in wire bonding or die attachment, though excessive gold can induce embrittlement via intermetallic formation. To mitigate voids that compromise joint integrity under vibration—potentially exceeding 5% volume and accelerating crack propagation—solder preforms are employed alongside paste, reducing void levels and improving standoff in bottom-terminated components for defense electronics. Empirical data from reliability protocols confirm that such optimizations, combined with legacy SnPb, yield lower defect rates in vibration-survivable assemblies versus mandated lead-free substitutes.

Reliability and Failure Analysis

Common Failure Mechanisms

Thermo-mechanical fatigue represents a primary failure mode in solder joints, driven by differential thermal expansion between the solder alloy and adhered components or substrates during temperature cycling. Coefficient of thermal expansion (CTE) mismatches induce shear stresses that accumulate plastic strain, initiating microcracks at joint peripheries and propagating them through grain boundaries or intermetallic layers, often culminating in open circuits after thousands to millions of cycles under accelerated testing conditions equivalent to 10^6 operational cycles in some environments. Void formation compromises joint reliability by diminishing load-bearing cross-sections and serving as crack nucleation sites under subsequent stresses. These defects arise from flux volatilization or gas entrapment during reflow soldering, where incomplete escape of evolved gases from activating agents creates micro- or macrovoids, particularly in vapor phase or convection reflow profiles; voids exceeding 10-15% of joint volume can reduce fatigue life by up to 50% via localized stress amplification. Electromigration manifests as atomic diffusion under high current densities, forming voids at anode interfaces and hillocks at cathodes, which erode joint continuity; this process accelerates markedly above 100°C due to thermally activated vacancy fluxes, with failure times following Arrhenius kinetics verifiable through accelerated life testing. In high-purity tin-based solders, spontaneous tin whisker growth—filamentary extrusions driven by compressive residual stresses—can bridge circuits, inducing intermittent or catastrophic shorts; documented failures include satellite malfunctions after 4-8 years of dormancy, underscoring long-term reliability risks absent in alloyed variants with stabilizers. Failure distributions in these mechanisms are commonly analyzed using Weibull statistics, where shape parameter β >1 indicates wear-out progression, enabling extrapolation of characteristic life (η) from test data to predict field reliability under thermo-mechanical or electrical loads.

Comparative Reliability of Alloy Types

Eutectic tin-lead (Sn63Pb37) solders demonstrate superior ductility relative to lead-free Sn-Ag-Cu (SAC) alloys such as SAC305 (Sn96.5Ag3Cu0.5), owing to a lower Young's modulus of approximately 30-40 GPa compared to 45-55 GPa for SAC, which contributes to reduced brittleness and better compliance under thermal-mechanical loading. This mechanical advantage in SnPb enables higher fatigue life in scenarios involving large temperature differentials (delta T > 60°C), where SAC joints exhibit accelerated crack propagation due to stiffness. In contrast, SAC alloys provide enhanced creep resistance at room temperature, with strain rates 3-5 times lower than SnPb under low-stress conditions, though this benefit diminishes in high-strain environments. ![60-40 Solder][float-right] The elevated of SAC alloys (217°C) versus SnPb (183°C) requires reflow profiles exceeding 240-260°C peak temperatures, increasing risks of substrate warpage, component , and residual stresses that compromise long-term joint integrity, as evidenced by higher post-assembly defect rates in lead-free assemblies. compound (IMC) growth at the solder-substrate interface proceeds more rapidly in SAC systems, forming thicker Cu6Sn5 and Cu3Sn layers that embrittle joints over time, particularly under isothermal aging or thermal cycling, compared to the slower kinetics in SnPb where lead mitigates excessive IMC buildup. Lead-free SAC solders, with their high tin content (>96%), exhibit greater susceptibility to tin whisker formation than SnPb alloys, where lead acts as an inhibitor; whiskers have precipitated electrical shorts and failures in high-reliability applications, including NASA-documented cases of relay and processor malfunctions in satellites. Empirical field data post-RoHS transition reveal elevated failure incidences in SAC assemblies under vibration and thermal fatigue, attributed to these microstructural vulnerabilities, despite laboratory thermal cycling tests sometimes favoring SAC in controlled, low-delta-T regimes. SnPb's lower processing temperatures also facilitate easier rework and repair, reducing secondary damage risks absent in SAC's higher-heat demands.
PropertyEutectic SnPbSAC305
183°C217°C
(approx.)30-40 GPa45-55 GPa
Creep Resistance (room temp)Lower (baseline)3-5x higher
IMC Growth RateSlowerFaster, thicker layers
Whisker SusceptibilityLow (Pb suppresses)High (pure Sn-like)
This table summarizes key empirical trade-offs, with SnPb excelling in ductility-driven reliability for demanding cyclic loads, while SAC's stiffness aids static creep but amplifies risks in dynamic or whisker-prone environments.

