

TAKING THE MYSTERY OUT OF MANUFACTURING, PART I

by Dana J. Parker

Many potential publishers of CD-ROM are unclear about the CD 
manufacturing process. Even for many experienced CD-ROM 
publishers, the mastering and replication plant is a black box: they 
put their data and their money in, and they get discs out. 

The CD manufacturing process is perhaps more concerned with 
standards than any other element of creating a CD-ROM title. In 
addition to the standard physical and logical formats, there are 
particular criteria to ensure that each disc meets or exceeds certain 
quality standards. Manufacturers must stay within given parameters 
of specific levels for BLER (Block Error Rate), flatness (skew), 
reflectivity, and birefringence. (Birefringence, also called double 
refraction, occurs when a light wave breaks into two perpendicular 
waves upon entering the clear polycarbonate. A birefringent disc 
would scatter laser light and be very difficult to read). 

It's just not that simple to create thousands and thousands of discs, 
each with billions of pits, each pit as small as 500 hydrogen atoms 
laid end-to-end, and maintain an uncorrectable error rate of fewer 
than one in 20,000,000 discs. The manufacture of a CD can be 
broken down into 5 steps: Premastering, mastering, electroforming, 
injection molding, and spin coating and printing.

Physical Properties of the Compact Disc

Compact discs are 12 centimeters (4 3/4 inch) in diameter, just over 
a millimeter thick, and weigh about half an ounce. A disc's physical 
composition consists of clear polycarbonate, a very thin layer of 
aluminum, and a lacquer protective coating. A CD-ROM disc can 
hold up to 680 MB of data: text, images, graphics, sound, video, 
and animation. Data is stored in the form of microscopic pits 
arranged in a single spiral track. A pit is about a half-micron wide -- 
about the size of 500 hydrogen atoms laid end-to-end -- with a 
single CD-ROM containing approximately 2.8 billion pits. The 
spiral track makes 20,000 or more revolutions around the disc. 

CD-ROM Premastering

Data to be published on CD-ROM may arrive at the manufacturing 
plant in many different formats. Among the most common are 9 
track, 8mm Exabyte, and DAT tape, but many mastering facilities 
also accept MO (magneto optical) cartridges and SCSI hard drives.
Before this data can be used to create a compact disc, it must be 
converted into the correct format for CD-ROM, CD-I, CD-ROM 
XA, or CD Video. Also, EDC/ECC (error detection code/error 
correction code) must be added where necessary. Increasingly, data 
arrives already recorded in its final CD format, complete with error 
detection/correction, on CD-Recordable media. U-matic or 8mm 
tape or CD-R discs can be used as input for the next step, which is 
the creation of a glass master.

Mastering

Mastering is the process of using an LBR (Laser Beam Recorder) 
to etch the audio or computer data, in the form of microscopic pits, 
into either a layer of photoresist or plastic on a glass master disc, 
which is then electroplated with silver or nickel to form a metal 
stamper. Photoresist and Non-Photoresist are the two most common 
methods, although direct metal mastering is under development.

Photoresist mastering requires several steps. First, a highly polished 
glass disc is coated with adhesive and an even layer of photoresist, 
and then baked, to "cure" the photoresist.  Then the photoresist is 
exposed to the laser beam, which etches a pattern of pits and lands 
into the photoresist layer. The glass master is then "developed" in a 
chemical bath, which cuts away areas exposed to the laser beam. 
Finally, a metal coating is evaporated onto the etched, developed, 
photoresist layer. At this point, the master can be tested on a master 
player. This method is very difficult and time-consuming with many 
critical steps and stringent humidity, temperature, and air quality 
requirements. Despite the difficulties of this method, it produces 
very high quality masters and is used in most plants. 

