Compact Disk Cleaning: Cleaning Glass Master Disks - Aqueous Chemistry and Solvent Drying

Ultrasonic cleaning technology brings substantial savings to the compact disc recording industry by enabling the reuse of six-millimeter thick glass master disc upon which the musical information is laser etched. Previously, these master discs were disposed after a single use because critical cleaning could not be achieved. Ultrasonic cleaning lowers the production cost of compact discs, an important factor to the future growth of the CD market. The heavy glass substrate, approximately a foot in diameter, receives an ultrathin layer of adhesive and a photoresist coating. It is then exposed to a laser beam which cuts microscopic pits into the photoresist, forming the code to be interpreted into music on a CD player. Because the pits are microscopic, even a single dust particle - large by comparison - can disrupt the recording, so cleaning is critical. The glass master then is immersed in a chemical solution that etches away areas exposed to the laser light and silver is thin deposited over the etched photoresist.