Health, Safety, and Environmental Considerations

Toxicity and Exposure Risks

Solder, particularly lead-containing alloys such as Sn63Pb37, releases lead vapors and particulates during melting and use, contributing to in humans due to slow excretion and storage primarily in bones and soft tissues. Occupational of these fumes can elevate blood lead levels (BLLs), with the Centers for Disease Control and Prevention (CDC) using a blood lead reference value of 3.5 μg/dL to identify elevated exposure associated with neurotoxic effects, including impaired cognitive function and developmental risks in exposed populations. Chronic low-level lead exposure disrupts neurological processes via interference with and , with no safe threshold established for adverse effects. Airborne lead concentrations from soldering fumes typically range from 0.01 to 0.2 mg/m³ in poorly ventilated settings, often approaching or exceeding the (OSHA) permissible exposure limit (PEL) of 0.05 mg/m³ as an 8-hour time-weighted average, leading to verifiable chronic effects such as and renal impairment upon sustained elevation. In contrast, tin and components in exhibit lower systemic ; tin fumes primarily cause respiratory irritation at high concentrations, while poses minimal risks beyond localized effects, though both contribute to overall particulate exposure. Rosin-based fluxes, commonly used in electronics , decompose into sensitizing aldehydes and particulates that can induce through lung , with studies linking fume exposure to and in affected workers. Physical hazards include thermal burns from soldering irons operating at 350–400°C, which can cause second- or third-degree injuries upon contact, and ocular or corneal from molten solder splatter.

Mitigation Practices and Fume Hazards

Local exhaust ventilation systems, positioned close to the soldering site, effectively capture fumes generated from volatilization and metal vapors, preventing their dispersion into the breathing zone. These systems typically require airflow rates of at least 100 cubic feet per minute (CFM) to achieve adequate capture velocities for soldering operations, with empirical evaluations demonstrating substantial reductions in airborne contaminants. For instance, facilities employing local exhaust reported worker exposures to airborne lead well-controlled below occupational limits, contrasting with unventilated setups where concentrations exceeded permissible exposure levels (PELs). OSHA guidelines emphasize source extraction over general dilution ventilation to minimize recirculation of hazardous particulates and gases. Personal protective equipment (PPE) supplements , with NIOSH-approved N95 respirators providing filtration efficiency of at least 95% against non-oil-based particulates like metal fumes from . Models designed for , such as those with Cool Flow valves, enhance wearer comfort during prolonged use without compromising seal integrity. For rosin-based flux, which releases volatile organic compounds (VOCs), extraction units incorporating filters adsorb gaseous emissions, complementing high-efficiency particulate air () filtration for solids; combined systems maintain post-mitigation air concentrations below threshold limit values (TLVs) for colophony and metals. Operational practices further causal reductions in exposure include minimizing temperatures to the lowest effective level, thereby limiting decomposition and vaporization rates, though lead-free alloys necessitate higher settings (typically 30-50°C above leaded counterparts) that can elevate fume output if not offset by robust ventilation. Transitioning to lead-free solders reduces heavy metal risks where process reliability permits, as these alloys produce fewer toxic particulates despite increased thermal demands; however, empirical data indicate potential trade-offs in joint integrity under thermal cycling, underscoring the need for alloy-specific validation. Routine filter maintenance and airflow monitoring ensure sustained efficacy, with integrated sensors verifying capture below PELs like OSHA's 50 μg/m³ for lead.

