Compact 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.

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).

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.

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.

Contaminants introduced during critical stages of manufacturing (e.g., dust, pollen, hair, or smoke) can cause sufficient errors to make a master unusable.

Even microscopic scratches in the glass will affect the quality of CDs pressed from the master image.

The spin coater rinses the glass blank with a solvent and then applies either photoresist or dye-polymer depending on the mastering process.

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.

Another advantage of this method is that pit depth variation can be programmed during recording to compensate for downstream characteristics of the local production process (e.g., marginal molding performance).

This type of mastering is called Direct Read After Write (DRAW) and is the main advantage of some non-photoresist recording systems.

Problems with the quality of the glass blank master, such as scratches, or an uneven dye-polymer coating, can be immediately detected.

on the metalised glass master is extremely easy to damage and must be transferred to a tougher form for use in the injection moulding equipment which actually produces the end-product optical disks.

The metalised master is clamped in a conductive electrodeposition frame with the data side facing outwards and lowered into an electroforming tank.

The solution is carefully buffered to maintain its pH, and organic contaminants must be kept below one part in five million for good results.

The father is washed with deionised water and other chemicals such as ammonical hydrogen peroxide, sodium hydroxide or acetone to remove all trace of resist or other contaminants.

This time the metal part that is grown is the mirror image of the father and is called a "mother"; as this is now pits, it cannot be used for moulding.

The mother-father sandwich is carefully separated and the mother is then washed, passivated and returned to the electroforming baths to have a mirror image produced on it called a son.

Clear polycarbonate pellets are first dried at around 130 degrees Celsius for three hours (nominal; this depends on which optical grade resin is in use) and are fed via vacuum transport into one end of the injection moulder's barrel (i.e., the feed throat) and are moved to the injection chamber via a large screw inside the barrel.

The barrel, wrapped with heater bands ranging in temperature from ca 210 to 320 degrees Celsius melts the polycarbonate.

The discs pass, one at a time, into the metallizer, a small chamber at approximately 10−3 Torr (130 mPa) vacuum.

There is a load-lock system (similar to an airlock) so the process chamber can be kept at high vacuum as the discs are exchanged.

After metalisation, the discs pass on to a spin-coater, where UV curable lacquer is dispensed onto the newly metallized layer.

By rapid spinning, the lacquer coats the entire disc with a very thin layer (approximately 5 to 10 μm[4]).

The metal stamper can also be tested on a signal analysis machine which has been specially adapted (larger diameter, more fragile, ...).