NPR (Non-PhotoResist), also called DRAW (Direct Read After 
Write) mastering, also starts with a glass master, but the glass is 
coated with a layer of plastic, which is then vaporized in a pattern 
of pits and lands by the LBR. A reading laser follows the cutting 
laser to check the integrity of the cut directly after it is made. This 
method eliminates the chemicals used in adhesive and photoresist, 
and the baking and development processes, as well as the necessity 
for a master player to test the disc. Masters can be created two to 
three times faster than with the photoresist method, and any errors 
can be detected immediately, rather than an hour or two after the 
process begins. The NPR process assures improved efficiency, 
yield, and productivity over photoresist mastering and is more 
environmentally friendly. As in photoresist mastering, the final step 
is to evaporate a metal coating onto the etched layer of plastic. The 
metal layer makes the glass master electrically conductive.

Electroforming

Once the glass master has been written, tested, and silvered, it is 
ready to be electroplated. The now electrically conductive disc is 
placed in a reservoir holding an electrolyte solution (nickel 
sulphamate) and electrical current is applied at a low level and 
gradually increased, producing a metal part of sufficient thickness 
in about two hours. If the number of  replications of this particular 
disc is expected to be 10,000 or less, this nickel copy, called the 
metal "father," can be used as a stamper to replicate CDs. 
Otherwise, the metal father is returned to the electroplating process 
to create metal "mothers," which are in turn used to generate metal 
"sons," which are the stampers used in molds to replicate CDs. 
Often, the metal "family" is stored for future reorders. Glass 
masters can be washed and reused many times.

It's important to note that not all CD manufacturers own their own 
mastering and electroforming equipment. Many newer and smaller 
plants do only the mass replication of discs -- that is, the injection 
molding, metalizing, printing, and packaging of discs at their own 
plant. They must buy mastering from other, larger plants, which 
involves sending their customer's data to another plant to be 
transferred to a glass master and then to a metal father and/or 
stamper. The stampers are returned to the originating plant, where 
they are used to mass-produce discs.

Replication

Injection molding techniques are most commonly used to stamp out 
thousands of copies of a disc in polycarbonate. Polycarbonate was 
chosen because of its transparency, dimensional stability, impact 
resistance, and freedom from impurities. Polycarbonate, in the form 
of pellets, is heated to about 350 degrees centigrade in order to 
achieve smooth flow properties when injected into mold cavities. 
Metal stampers created in the electroforming process are carefully 
mounted to form one side of the platter-shaped mold. The molds 
themselves are finely machined so that the resulting disc is flat, 
centered, and free of optical distortion and impurities. Because the 
molded polycarbonate would harden slowly at room temperature, 
water channels are carefully designed as part of the molds so that 
the formed disc can be cooled and hardened quickly and evenly. At 
this stage of the process, the compact disc is a clear plastic platter 
with microscopic pits molded into one side.

Metalization, Spin Coating, and Printing

In order for the disc to be readable by a laser beam, it must reflect 
laser light. Four metals are inert to polycarbonate and have 
sufficient reflective properties to be used as a reflective   layer: 
gold, silver, copper, and aluminum. Aluminum is the most cost-
efficient, and most widely used, although CD-R discs use gold for 
its greater reflectivity. Some plants offer gold metalizing as an 
option for commemorative discs and limited runs. An extremely 
thin layer of metal (50 to 100 nanometers) can be applied to the 
plastic disc via vacuum evaporation, sputtering, or wet silvering. To 
protect the metal from scratches and oxidation, a thin layer of 
acrylic plastic is applied by spin-coating and cured in ultra-violet 
light. The molded, metalized, spin-coated disc can now be silk 
screen-printed in up to six colors, or labeled with a special non-
impact offset printing process. The disc is now finished and ready 
to be packaged and shipped. The time from raw polycarbonate to 
labeling is under two minutes, and a single replication line is 
capable of producing two million discs per year.

