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DVD
Replication
All DVD discs are
made of two parts, each half the thickness of a CD; that is, each part
is 0.6 mm thick. The two parts are bonded together, producing a disc as
thick as a CD (1.2mm).
As in CD replication,
DVD replication begins with a flat glass disk covered with photo-resist
material.
DVD-9 and DVD-18 discs contain data in two layers; one of the layers is semi-reflective, allowing the playback laser to read the data on both layers in sequence. Both layers are read by a laser from the same side.
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The
replication process for DVD is essentially the same as that for CD,
except with much closer tolerances and some extra steps. There are also
some differences in replication depending on the type of DVD disc being
made: DVD-5, DVD-9, DVD-10 or DVD-18.
Thus,
two pressings are needed to make one complete disc. DVD-5 and DVD-9
discs, which have data on only one side, consist of one part with data
and one blank part.
As
the disc spins, a laser beam modulated according to the information on
the DLT tape "writes" the data onto the disc by creating
chemically-etched pits. Family names are often used to describe the next
steps in the process.
By
electroplating, a metal negative to the glass disc is produced; the
metal disc is called the "Father." Again by electroplating, a
positive-image "Mother" disc may be made from the Father
stamper, and negative-image "Sons" are plated from each
Mother.
The
Father and the Sons are then placed in molding presses. Melted plastic
is poured over the Father and Sons and allowed to cool. (As compared
with a CD, DVD discs need a shorter plastic-injection time and a higher
molding temperature.)
The
disc is then finished by applying a reflective layer, protective
lacquer, and labeling.
