Glass mastering and pressing

Glass mastering is the most crucial and complicated part of CD and DVD Replication, requiring technology and skill. Glass mastering is performed free of charge for standard CD/DVD replication above 3000 units.

Once a customer sends us a final 'pre-mastered' disc (generally a CD-R or DVD-R Duplication master disc) we begin the glass mastering process.

Please note that our customers, including audio CD Mastering facilities (eq, compression, digital assembly services) do not send us glass masters. MJK DP will have the glass master made for you!

CD Glass Mastering comprises a number of stages needed to create a metallized glass master from which the stampers are produced. The processes are carried out in a Class 1000 clean room. Operators wear special clothing including face masks and footwear to minimize any particles.

All CD-ROMs require glass mastering. It is a critical step in making CDs. CD-R Replication does not use this process. CD-R uses a stand alone hardware burner which etches laser light into a light-sensitive chemical substrate.

Customer provides the "Input Media"

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Procedure

Glass Master preparation of the 20 cm (8 inch) diameter 6mm thick glass master starts by stripping the old photo-resist from its surface (since the glass blanks can be recycled). This is followed by cleaning and final washing using de-ionized water. The blank master is then dried carefully and ready for the next stage. The surface of the clean glass master is then coated with a photo-resist layer 150 microns thick by spin coating. The uniformity of the layer is measured with an infra red laser. The photo-resist coated glass master is then baked at about 80 degrees Celcius for 30 minutes. This hardens the photo-resist layer ready for exposing by laser light.

Laser Beam Recording is where the photo-resist layer is exposed with laser light in a Class 1000 clean room-controlled environment using a blue gas laser directly from the source audio or CD-ROM data.

The photo-resist is exposed where pits are to be pressed in the final disc. The photo-resist surface is then developed to remove the photo-resist exposed by the laser and therefore create pits in the surface. These pits should extend right through the photo-resist to the glass underneath to achieve good pit geometries as specified in the Red Book. The glass itself is unaffected by this process.

The active surface (called the "father" - containing pits) of the developed glass master is then metallized either with silver by evaporation or a nickel or nickel alloy created by sputtering. The glass master is then played on a Disc Master Player (DMP) to check for any errors. Audio masters are actually listened to at this stage.

The final stage is then making the reverse image stamper or "mother". The mother is then form-pressed onto the extruded "children" membranes using high speed hydraulic presses. This membrane will ultimately contain all the binary information used to play the disc.

The finished compact disc that the customer receives is a combination of the child's membrane layer, an aluminum layer which reflects the laser light back up into the player, and a polycarbonate (plastic extrusion) outer shell. The final disc must be perfectly uniform and well balanced if the disc is to perform flawlessly. CD-ROM data players can now spin at extremely fast speeds. If your disc is not manufactured under ISO9002 procedures then flaws (and headaches) may result.

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