Regulations and Controversies

Global Standards and Lead Restrictions

The European Union's Restriction of Hazardous Substances (RoHS) Directive (2002/95/EC), enforced from July 1, 2006, limits lead concentration to a maximum of 0.1% by weight in homogeneous materials, including solders, within electrical and electronic placed on the market. This threshold applies to categories such as tin-lead alloys traditionally used in assembly, compelling manufacturers to reformulate solders to comply for exports and sales. The Directive's scope expanded under RoHS 2 (2011/65/EU) to cover additional product categories, with periodic reviews of exemptions for high-lead solders exceeding 85% lead by weight in specialized applications. Complementing RoHS, the Waste Electrical and Electronic Equipment (WEEE) Directive (2002/96/EC, recast as 2012/19/EU) imposes obligations on producers for the collection, treatment, and of , targeting recovery rates such as 85% by weight for large household appliances and promoting separate collection to reduce disposal of lead-containing materials. These regulations drove empirical shifts in global supply chains, with widespread adoption of tin-silver-copper (SAC) alloys like SAC305 (96.5% Sn, 3% Ag, 0.5% Cu) as primary lead-free alternatives by around 2010, following qualification under industry standards. In the United States, lacking a federal RoHS equivalent, lead-based solders remain available for domestic use, with exemptions preserved in defense and medical sectors through Department of Defense procurement policies prioritizing reliability over environmental mandates. Organizations like established qualification standards, including JESD22-B102 for testing and J-STD-020 for moisture/reflow sensitivity, to validate lead-free processes against thermal and mechanical stresses. Compliance has entailed causal adjustments, such as elevating reflow peak temperatures to 260°C for SAC alloys versus 225°C for tin-lead, thereby raising demands through prolonged oven dwell times and higher thermal profiles. The regulatory push correlates with solder market expansion, valued at approximately $2.15 billion for alloys in and projected to grow amid demand, though exact figures vary by segment.

Debates on Lead-Free Mandates and Performance Trade-offs

Lead-free solder mandates, primarily enacted through the European Union's RoHS Directive in , aimed to minimize environmental lead contamination from by restricting lead content in solders to below 0.1%. Proponents argue this reduces leaching risks in landfills, with studies estimating that lead from solders constitutes a minor but cumulative hazard in e-waste, potentially contaminating and water if not properly. However, empirical analyses question the magnitude of these benefits, noting that solder lead represents less than 1% of total electronic lead content—dominated instead by batteries and CRTs—and that advanced processes already mitigate leaching effectively, rendering the environmental gains marginal relative to compliance costs. Critics of universal mandates highlight performance trade-offs, particularly in reliability-critical applications, where tin-lead (SnPb) solders exhibit superior and resistance compared to lead-free alternatives like SAC305 (Sn-Ag-Cu). For instance, SnPb joints demonstrate lower crack propagation rates under thermal cycling, with testing revealing up to 20-50% extended characteristic life in some high-stress scenarios versus SAC, due to the latter's higher stiffness and brittleness. Transitioning also demands higher reflow temperatures (around 260°C for SAC versus 183°C for eutectic SnPb), escalating rework energy use by 30-50% and risking damage to heat-sensitive components like plastics or adhesives. A key contention involves tin whisker growth, a spontaneous phenomenon in high-tin lead-free solders that forms conductive filaments capable of short-circuiting components; lead in SnPb alloys suppresses this by over 90%. has documented whisker-induced failures and hardware, attributing them causally to lead-free mandates and advocating exemptions, as mitigation strategies like conformal coatings add complexity without full reliability assurance. Industry reports from echo these concerns, contrasting regulatory absolutism—often influenced by precautionary environmental policies—with data-driven needs for selection tailored to and environment, as blanket restrictions overlook SnPb's proven track record in vibration and long-term thermal exposure. These debates underscore policy tensions, with exemptions granted to sectors like defense and validating context-specific approaches over one-size-fits-all rules; for example, the U.S. DoD and ESA permit SnPb use where failure risks outweigh environmental increments. While lead-free adoption has spurred innovations, empirical failure analyses indicate elevated crack initiation in SAC under combined stresses, prompting calls for risk-based regulations rather than mandates that prioritize unquantified ecological ideals over verifiable outcomes.

