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Frequently Asked Questions About CD-R and CD-RW Discs |
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Frequently Asked Questions About CD-R and CD-RW Discs |
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Although technical characteristics of the CD-R writer and disc are important, along with premastering software, dust and debris on the surface of the disc can generate permanent defects in the dye layer during recording. Any foreign matter on the readout surface will partially mask the recording laser beam, resulting in a loss of light intensity and poor quality. Such contaminants degrade quality a second time when the disc is read.
CD-ROM discs are mastered and recorded under clean room conditions. Personnel wear protective clothing to minimize contamination, HEPA filtration removes particulates in the air, laminar flow avoids convective currents, positive pressure avoids migration of dirty air from areas that surround the clean room, and debris generation is avoided through the use of non-linting materials in the clean area. In contrast, CD-R recording is often conducted in a dusty office environment.
An actual clean room for CD-R writers is ideal, but a regularly cleaned room with a tiled floor is acceptable provided that access is limited. Avoid carpeted areas where traffic generates clouds of dust. Use a grounded, static dissipative bench mat to minimize dust buildup related to static charge. Limit the number of personnel in the recording area, and minimize traffic to control airborne dust and other contaminants.
CD-R discs are insulators and retain static charges that attract and hold dust, fibers, and other contaminants. Grounding discs will not help because they are insulators, and charges cannot readily flow to the ground contact point. Instead, use an ionizing blower to discharge CD-R discs at any workstation. Such blowers create an airflow containing both positive and negative ions. Any static charge on a disc held in this airflow will attract ions of the opposite charge until the disc is discharged to ground potential.
Ionizing blowers range from small fans for local use to large, overhead units that blanket an entire room. Popular manufacturers are 3M, Charleswarer, Ion Systems, and Simco. They are readily available from distributors of electronic assembly equipment:
One small, convenient blower is the Ion Systems ZStat 6430:
Be very careful when blowing off dust using pressurized cans of clean air. The propellant can locally chill the disc. Micro-cracks are then visible after the frost evaporates. System compressed air can contain water or debris, and usually is electrically charged. This charge will be transferred to the CD-R disc where it then captures more dust. Loose debris can be removed using a clean, lint-free dry wiper and gentle radial strokes. Never use circular strokes that can accidentally create a microscratch along the track. Use only minimal pressure, and first neutralize static charges as described above. Avoid abrasive agents or solvents that can damage the disc.
Verify that your discs are free of debris just before recording. Halogen inspection lamps with 3 or 4 diopter magnifiers are available from many sources including the following companies:
High quality writers, discs, and software cannot overcome the effects of contaminants on the readout surface of a CD-R that partially mask the laser beam. The shadows of surface contaminants writes permanent defects in the dye layer during recording, and will cause additional errors when the disc is read. Clean discs and a clean environment are essential to good CD-R quality.
