Disadvantages Of Compact Disc

Raw Materials

A compact disc is a deceptively simple looking device considering the technology required to make it. CDs consist of three layers of materials:

1 A base layer made of a polycarbonate plastic.

2 A thin layer of aluminium coating over the polycarbonate plastic.

3 A clear protective acrylic coating over the aluminium layer.

Some manufacturers use a silver or even a gold layer instead of the aluminium layer in the manufacture of their compact discs.

Design

The compact disc is designed strictly according to the standards established by Sony and Philips in order to maintain universal compatibility. A CD is 4.72 inches (120 mm) in diameter and .047 inches (1.2 mm) thick. The positioning hole in the middle is .59 of an inch

The glass is polished to a smooth finish and coated with a layer of adhesive and a layer of photo resist material. The disc is approximately 9.45 inches (240 mm) in diameter and 24 of an inch (6mm) thick. After the adhesive and photo resist are applied, the disc is cured in an oven. 3 Next, both the pre-master tape and the disc master are put into a complex laser cutting machine.

The machine plays back the audio program on the pre-master tape. As it does so, the program is transferred to a device called a CD encoder, which in turn generates an electrical signal. This signal powers a laser beam, which exposes or "cuts" grooves into the photo resist coating on the glass disc (the disc master). 4 The grooves that have been exposed are then etched away by chemicals; these etched grooves will form the pits of the CD's surface. A metal coating, usually silver, is then applied to the disc. The disc master now contains the exact pit-and-land track that the finished CD will have.

this stage. Next, the disc is scanned for flaws such as water bubbles, dust particles, and warps. If a flaw is found, the disc must be discarded. 11 If the disc meets the quality standards, I it is then coated with an extremely thin, reflective layer of aluminum. The coating is applied using vacuum deposition. In this process, aluminum is put into a vacuum chamber and heated to the point of evaporation, which allows it to be applied evenly to the plastic disc. 12 Finally, a clear acrylic plastic is applied to the disc to help protect the underlying layers from physical damage such as scratches. After the label is printed, generally using a silk-screening process, the compact disc is complete and ready for packaging and shipment.

Quality Control

A compact disc is a very precise and accurate device. The microscopic size of the data does not allow for any errors in the manufacturing process. The smallest of dust particles can render a disc