COMPACT DISC - CD
Compact disc - CD
The CD (Compact Disc) was developed to meet the requirements of the market for a system of original
sound reproduction capable of being used over and over maintaining quality unaffected. An optical
system that doesn’t require friction or direct contact with the recorded material was accomplished,
different from magnetic tapes or vinyl discs that reproduce sound by means of a pick-up device which is
in permanent contact with the recorded layer.
What’s a Compact Disc?
A disc manufactured from optical grade polycarbonate (plastic resin), on which tiny salient called PITS
were created forming a continuous spiral, beginning from the center towards the outer edge of the CD,
called TRACK. A protective lacquer is applied over the pits and track in order to avoid the covering and
creation of new pits. These tracks are digital information covered by a reflective layer in order to enable
the laser beam of the players to read said information.
>> Cross Section of a CD
UV Ink
Lacquer
Aluminum
1.2 mm
.15 um
Polycarbonate Resin
Pit
>> This figure shows the spiral shape of the track
Grupo Laser Disc . Leaders in Replication of Compact Disc and DVD . www.grupolaserdisc.com . © 2006
COMPACT DISC - CD
General Features
The CD has a diameter of 12 cm, and an inner circle of 15 mm. The digital information is stored in the
area that starts at 25 mm from the center and it goes up to 58 mm. In the borders of this area there are
two rings, an internal one that contains the table of contents of the disc (LEAD IN), allowing the laser to
synchronize and recognize the contents of the audio and data information before reproduction. The
length of the disc is directly related to the dimensions of the table of contents, that can store 74 minutes
of audio and a maximum of 99 tracks. The outer ring (LEAD OUT) has a width of 1 mm and determines
the end of the data stored.
Inner guide
23 mm 25 mm
15 mm
Data area
120 mm
58 mm
>> General Features
Outer guide
The CD has a diameter of 12 cm, and an inner circle of 15 mm. The digital information is stored in the
area that starts at 25 mm from the center and it goes up to 58 mm. In the borders of this area there are
two rings, an internal one that contains the table of contents of the disc (LEAD IN), allowing the laser to
synchronize and recognize the contents of the audio and data information before reproduction. The
length of the disc is directly related to the dimensions of the table of contents, that can store 74 minutes
of audio and a maximum of 99 tracks. The outer ring (LEAD OUT) has a width of 1 mm and determines
the end of the data stored.
Grupo Laser Disc . Leaders in Replication of Compact Disc and DVD . www.grupolaserdisc.com . © 2006
COMPACT DISC - CD
Replication
The Replication Process is composed of the following stages:
1 :: Preparation of stamper.
In order to be placed in the replication line.
2 :: 2. Molding of disc by injecting the polycarbonate resin.
The material is melted and injected at high pressure against the stamper.
Before the substrate is removed from the injection machine, it has to be rapidly cooled, this takes almost
4 seconds per unit.
Once it has been removed, the substrate is still transparent and the information can’t be read.
3 :: Sputtering.
A thin metal layer must be applied in order to create the reflective surface.
4. Lacquering
The reflective layer is protected by applying a protective layer of lacquer. This lacquer is cured
by exposition to UV light.
5. Inspection
Every disc is carefully inspected in-line, this means that the equipment automatically separates
the scarp material. Then digital and disc signal analysis are performed.
6. Artwork printing
The last step is the printing of the artwork. Each disc is monitored by a high resolution camera.
Grupo Laser Disc . Leaders in Replication of Compact Disc and DVD . www.grupolaserdisc.com . © 2006