More on CD & CDR Manufacturing...

Most CDs that are manufactured in a CD plant are done so by a process, which starts by using a laser beam recorder to expose a spiral track on the surface of a glass, substrate disc coated with a light sensitive photo resist material. This "Glass Master" is then chemically developed, causing the area exposed by the laser to be washed away, forming pits on the surface of the disc. It is these pits that the laser on a CD player reads to interpret the data on the disc once it is finally made into a compact disk. Next, under a very high vacuum a thin layer of nickel is sputtered onto the photo resist surface of the glass disc, making the surface conductive to electricity. The nickel coating is built up to the required thickness of a stamper by electroplating. This stamper is peeled from the surface of the glass, cleaned then back polished and punched to form a stamper 0.285mm thick. The stamper is then loaded into an injection moulder where molten polycarbonate is injected under high pressure. A clear disc is formed with the data track molded by the stamper on one side. The data side is now coated under a vacuum with a reflective layer of aluminum. The aluminum layer is then sealed and protected by a liquid polymer resin spun on and quickly cured by U.V. light. The disc can now be screen printed on the protective layer to finish the Compact Disk.

With a recordable CD, or CDR there is a layer of organic dye between the polycarbonate substrate and reflective aluminum layer. When heated with the laser from a CD burner, the dye melts and forms areas that act like the pits on a stamped CD. A spiral pre-groove in polycarbonate substrate helps guide the laser and performs other control and timing operations while recording.

There a many variables when it comes to making recordable CD's that can make the difference between a CDR that will work on some players or CD ROM but not on others. This is normally related to the amount of unrecoverable errors that are present when reading the disk. The disc alone does not only determine the amount of errors but how the total system, CD player included performs. Interestingly, all CDs and CDR's produce thousands of errors while playing back as CD players are operating at the limits of physical law. All CDs incorporate Cross Interleave Reed-Solomon Code (CIRC), a powerful error correction code that can detect and correct all the errors on a reasonably good disk.

A number of factors can determine the amount and type of errors present on the disk itself. From the type of media you maybe using, the software and the way your computer and burner is configured, or even just dust or vibration during the burning can affect the integrity of the data on the CDR. This may not be a concern when you are making disks for your own use, but in replicating larger numbers for use in many situations it can be wise to make sure your CD's are professionally replicated.