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-Audio) or data form (CD-ROM). This process is used in the mastering of read-only compact discs; CD-Rs, CD-RWs, and DVDs are made somewhat differently, though the methods are broadly similar.

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 or better clean room; they can usually be manufactured to quite strict manufacturing tolerances for only a few US cents per disk.

CD mastering differs from burning, as the pits and lands of a mastered 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 'writes' the entire disk in one physical stamping operation.

Premastering :- 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 or Umatic formats. 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 the 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.

Post-mastering :- After mastering, the glass master is baked to harden the developed surface material to prepare it for metalisation. Metalisation is a critical step prior to electrogalvanic manufacture (electroplating).

The developed glass master is placed in a vapour deposition metaliser which uses a combination of mechanical vacuum pumps and cryopumps to lower the total vapour pressure inside a chamber to a hard vacuum. A piece of nickel wire is then heated in a tungsten boat to white hot temperature and the nickel vapour deposited onto the rotating glass master. The glass master is coated with the nickel vapour up to a typical thickness of around 400nm.

The finished glass masters are inspected for stains, pinholes or incomplete coverage of the nickel coating and passed to the next step in the mastering process.