Compact disc manufacturing

Compact disc manufacturing is the process by which commercial compact discs (CDs) are replicated in mass quantities using a master version created from a source recording. This may be either in audio form (CD-DA) or data form (CD-ROM). This process is used in the mastering of read-only compact discs. DVDs and Blu-rays use similar methods (see Optical Disc § Optical disc manufacturing).

A CD can be used to store audio, video, and data in various standardized formats defined in the Rainbow Books. CDs are usually manufactured in a class 100 (ISO 5) or better clean room, to avoid contamination which would result in data corruption. They can be manufactured to strict manufacturing tolerances for only a few US cents per disk.

Replication differs from duplication (i.e. burning used for CD-Rs and CD-RWs) as the pits and lands of a replicated CD are moulded into a CD blank, rather than being burn marks in a dye layer (in CD-Rs) or areas with changed physical characteristics (in CD-RWs). In addition, CD burners write data sequentially, while a CD pressing plant forms the entire disk in one physical stamping operation, similar to record pressing.

All CDs are pressed from a digital data source, with the most common sources being low error-rate CD-Rs or files from an attached computer hard drive containing the finished data (e. g., music or computer data). Some CD pressing systems can use digital master tapes, either in Digital Audio Tape, Exabyte, Digital Linear Tape, Digital Audio Stationary Head or Umatic formats. A PCM adaptor is used to record and retrieve digital audio data into and from an analog videocassette format such as Umatic or Betamax. However, such sources are suitable only for production of audio CDs due to error detection and correction issues. If the source is not a CD, the table of contents for the CD to be pressed must also be prepared and stored on a tape or hard drive. In all cases except CD-R sources, the tape must be uploaded to a media mastering system to create the TOC (Table of Contents) for the CD. Creative processing of the mixed audio recordings often occurs in conventional CD premastering sessions. While "mastering" is commonly used by laypeople to describe this phase, official industry terminology refers to it as "premastering," as it precedes the creation of the glass master from which stamper plates are electroformed.

Glass mastering is performed in a class 100 (ISO 5) or better clean room or a self-enclosed clean environment within the mastering system. Contaminants introduced during critical stages of manufacturing (e.g., dust, pollen, hair, or smoke) can cause sufficient errors to make a master unusable. Once successfully completed, a CD master will be less susceptible to the effects of these contaminants.

During glass mastering, glass is used as a substrate to hold the CD master image while it is created and processed; hence the name. Glass substrates, noticeably larger than a CD, are round plates of glass approximately 240 mm in diameter and 6 mm thick. They often also have a small, steel hub on one side to facilitate handling. The substrates are created especially for CD mastering and one side is polished until it is extremely smooth. Even microscopic scratches in the glass will affect the quality of CDs pressed from the master image. The extra area on the substrate allows for easier handling of the glass master and reduces the risk of damage to the pit and land structure when the "father" stamper is removed from the glass substrate.

Once the glass substrate is cleaned using detergents and ultrasonic baths, the glass is placed in a spin coater. The spin coater rinses the glass blank with a solvent and then applies either photoresist or dye-polymer depending on the mastering process. Rotation spreads photoresist or dye-polymer coating evenly across the surface of the glass. The substrate is removed and baked to dry the coating and the glass substrate is ready for mastering.

Once the glass is ready for mastering, it is placed in a laser beam recorder (LBR). Most LBRs are capable of mastering at greater than 1x speed, but due to the weight of the glass substrate and the requirements of a CD master they are typically mastered at no greater than 8x playback speed. The LBR uses a laser to write the information, with a wavelength and final lens NA (numerical aperture) chosen to produce the required pit size on the master blank. For example, DVD pits are smaller than CD pits, so a shorter wavelength or higher NA (or both) is needed for DVD mastering. LBRs use one of two recording techniques; photoresist and non-photoresist mastering. Photoresist also comes in two variations; positive photoresist and negative photoresist.