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Tin-silver-copper
Tin-silver-copper (Sn-Ag-Cu, also known as SAC), is a lead-free (Pb-free) alloy commonly used for electronic solder. It is the main choice for lead-free surface-mount technology (SMT) assembly in the industry, as it is near eutectic, with adequate thermal fatigue properties, strength, and wettability. Lead-free solder has gained attention as the environmental effects of lead in industrial products have been recognized, and as a result of Europe's RoHS legislation to remove lead and other hazardous materials from electronics. Japanese electronics companies have also looked at Pb-free solder for its industrial advantages.
Typical alloys are 3–4% silver, 0.5–0.7% copper, and the balance (95%+) tin. For example, the common "SAC305" solder is 3.0% silver and 0.5% copper. Cheaper alternatives with less silver are used in some applications, such as SAC105 and SAC0307 (0.3% silver, 0.7% copper), at the expense of a somewhat higher melting point.
In addition to traditional silver-containing SAC alloys, silver-free tin-copper based alloys with minor additions of nickel and germanium have been developed to enhance mechanical and reliability properties while reducing material costs. One such alloy, SN100CV (Sn-1.5Bi-0.7Cu-Ni-Ge), is designed as a drop-in replacement for SAC305 solder in surface-mount assembly processes. According to standardized IPC testing, SN100CV solder paste demonstrates excellent flux activity, wetting, and slump stability suitable for reflow soldering. It exhibits strong corrosion resistance evidenced by high surface insulation resistance and electrochemical migration resistance after prolonged environmental stress. These properties suggest improved long-term joint reliability and mechanical stability, making SN100CV a viable alternative to traditional SAC alloys in various electronic assembly applications.
Despite widespread regulatory encouragement, the transition to lead-free solders such as SAC alloys faced significant technical challenges. Misconceptions about melting points, solder joint reliability, and equipment compatibility initially complicated manufacturing adoption. Practical industry experience has shown that selecting eutectic or near-eutectic alloys and carefully adapting reflow processes and flux chemistry are critical to achieving reliable solder joints. Challenges including fillet lifting, corrosion potential, and changes in mechanical stress response required focused research and process optimization. Continued development and understanding of these phenomena have enabled SAC solders to achieve performance levels comparable to traditional tin-lead solders in many applications.
In 2000, there were several lead-free assemblies and chip products initiatives being driven by the Japan Electronic Industries Development Association (JEIDA) and Waste Electrical and Electronic Equipment Directive (WEEE). These initiatives resulted in tin-silver-copper alloys being considered and tested as lead-free solder ball alternatives for array product assemblies.
In 2003, tin-silver-copper was being used as a lead-free solder. However, its performance was criticized because it left a dull, irregular finish and it was difficult to keep the copper content under control. In 2005, tin-silver-copper alloys constituted approximately 65% of lead-free alloys used in the industry and this percentage has been increasing. Large companies such as Sony and Intel switched from using lead-containing solder to a tin-silver-copper alloy.
The process requirements for (Pb-free) SAC solders and Sn-Pb solders are different both materially and logistically for electronic assembly. In addition, the reliability of Sn-Pb solders is well established, while SAC solders are still undergoing study, (though much work has been done to justify the use of SAC solders, such as the iNEMI Lead Free Solder Project).
One important difference is that Pb-free soldering requires higher temperatures and increased process control to achieve the same results as that of the tin-lead method. The melting point of SAC alloys is 217–220 °C, or about 34 °C higher than the melting point of the eutectic tin-lead (63/37) alloy. This requires peak temperatures in the range of 235–245 °C to achieve wetting and wicking.
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Tin-silver-copper
Tin-silver-copper (Sn-Ag-Cu, also known as SAC), is a lead-free (Pb-free) alloy commonly used for electronic solder. It is the main choice for lead-free surface-mount technology (SMT) assembly in the industry, as it is near eutectic, with adequate thermal fatigue properties, strength, and wettability. Lead-free solder has gained attention as the environmental effects of lead in industrial products have been recognized, and as a result of Europe's RoHS legislation to remove lead and other hazardous materials from electronics. Japanese electronics companies have also looked at Pb-free solder for its industrial advantages.
Typical alloys are 3–4% silver, 0.5–0.7% copper, and the balance (95%+) tin. For example, the common "SAC305" solder is 3.0% silver and 0.5% copper. Cheaper alternatives with less silver are used in some applications, such as SAC105 and SAC0307 (0.3% silver, 0.7% copper), at the expense of a somewhat higher melting point.
In addition to traditional silver-containing SAC alloys, silver-free tin-copper based alloys with minor additions of nickel and germanium have been developed to enhance mechanical and reliability properties while reducing material costs. One such alloy, SN100CV (Sn-1.5Bi-0.7Cu-Ni-Ge), is designed as a drop-in replacement for SAC305 solder in surface-mount assembly processes. According to standardized IPC testing, SN100CV solder paste demonstrates excellent flux activity, wetting, and slump stability suitable for reflow soldering. It exhibits strong corrosion resistance evidenced by high surface insulation resistance and electrochemical migration resistance after prolonged environmental stress. These properties suggest improved long-term joint reliability and mechanical stability, making SN100CV a viable alternative to traditional SAC alloys in various electronic assembly applications.
Despite widespread regulatory encouragement, the transition to lead-free solders such as SAC alloys faced significant technical challenges. Misconceptions about melting points, solder joint reliability, and equipment compatibility initially complicated manufacturing adoption. Practical industry experience has shown that selecting eutectic or near-eutectic alloys and carefully adapting reflow processes and flux chemistry are critical to achieving reliable solder joints. Challenges including fillet lifting, corrosion potential, and changes in mechanical stress response required focused research and process optimization. Continued development and understanding of these phenomena have enabled SAC solders to achieve performance levels comparable to traditional tin-lead solders in many applications.
In 2000, there were several lead-free assemblies and chip products initiatives being driven by the Japan Electronic Industries Development Association (JEIDA) and Waste Electrical and Electronic Equipment Directive (WEEE). These initiatives resulted in tin-silver-copper alloys being considered and tested as lead-free solder ball alternatives for array product assemblies.
In 2003, tin-silver-copper was being used as a lead-free solder. However, its performance was criticized because it left a dull, irregular finish and it was difficult to keep the copper content under control. In 2005, tin-silver-copper alloys constituted approximately 65% of lead-free alloys used in the industry and this percentage has been increasing. Large companies such as Sony and Intel switched from using lead-containing solder to a tin-silver-copper alloy.
The process requirements for (Pb-free) SAC solders and Sn-Pb solders are different both materially and logistically for electronic assembly. In addition, the reliability of Sn-Pb solders is well established, while SAC solders are still undergoing study, (though much work has been done to justify the use of SAC solders, such as the iNEMI Lead Free Solder Project).
One important difference is that Pb-free soldering requires higher temperatures and increased process control to achieve the same results as that of the tin-lead method. The melting point of SAC alloys is 217–220 °C, or about 34 °C higher than the melting point of the eutectic tin-lead (63/37) alloy. This requires peak temperatures in the range of 235–245 °C to achieve wetting and wicking.