A Beginner's Guide to the Internet/INTERNET.ISO/text/faqs/romart.txt

Text File | 1995-04-08 | 12.7 KB | 280 lines

HOW CD-ROM Discs are Made

by Lorri Haney
Marketing Manager Nimbus Information Systems


CD-ROM is fast becoming one of the most important tools of this century.
As the compact disc format for computers grows in acceptance, an
increasing number of software publishers have found themselves venturing
into the brave new world of CD-ROM, taking advantage of its unprecedented
capacity and options for information delivery.  Yet for many publishers,
the production process of physically manufacturing a compact disc is
still a mystery, full of complicated technology and foreign terminology.
In reality, the world of CD-ROM manufacturing is highly technical and
complex, but like other elements of software production, such as printing
and packaging, it is a step-by-step, incremental process.

The first step in CD-ROM manufacturing, is receipt of the publisher's
software application.  Most replicators can accept your project as either
raw computer files or pre-formatted CD image files on input media ranging
from CD-Recordable and  SyQuest cartridges, to older backup media such as
9 track tapes.  CD-Recordables or "CD-Rs" have become a  popular source
media because of their ability to provide publishers with a working CD
prototype before going to large scale replication.  Supplying a CD-R also
means that data is "CD ready" for manufacturing, thus eliminating the
need for further formatting. The growing affordability of desktop CD-
Recordable technology has given rise to a growing multitude of service
bureaus (including almost all replicators) who offer this service
inexpensively.  It  has also allowed many publishers with a large number
of new titles to justify bringing the work in-house.


Premastering

If raw computer files (those not yet formatted for CD) are submitted,
information must go through a pre-production step called premastering.
This process involves converting files into a standardized, logical
format required for compact disc manufacturing. This standardization
ensures universal readability of any CD-ROM disc, created for a given
platform, by all CD-ROM drives. ISO 9660 is the international standard
for the CD-ROM logical format in that it can be universally read and
interpreted on Mac, PC, UNIX and VAX platforms.  Apple HFS (Hierarchial
File System) formatting is specifically designed to support the custom
features of the Macintosh operating environment on compact disc.  Other
CD data formats available to publishers are CD-I (Compact Disc
Interactive), CD-XA (Compact Disc Extended Architecture -- a mixed mode
format where data and audio files are interleaved) and hybrid formatting
which allows multiple file systems (such as ISO and HFS) to be placed on
a single, shared CD-ROM.

During premastering, a bit for bit verification is usually also performed
to insure error-free conversion.  Once the logically formatted data is
approved, manufacturing can begin.  Disc manufacturing involves five
steps including mastering, electroforming, replication, printing and
packaging.


Mastering

Since the quality of any CD-ROM disc is only as good as the master used
to create it, mastering is considered the most critical step in the
manufacturing process. CD pits, created in the mastering process, are
among the smallest of all manufactured formations -- each is about the
size of a particle of smoke.  Which means that even the most microscopic
forms of contamination can obscure large amounts of data.  A clean room
environment, where the size and number of particles in the air are
strictly controlled, is therefore, a key requirement in both mastering
and manufacturing CD-ROMs.

Although there are several methods currently available for CD mastering,
a photoresist system is most commonly used.  This method produces a glass
master by applying a photoresist (a light sensitive chemical that acts
similarly to emulsions used to print black and white photos) to a
specially prepared glass substrate. The photoresist is generally applied
in a spin coating process in a thickness equal to approximately 1/8th of
a micron; 640 times thinner than a human hair.  Data is recorded in the
photoresist layer through a laser encoding process where a computer
translates the formatted input media into a series of  "on" and "off"
pulses of a laser beam recorder.  In a spiral track, the laser beam
recorder exposes portions of the photoresist with a blue light, creating
the disc contents.  If stretched linearly, this spiral track can run as
long as three miles from the inner hub to the outer edge of the disc.
Much like a photographic process, the glass master is then developed by
applying a chemical developing fluid.  The exposed areas of the
photoresist are etched away resulting in the formation of millions of
microscopic pits in the resist surface.  After developing, a metal
coating, usually silver, is evaporated onto the photoresist surface to
provide a conductive surface for electroforming the glass master.


Electroforming

The ultimate goal of electroforming is to generate metal stampers used to
replicate CDs.  In this stage of production the glass master, which is
now electrically conductive with its silvered surface, is submerged into
a chemical bath containing nickel ions.  By running current through an
electrical circuit, nickel ions are attracted to the exposed surface of
the glass master containing the disc image.  As this coating of nickel
grows, it conforms to the contours of the pits and lands (the space
between pits) etched in the exposed photoresist surface.  The end result
is the formation of a thick, durable piece of nickel plating containing
a negative impression of the compact disc in its metallic surface. This
initial piece of metalwork is known as a metal master or "father".  It is
called a father because it is used to generate a family of two additional
pieces of metalwork called a mother and a stamper.  Mothers and stampers
are successively grown in additional electroforming processes; mothers
from fathers and stampers from mothers -- each piece an opposite image of
the other.  The stamper, an exact replicate of the metal master, is the
end product of this stage of production and the "metal template" from
which plastic CD replicates will be mass produced.


