CD Technology

The first step in the CD production process is the premastering of the audio, video or computer data. After the programme has been edited it's mastered on CD-R or another digital medium. A glass plate for the glass master is polished, cleaned and provided with a photosensitive coating. Next the programme is transferred to the glass master through laser beam cutting, after which the glass master is developed and silver-plated. During the galvanic procedure, the silver layer on the glass master with the numeric information is used as cathode with a nickel anode and by means of electrolysis a production matrix, called the father, is metallized.

Through the same method a negative or mother plate is made which can produce additional safety copies of the father. These matrixes are called sons. Granulate is formed to a disc including the information on it. During the injection moulding process, the discs go from granulate to disc. Thermal processes and extreme accuracy ensure optimal 'pit definition', the optimal transfer of information from the matrix to the disc. Next an 800 Angstrom layer of aluminium is applied to the surface so that the laser can read the information. To protect this fine aluminium layer, a carefully measured amount of coating is applied while the CD spins rapidly, ensuring even application of the coating.

Discs are then given labels or a photograph in up to six colors. Finally, each disc is automatically provided with printed matter, packaged and sealed. Special options are, of course, available at this step.

How Does A CD Work?

A CD is 12 centimeters / 4.75 inches in diameter and 1.2 millimeters thick. It consists of a transparent polycarbonate bottom layer, a reflecting aluminium layer and a protective coating. The reflecting surface of the disc is divided into small pits surrounded by higher areas. This forms the information. To read this information we need a light source; a small laser beam. By way of a prism and a few lenses the laser beam can be focused very precisely on the reflecting surface of the disc. The bundle of lights is discontinuously reflected, and each portion of reflected light is transposed into a wave which can be read as a piece of information.

All the pits are organized in a single spiral called the track, and if you follow this track very, very fast, you've got a compact disc with audio, video or computer data. The protective coating protects the information from mechanical destruction. Scratches and dust on the substrate site of the disc are out of focus for the light beam, while the light beam guides itself to follow the track very precisely. This track is so tightly rolled up that on one CD it's up to 6 kilometers or 3.75 miles long.