Recent Developments

Alloy Innovations and Reliability Improvements

Recent advancements in Sn-Ag-Cu (SAC) solder alloys have incorporated dopants such as (Bi) and (Ni) to suppress tin whisker growth, a persistent reliability issue arising from compressive stresses in pure tin phases. Bi additions form evenly distributed softer grains within the tin lattice, locally relieving mechanical stress and promoting short Bi whiskers over hazardous long tin ones, as demonstrated in microstructural analyses of modified SAC compositions. Ni doping similarly enhances whisker resistance in low-Ag SAC variants by refining compounds and improving barriers, with empirical tests showing reduced whisker propensity under accelerated environmental conditions. These post-2020 formulations address causal mechanisms of whisker initiation, including and oxidation, without compromising joint integrity. Low-silver SAC alloys, often below 1-3 wt.% Ag, have gained traction for amid silver price volatility, while dopants like (Mn) or (Ce) sustain or enhance reliability metrics such as drop shock resistance and thermal cycling endurance. For instance, SAC-Mn and SAC-Ce exhibit lower degradation rates post-aging compared to undoped high-Ag SAC305, with retention improved by 20-30% in dynamic bending tests due to stabilized microstructures. These alloys mitigate in layers, a common failure mode in low-Ag systems, through controlled that refines and disperses stresses. The global tin solder market, heavily reliant on such SAC innovations, reached USD 5.215 billion in 2024, with projections indicating sustained growth driven by demand for economical, high-reliability assembly. Ultrafine solder pastes utilizing Type 6 (15-20 μm) or smaller powders have emerged for precision applications in AI , enabling void-free joints in sub-150 μm apertures critical for integration. These pastes reduce warpage in heterogeneous assemblies by promoting uniform reflow and minimizing coefficient of mismatches, as evidenced by finite element modeling and empirical print transfer efficiency data exceeding 90% for fine-pitch stencils. Trends from the 2025 IEEE Electronic Components and Technology Conference underscore their role in mitigating thermomechanical stresses in advanced node s, where finer particle distributions lower peak temperatures and enhance standoff control during reflow. Interlayer materials, such as diffusion barriers or compliant underlayers in Sn-based joints, extend fatigue life by modulating compound growth rates, verifiable through accelerated isothermal aging and thermal cycling protocols. Studies post-2020 reveal that optimized interlayers slow Cu3Sn phase thickening— a primary degradation vector—resulting in 15-50% longer cycles to in highly accelerated test conditions simulating 10-20 years of service. This causal enhancement stems from reduced atomic across interfaces, preserving solder bulk properties against voiding and cracking, with shear strength post-aging retaining over 70% of initial values in doped Sn systems.

Automation and Process Advancements

Recent advancements in automation have integrated -based robotic systems, which offer precise, non-contact heating for delicate components. The global automatic robot market was valued at USD 84 million in 2024 and is projected to reach USD 118 million by 2032, growing at a (CAGR) of 5.1%, driven by demand in for high-speed, consistent joint formation. These systems reduce on substrates compared to traditional methods, enabling applications in advanced packaging where tolerances are sub-millimeter. Artificial intelligence (AI) has been incorporated into soldering stations for predictive maintenance and process optimization, with notable releases showcased at events like Productronica 2023. AI-enabled diagnostics in dual-channel digital soldering stations monitor parameters such as fluctuations and solder flow in real-time, forecasting potential failures to minimize downtime. Market analyses indicate that such integrations support Industry 4.0 transitions by enhancing yield rates through adaptive algorithms that adjust soldering parameters based on historical data. Selective soldering processes have seen expanded adoption for through-hole components on mixed-technology boards, with the market valued at USD 194.7 million in 2024 and expected to grow at a 5.1% CAGR through the forecast period. This technique uses targeted nozzles for application and solder wave exposure, improving precision in high-density assemblies and reducing masking requirements, which causally lowers rework by avoiding blanket reflow exposure. Integration of (IoT) sensors in soldering lines facilitates real-time monitoring of variables like humidity, vibration, and joint integrity, contributing to defect reductions in Industry 4.0 environments. In electronics manufacturing, IoT-driven has been reported to decrease soldering defects by ensuring consistent adherence, with broader manufacturing studies showing up to 30% reductions in unplanned issues through . These advancements collectively project a forward trajectory toward fully autonomous lines, where refines causal links between process inputs and joint reliability, potentially elevating throughput by 20-50% in high-volume production by 2030.

