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The process of Replicating CDs and DVDs involves several stages, and can also be done using different, although similar, techniques. There are also some differences between the Replication process of CDs and DVDs, with DVDs requiring smaller pits than CDs, but again the processes are quite similar.
The initial stage of the Replication process is the pre-mastering stage. This reiterates the preparation of the data / information that is to go onto the CD or DVD to create a data source. In all cases, this needs to be in digital format, however the data source can be on a CD-R or on the hard drive of a computer. Another, less common data source used are digital master tapes, but these can only be used for duplicating audio CDs. In all cases, except where CD-R data sources are used, a table of contents (TOC) must be created so that any device that reads the final CD can find the data contained on it.
The mastering process then takes two stages. Firstly, there is the glass mastering stage, followed by either photoresist mastering or non-photoresist / dye-polymer mastering to create the peaks and pits on the disk before going onto the post-mastering stage.
During the glass mastering stage, glass is used to hold the master image that is to go onto the CD while the replication takes place. This is known as the 'master disc'. A glass plate, larger than the size of a CD, are created with one side polished very smooth to remove and fine scratches or other imperfections that could affect the quality of the final CD or DVD. The glass disc is then cleaned with detergents and ultrasonic baths and placed in a spin coater, where the disc is then blackened with a solvent. The spin coater then applies either a photoresist or dye-polymer coating before the glass disc is removed and dried ready to be used to duplicate the CDs or DVDs.
Once the glass disk is ready, a laser is used to write the data onto it for both photoresist mastering and dye-polymer mastering. Photoresist mastering is done using materials that are sensitive to light to create the pits and lands on the master disk. These light sensitive materials are exposed to a blue or ultraviolet laser, causing the materials to react chemically and harden. The master disk is then soaked in a developer fluid that removes either the hardened or unharmed parts of the disc, leaving the required data print. The disc is the developed, metalised and polished.
Non-photoresist, or dye-polymer, mastering directly creates the pits onto the surface of the glass master disc. Where the laser is focused on the disc, the dye polymer absorbs the energy and then vaporises, forming a pit on the surface of the dye-polymer coating. This gives the advantage of being able to read the master disc as it is being created, usually by an attached 'red read laser', and make any adjustments to errors in the recording due to imperfections in the dye-polymer coating or other causes.
The next stage of creating the master disc for the replication of CDs and DVDs is post mastering. During post mastering, the glass master disc is baked so that it hardens the surface and is then electroplated with nickel, before the disc is inspected for any imperfections.
The final step in preparing the master disc is electroforming. This toughens the disc so it can be used in the equipment to produce the end product CDs and DVDs, as the glass disc would otherwise be too easy to damage and the quality of the recording can easily become compromised.
Once the master disc has been created, polycarbonate injection molding machines that operate at high temperatures are then used to replicate the master disc for the desired quantity of copies.
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