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| Hybrid
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Super
Audio CD |
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Hybrid disc structure
(cont.)
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Manufacturing
method
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Like
for dual-layer DVD, SACD is made of two
polycarbonate substrates, each of 0.6mm thick, in
order to present the same total thickness as
conventional CDs. The upper layer is injunction
moulded to form the pits and flats of the Red Book
audio data, while the second layer is moulded in a
much thinner way in order to include much more data
than for CD (4.7GB instead of 780MB), in other
words, more channels of high-resolution music, not
to mention text, graphics, video,...
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Comparison
of disc structures for CD, SACD and DVD
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The
CD layer is then treated like for conventional CDs :
it is coated with a highly reflective metal layer,
then a protective layer, and finally the screen
printing which will be visible on top of the disc.
The high-density layer is treated with a semi-transmissive
coating, which allows the CD laser to go through and
reach the upper CD layer, while a SACD laser will
focus on the high-density data's pits and flats.
Then, the two substrates are bonded together back to
front by an optical transparent bonding method (UV
bonding).
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Hybrid
disc manufacturing process flow
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Homogeneity
of the semi-transmissive layer, which is the most
critical parameter for hybrid disc manufacturing, is
guaranteed by standard sputtering equipment in use
for dual-layer DVD discs.
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