References

  1. https://resources.pcb.cadence.com/blog/what-are-the-different-types-of-solder-2
  2. https://www.tescaglobal.com/blog/what-is-soldering/
  3. https://www.ametekaegis.com/resources/design-guideline/braze-solder
  4. https://www.indium.com/blog/soldering-101-ii-the-miracle-of-soldering/
  5. https://ts.kurtzersa.com/electronics-production-equipment/about-us/ersa-history/history-of-soldering.html
  6. https://www.oatey.com/faqs-blog-videos-case-studies/blog/what-are-the-different-types-of-solder
  7. https://www.wevolver.com/article/comparing-the-contrasts-lead-based-vs-lead-free-solder
  8. https://www.indium.com/blog/rohs-ten-years-later-the-transition-to-lead-free-electronics-assembly/
  9. https://pmc.ncbi.nlm.nih.gov/articles/PMC6735330/
  10. https://www.desolutions.com/blog/wp-content/uploads/2013/02/Lead-Free-Solder-Reliability-Issues-Test-Methods.pdf
  11. https://www.protoexpress.com/blog/ipc-j-std-001-standard-soldering-requirements/
  12. https://www.asminternational.org/results/-/journal_content/56/ASMHBA0001346/BOOK-ARTICLE/
  13. https://www.3dcircuitry.org/post/the-evolution-of-soldering-tracing-the-roots-of-this-timeless-craft
  14. https://www.intecag.ch/en/soldering-knowledge-_content---1--1007--13.html
  15. https://everything-everywhere.com/the-wonderful-world-of-tin/
  16. https://www.acdi.com/the-evolution-of-soldering-in-electronics-manufacturing/
  17. https://www.eejournal.com/article/a-brief-history-of-pcbs-where-did-printed-circuit-boards-come-from/
  18. https://www.ametek-coining.com/pressreleases/blog/2022/june/the-history-of-soldering
  19. https://emsginc.com/resources/the-evolution-of-surface-mount-technology/
  20. https://www.merriam-webster.com/dictionary/solder
  21. https://www.etymonline.com/word/solder
  22. https://www.oxfordlearnersdictionaries.com/us/definition/english/solder_2
  23. https://dl.asminternational.org/technical-books/monograph/174/chapter/3592847/History
  24. https://copper.org/applications/plumbing/techcorner/soldering_brazing_explained.php
  25. https://blog.sra-solder.com/knowledge-base/the-difference-between-soldering-brazing-and-welding
  26. https://esab.com/us/nam_en/esab-university/articles/difference-between-welding-brazing-and-soldering/
  27. https://cupalloys.co.uk/blog/understanding-capillary-action-in-silver-soldering/
  28. https://www.uti.edu/blog/welding/brazing-soldering-welding
  29. https://www.msed.nist.gov/solder/NIST_LeadfreeSolder_v4.pdf
  30. https://www.nextpcb.com/blog/lead-vs-lead-free-solder
  31. https://pmc.ncbi.nlm.nih.gov/articles/PMC11122834/
  32. https://www.jstage.jst.go.jp/article/jiepeng/2/1/2_1_29/_pdf
  33. https://arraysolders.com/wp-content/uploads/2023/06/TDS-63sn37pb.pdf
  34. https://www.metallurgy.nist.gov/solder/clech/Sn-Ag-Cu_Other.htm
  35. https://www.makeitfrom.com/material-properties/ISO-Solder-Alloy-101-Sn63Pb37
  36. https://en.szfitech.com/newsinfo129.html
  37. https://www.sciencedirect.com/science/article/abs/pii/S1359646298004175
  38. https://invacu.com/solder-alloys
  39. https://termopasty.com/en/soft-and-hard-soldering-key-differences-and-applications/
  40. https://fractory.com/soldering-explained/
  41. https://www.chengshengindustry.com/news/what-is-brazing-between-soft-brazing-hard-brazing.html
  42. https://www.wevolver.com/article/types-of-solder
  43. https://electronics.stackexchange.com/questions/281014/what-is-the-best-type-of-solder-for-strength-and-creep-resistance
  44. https://www.copper.org/applications/marine/cuni/pdf/Broschuere_Loeten_ENG.pdf
  45. https://www.ametek-coining.com/pressreleases/blog/2020/september/what-is-solder-melting-point
  46. https://www.aimsolder.com/products/sn63-pb37-leaded-solder-alloy/
  47. https://fctsolder.com/eutectic-solder/
  48. https://nmd-metalpowders.de/en/sn63pb37-t3-loetpulver/
  49. https://electronics.stackexchange.com/questions/330309/best-solder-wire-sn63pb37-vs-sn60pb40-vs-others
  50. https://www.raypcb.com/60_40-vs-63_37-solder/
  51. https://www.nextpcb.com/blog/60-40-vs-63-37-solder-what-are-their-similarities-and-differences