CD Replication

The first step in replication is to transfer the image of the compact
disc from the metal stamper to a plastic substrate. A high-precision
injection molding press injects a molten resin made of optical grade
plastic into a mold cavity, containing the stamper on one of its faces.
This process, which takes only a few seconds, results in the formation of
a clear plastic disc with the pits impressed on one side. The plastic
substrate is then metalized by applying a very thin layer of pure
aluminum over the data pits molded into its surface. This metalization
process provides reflective surface required for disc playback and gives
the CD its distinctive, mirror-like appearance.  A typical method of
metalizing is through a sputtering process where discs are individually
bombarded with aluminum atoms providing a uniform coverage.  A final step
in manufacturing is the application of durable lacquer coating on top of
the aluminized surface.  This coating protects the aluminum from
scratches, oxidation and provides a platform for label art printing.


Printing and packaging

Graphic images are applied to the lacquered disc surface via high speed
silk screening or offset printing.  Depending on your replicator's label
printing capabilities, artwork incorporating as many as 8 colors can be
reproduced.  Silkscreen printing, the most widely used method, involves
transferring artwork to a porous screen through which inks are applied in
a process similar to stenciling. Offset printing, which uses ink rollers
and printing plates to transfer images, is widely used in traditional
commercial printing and now also available for compact disc labels.
Offset printing allows for the reproduction of images with higher quality
resolution; its benefit over silkscreening is its ability to produce
enhanced 4-color process images and other complex graphics.

After printing, discs are either automatically or manually packaged.
Although there has been growing availability and use of alternative
options, the plastic jewel case remains the most commonly used packaging
choice for CD-ROM.  This trend has emerged due to its durability and
universal availability of automated assembly.  Other popular packaging
options, which may require manual assembly depending upon the option and
replicator,  include lightweight alternatives such as TYVEK and cardboard
sleeves, transparent plastic sleeves such as Viewpaks, and
environmentally-friendly cardboard versions of jewel cases like DIGIPAKs,
and ECOPAKs.


Quality Control

Disc quality is strictly controlled at every step of production to assure
conformity to industry specifications.  This ensures that all disc
tolerances, which are acceptable ranges of variance, are within the
design limits of all CD-ROM drives. Although all CD-ROM disc
manufacturers are governed by the universal quality standards set forth
by Sony and Philips in the Yellow Book specifications (the standards
document for ROM), each manufacturer typically has their own quality
control philosophy.  The best replicators have internal standards which
go beyond industry requirements. In mastering and replication critical
parameters include signal quality measured by Block Error Rates --
commonly known as BLERs, adherence to electronic standards, material
stress and other physical defects that can affect disc playability.


Turnaround time

Turnaround time, also known as turn time, is the time it takes for a
replication facility to complete all the stages of CD-ROM production
mentioned above.  The faster the turnaround required for finished
product, the more expensive the service.  Rush jobs, such as one- and
two-day turns, are available but at significantly higher costs than
standard seven-day turns, with premiums varying among manufacturers. Turn
time can be a confusing issue for publishers, because CD-ROM replicators
often vary in their definition.  Some quote strictly on a business day
basis, while others quote based on calendar days.  Some consider the day
data arrives at the plant day zero and do not apply it to days quoted in
a turn, and others consider it day one.  The best strategy for a
publisher obtaining quotations based on a given turn time, is to clarify
each replicator's definition to ensure an apples to apples comparison.
It is also important to note that CD-ROM production is a scheduled,
multi-faceted manufacturing process which involves more than just
pressing discs.  A quoted turn time is a promised date based on the
assumption that all required parts including data, disc artwork and
packaging materials are "workable" and at the factory at the necessary
time.  Any delay in receipt of workable parts, such as print which
arrives late or label art which is out of the manufacturer's
specification, will usually add critical days to turnaround time.  While
some manufacturers will go to great lengths to meet delivery deadlines
under less than perfect conditions, their ability to do so depends upon
several critical factors such as the nature of the delay, operating
capacity and their own in-house capabilities.

As the CD-ROM software industry grows, so does the demand for superior
disc replicators.  Although disc manufacturing is a standardized process,
the quality of your total CD-ROM production experience, including
flexible scheduling, technical expertise and one-stop-shopping to name a
few, can vary greatly from company to company. Finding the right long
term partner to meet your requirements is a task which involves research
beyond basic price comparisons.


Lorri Haney
Marketing Manager, Nimbus Information Systems

As marketing manager for Nimbus Information Systems, Lorri Haney is
responsible for CD-ROM strategic marketing and technical communication
programs.  Her background prior to Nimbus includes an MBA in marketing
and extensive experience in high technology marketing management for
industries including telecommunications and database publishing services.

For those readers interested in viewing the manufacturing process, a
multimedia tour on CD-ROM for Macintosh and Windows platforms is now
available.  Call Lorri Haney, Marketing Manager at [phone] x457 to
receive your free copy.