  52. https://www.semanticscholar.org/paper/Microstructure-evolution-of-tin-lead-solder-Ubachs-Schreurs/e2fec3c582ca040a594b628a8502482e578db952
  53. https://www.sciencedirect.com/science/article/pii/S2772370425000100
  54. https://www.mgchemicals.com/downloads/tds/tds-4925.pdf
  55. https://www.kester.com/downloads?Command=Core_Download&EntryId=45147
  56. https://www.sciencedirect.com/science/article/abs/pii/S0026271417302044
  57. https://www.caplinq.com/sac105-low-cost-sac-solder-spheres-with-excellent-fatigue-resistance-sac105.html
  58. https://www.circuitinsight.com/pdf/low_cost_sac_alloy_smta.pdf
  59. https://www.caplinq.com/bi58sn42-low-eutectic-temperature-lead-free-solder-spheres-bi58sn42.html
  60. https://circuitinsight.com/pdf/effects_phosphorus_lead_free_solders_smta.pdf
  61. https://www.researchgate.net/publication/248181727_Effect_of_phosphorus_element_on_the_comprehensive_properties_of_Sn-Cu_lead-free_solder
  62. https://www.azom.com/article.aspx?ArticleID=2377
  63. https://www.indium.com/es/blog/gold-tin-solder-alloy-applications-alloy-composition-choices/
  64. https://www.sciencedirect.com/science/article/pii/S259004982030062X
  65. https://www.sciencedirect.com/science/article/abs/pii/S1369800124009521
  66. https://www.circuitinsight.com/pdf/comprehensive_report_low_temperature_solder_smta.pdf
  67. https://www.sciencedirect.com/science/article/pii/S2238785425006635
  68. https://www.electronics.org/TOC/IPC-J-STD-006C.pdf
  69. https://link.springer.com/article/10.1007/s11664-020-08602-z
  70. https://www.chemtronics.com/essential-guide-to-flux-for-soldering-electronics
  71. https://mgchemicals.com/knowledgebase/guides/ultimate-guide-to-flux-removers/
  72. https://www.protoexpress.com/blog/soldering-flux-acids-solids-and-solvents/
  73. https://www.circuitnet.com/experts/43341.html
  74. https://www.researchgate.net/publication/394782834_Investigation_of_the_Solder_Fluxes_Activity_by_Measuring_of_the_Contact_Angle
  75. https://www.indium.com/blog/what-a-j-std-004-classification-of-or-means-and-what-it-doesnt-mean/
  76. https://www.electronics.org/TOC/J-STD-004BwAm1.pdf
  77. https://www.indium.com/blog/surface-preparation-for-flux-less-reflow-the-solution/
  78. https://blog.lucasmilhaupt.com/en-us/about/blog/brazing-surface-preparation
  79. https://www.harrisproductsgroup.com/en/Resources/Knowledge-Center/Articles/Procedures-for-Soldering
  80. https://www.circuitrework.com/guides/7-1-1.html
  81. https://tovatech.com/blog/609/ultrasonic-cleaner-blogs/ultrasonic-pcb-cleaner-for-safe-cleaning
  82. https://www.sciencedirect.com/science/article/abs/pii/S0257897201011811
  83. https://ieeexplore.ieee.org/iel8/11120875/11120894/11121025.pdf
  84. https://www.magazines007.com/pdf/SMT007-June2021.pdf
  85. https://www.electronics.org/blog/failure-analysis-case-studies-solder-de-wetting-electronics-products
  86. https://www.intechopen.com/chapters/70995
  87. https://www.pcbyes.com/index.php?route=information/news&news_id=58
  88. https://www.atetool.com/news/Mastering-Soldering-Iron-Temp:-The-Ultimate-Guide-for-Perfect-Joints.html
  89. https://www.techspray.com/ultimate-guide-to-electronic-soldering
  90. https://www.circuitnet.com/experts/88720.html
  91. https://www.7pcb.com/blog/why-ipc-a-610-requires-solder-joint
  92. https://electronics.stackexchange.com/questions/278090/manual-soldering-issues-and-advices
  93. https://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf
  94. https://www.oatey.com/how-solder-copper-pipes
  95. https://www.bernzomatic.com/Projects/Fix/Solder-Copper-Pipe
  96. https://www.soselectronic.com/en-us/articles/weller/practical-advice-for-quality-and-efficient-hand-soldering-2297
  97. https://electronicsgroup.co.uk/common-soldering-mistakes/
  98. https://info.zentech.com/blog/the-five-stages-of-smt-reflow-ovens
  99. https://www.btu.com/reflow-ovens/what-is-a-reflow-oven/
  100. https://www.protoexpress.com/blog/making-sense-wave-soldering/
  101. https://arshon.com/blog/wave-soldering-a-key-pcb-assembly-technique/
  102. https://www.allpcb.com/blog/pcb-manufacturing/navigating-the-waters-of-wave-soldering-for-through-hole-components-in-mass-production.html
  103. https://www.futuremarketinsights.com/reports/selective-soldering-market
  104. https://www.rp-photonics.com/laser_soldering.html
  105. https://kurtzersa.com/services/solder-wiki/laser-soldering
  106. https://www.manufacturingtomorrow.com/content.php?post=25990
  107. https://kohyoungamerica.com/ai-powered-aoi-the-key-to-higher-yields-and-smarter-factories/
  108. https://www.pneumatech.com/en-us/blog/the-benefits-of-reflow-soldering-with-nitrogen
  109. https://mpe.researchmfg.com/n2-reflow/
  110. https://ijsrm.net/index.php/ijsrm/article/download/6168/3839/18123
  111. https://www.researchgate.net/publication/387139502_Advanced_AI_Technologies_for_Defect_Prevention_and_Yield_Optimization_in_PCB_Manufacturing
  112. https://link.springer.com/content/pdf/10.1007/s11664-010-1353-7.pdf
  113. https://www.sciencedirect.com/science/article/abs/pii/S0921510798002025
  114. https://link.springer.com/content/pdf/10.1007/s11664-020-08433-y.pdf
  115. https://ieeexplore.ieee.org/document/1318265/
  116. https://www.sciencedirect.com/science/article/abs/pii/S0925838816307770
  117. https://www.sciencedirect.com/science/article/abs/pii/S0927025622001331
  118. https://pmc.ncbi.nlm.nih.gov/articles/PMC8875696/
  119. https://neurochrome.com/pages/choosing-solder
  120. https://stellartechnical.com/blogs/electronic-assembly-technical-resources/what-is-the-right-solder-wire-diameter-for-the-job
  121. https://www.pcbasic.com/blog/electrical_solder.html
  122. https://www.jarnistech.com/pcb-soldering
  123. http://www.jabil.com/blog/miniaturization-key-to-fabricating-the-future.html
  124. https://nepp.nasa.gov/workshops/etw2023/talks/13-JUN-TUE/1405_Ghaffarian_BGA_CL23-2931.pdf
  125. https://www.infineon.com/assets/row/public/documents/packages/infineon-board-assembly-recommendations-bga-package-v04-00-en.pdf
  126. https://www.caplinq.com/solder-spheres.html
  127. https://www.ansys.com/blog/thermal-cycling-failure-in-electronics
  128. https://www.sciencedirect.com/science/article/pii/S2214914724001272
  129. https://pmc.ncbi.nlm.nih.gov/articles/PMC11123225/
  130. https://ntrs.nasa.gov/api/citations/20000060832/downloads/20000060832.pdf
  131. https://www.harrisproductsgroup.com/en/Products/hpg-na-955
  132. https://www.sheret.com/account/catalog/product/1042166
  133. https://www.oatey.com/faqs-blog-videos-case-studies/blog/copper-pipes-plumbing-systems
  134. https://www.canfieldmetals.com/95_5_wire_solder.htm
  135. https://www.littlepeng.com/single-post/2017/09/25/asme-b313-limitations-on-miscellaneous-joints
  136. https://www.copper.org/environment/water/e_p_lead.html
  137. https://www.mcmaster.com/products/solder/food-industry-standard~nsf-ansi-61/
  138. https://www.crystalrugged.com/mil-std-810-test-method-514-6-vibration/
  139. https://eprintspublications.npl.co.uk/3979/1/MAT2.pdf
  140. https://ntrs.nasa.gov/api/citations/20100029736/downloads/20100029736.pdf
  141. https://www.navair.navy.mil/node/8221
  142. https://www.indium.com/blog/gold-based-solder-wire-for-high-reliability-applications/
  143. https://aerospace.org/node/3246/printable/print
  144. https://www.ansys.com/blog/solder-fatigue-causes-prevention
  145. https://www.sciencedirect.com/science/article/pii/S2351978917304444
  146. https://www.circuitinsight.com/pdf/controlling_voiding_mechanisms_reflow_soldering_process_ipc.pdf
  147. https://www.sciencedirect.com/science/article/abs/pii/S0026271403001240
  148. https://ieeexplore.ieee.org/document/5699647/
  149. https://www.sciencedirect.com/science/article/pii/S0264127520302604
  150. https://nepp.nasa.gov/whisker/background/
  151. https://pmc.ncbi.nlm.nih.gov/articles/PMC9925449/
  152. https://www.tandfonline.com/doi/full/10.1080/10589759.2022.2084616
  153. https://www.circuitinsight.com/pdf/second_generation_lead_free_alloys_smta.pdf
  154. https://www.researchgate.net/figure/Comparison-on-Youngs-modulus-obtained-by-different-researchers-and-our-model-the_fig3_245350976
  155. https://www.linkedin.com/pulse/comparison-reliability-leaded-lead-free-solder-joints-zvnpc
  156. https://journal.smta.org/index.php/smt/article/download/41/25/403
  157. https://www.sanmina.com/pdf/solutions/pcbres/impact_of_intermetallic_growth_on_leadfree_joints.pdf
  158. https://nepp.nasa.gov/whisker/reference/tech_papers/2006-Leidecker-Tin-Whisker-Failures.pdf
  159. https://www.indium.com/blog/tin-whiskers-found-in-nasa-study-of-toyota-unintended-acceleration-issue/
  160. https://www.lamar.edu/engineering/_files/documents/mechanical/dr.-fan-publications/2007/Fan%25202007_02%2520ECTC_1.pdf
  161. https://www.electronics.org/system/files/technical_resource/E18%2526S28-2.pdf
  162. https://pmc.ncbi.nlm.nih.gov/articles/PMC4961898/
  163. https://www.cdc.gov/lead-prevention/php/news-features/updates-blood-lead-reference-value.html
  164. https://pubmed.ncbi.nlm.nih.gov/30836127/
  165. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1025
  166. https://ehs.mit.edu/wp-content/uploads/EHS-0167.pdf
  167. https://www2.mst.dk/udgiv/publications/2003/87-7972-512-0/html/kap10_eng.htm
  168. https://img0.fastenal.com/productimages/supplemental/product_docs/LENOX_773814.pdf
  169. https://pmc.ncbi.nlm.nih.gov/articles/PMC3348243/
  170. https://www.occupationalasthma.com/occupational_asthma_causative_agent.aspx?id=82
  171. https://drs.illinois.edu/Page/SafetyLibrary/SolderingSafety
  172. https://fumedog.com/blogs/news/do-solder-fume-extractors-work
  173. https://www.sentryair.com/blog/industry-applications/electronics-technology/the-hazards-of-solder-fumes/
  174. https://www.3m.com/3M/en_US/p/d/v000057485/
  175. https://www.riogrande.com/product/3m-particulate-soldering-respirator-8515-n95/201683GP/
  176. https://www.sentryair.com/blog/industry-applications/soldering/comparing-solder-fume-extractors-its-all-about-the-filter/
  177. https://www.osha.gov/lead/evaluating-controlling-exposure
  178. https://www.sentryair.com/blog/product-review/fume-extractors/inorganic-lead-standard/
  179. https://www.electronics.org/system/files/technical_resource/E16%2526S09-02.pdf
  180. https://blog.matric.com/lead-vs-lead-free-solder-in-pcb-manufacturing
  181. https://rohs.exemptions.oeko.info/fileadmin/user_upload/Stakeholder_comments/Exemption-7a_5_Pecht_Uni_Maryland_25_March_2008.pdf
  182. https://environment.ec.europa.eu/topics/waste-and-recycling/waste-electrical-and-electronic-equipment-weee_en
  183. https://www.intechopen.com/chapters/55827
  184. https://www.militaryaerospace.com/home/article/16709446/lead-free-rohs-on-military-electronics-procurement
  185. https://www.jedec.org/sites/default/files/docs/22b102e.pdf
  186. https://ieeexplore.ieee.org/document/1040821/
  187. https://www.linkedin.com/pulse/solder-alloy-market-2026-ai-size-forecast-key-insights-9puhe
  188. https://www.electronicdesign.com/markets/energy/article/21772695/is-leadfree-solder-the-answer-to-our-environmental-problems
  189. https://www.sciencedirect.com/science/article/abs/pii/S0301479707001818
  190. https://19january2017snapshot.epa.gov/sites/production/files/2015-04/documents/solder_appendices.pdf
  191. https://nepp.nasa.gov/files/10981/NASA%2520Lead-Free%2520Solder%2520BOK%2520Appendices%2520May%25202005%2520%282%29.pdf
  192. https://imapsjmep.org/article/40285.pdf
  193. https://nepp.nasa.gov/whisker/reference/tech_papers/2007-barr-paper-mitigating-whiskers.pdf
  194. https://ieeexplore.ieee.org/iel8/6287639/10820123/11075682.pdf
  195. https://www.intelmarketresearch.com/automatic-laser-soldering-robot-2025-2032-915-4525
  196. https://kaisertech.co.uk/content/unveiling-the-future-of-electronics-a-recap-of-productronica-2023
  197. https://www.futuremarketreport.com/industry-report/dual-channel-digital-soldering-station-market/
  198. https://www.linkedin.com/pulse/soldering-irons-stations-market-comprehensive-analysis-ypsxc/
  199. https://www.reportsandinsights.com/report/selective-soldering-system-market
  200. https://www.databridgemarketresearch.com/reports/global-selective-soldering-market
  201. https://sumitron.com/future-of-electronics-manufacturing/
  202. https://multishoring.com/blog/iot-in-manufacturing-how-smart-sensors-can-cut-downtime/
  203. https://www.archivemarketresearch.com/reports/fully-automated-soldering-robot-207216
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