Packaging

There are now as many ways of packaging a CD as there are types 
of content on CD - too many to name or describe here, with new 
and innovative ideas in packaging becoming reality every day. The 
single most popular packaging for CDs of all types remains the 
jewel case - a clear plastic hinged case with slots for tray cards and 
booklets. The jewel case, though not cheap - usually about 25 cents 
each - remains a popular and inexpensive packaging option because 
the insertion of discs and printed matter into jewel cases can be 
automated, and most disc manufacturers own the equipment. Other 
types of packaging - plastic and paper sleeves, for example - 
require that the disc be inserted by hand. Even in the most 
automated and high-tech plants you can find workers seated around 
tables stuffing discs in sleeves. Normally, each motion necessary to 
insert the disc and printed matter is billed separately. If it takes five 
separate and distinct motions to assemble a disc in a sleeve with 
printed matter, the charge will be as much as 20 cents per disc. 
Even if the packaging itself costs less than a jewel case, using 
manual labor can make it more expensive. 

(Standard Deviations column, CD-ROM Professional magazine, 
September/October 1994. Contributed by author. May be 
reproduced with attribution given.)


TAKING THE MYSTERY OUT OF MANUFACTURING, PART II

By Dana J. Parker

Look beneath the surface; let not the several quality of a thing nor 
its worth escape thee.

Marcus Aurelius [Antoninus]   121-180
Meditations, VI, 3

So, you've spent many months and thousands of dollars creating 
your CD-ROM application. You've designed packaging, tray cards, 
and label art. You've decided how your product will be marketed, 
distributed and supported. You've shopped around, gotten pricing 
from several replicators, and chosen one who can meet your needs 
at a rock-bottom price, and according to your schedule. You're 
ready to commit all that work to thousands of polycarbonate discs.

How can you tell if the CD-ROM replicator you have chosen 
makes good quality discs?

What You Can't See Can Hurt 

Getting the right data on the disc, with the right label, and in the 
right packaging, is what most CD-ROM publishers are 
concerned with. It's often assumed that quality in disc 
manufacturing is a "given"; that is, if the disc is good, it will 
look right, and it will work. It's further assumed that a bad disc 
won't make it out of the plant into your customers' hands. Many 
CD-ROM publishers assume that every disc has been 
completely tested. Others ask about "BLER" (Block Error Rate, 
see sidebar) and are reassured when the salesperson cites a low 
figure.
	
The fact is that in every part of the manufacturing process, from 
premastering to packaging, there are many things that can go 
wrong. Some of these manufacturing errors, like a poorly printed 
label or pinholes in the aluminum reflective layer, are visible. Most 
are not. Without stringent testing procedures and quality control, 
cumulative minor errors in every part of the process can add up to 
an unreadable disc, or a disc that works on some drives but not 
others, or a disc that works right out of the box, but which 
degenerates and becomes unreadable over time. Marginally 
defective discs can also increase random access times. BLER, by 
itself, is actually a poor indicator of the quality of a disc, because 
the error detection and correction in CD-ROM drives can overcome 
many manufacturing errors that are not accounted for by BLER. A 
disc with a low BLER rate, but with other tolerances at the high end 
of the scale, can succumb rapidly to environmentally introduced 
impediments such as dust, dirt, scratches and fingerprints. Worst of 
all, even a disc that is nominally up to spec may be unreadable on 
some low-end drives, even though it is functional on others.

A Disc is a Disc...Right?

The very nature of CD-ROM manufacturing makes quality control 
as difficult as it is important. The average CD-ROM replication run 
is 1,000 to 1,500 discs. Once the stamper has been placed into the 
mold, discs can be molded at a rate as high as 15 discs per minute 
(900 discs per hour). By the time a disc pulled out of the process 
near the beginning of the run has been tested, the entire run could be 
molded and ready for labeling. If there's a serious problem, the 
entire run might have to be discarded. This is time-consuming and 
costly. In some cases, manufacturers will label and ship marginal 
discs, and hope that nobody notices. 

Most CD-ROM manufacturers started out as CD Audio 
manufacturers. For many, as much as 90% of their business still 
consists of CD Audio discs. Because CD Audio discs sell for 
considerably less than CD-ROM discs, because the content of CD 
Audio discs is only music played in a stream, and because it is far 
easier to mask error in audio playback than it is to correct errors in 
computer data, CD Audio discs are subject to less stringent 
specifications than CD-ROM discs. Some manufacturers 
manufacture only CD-ROM, some dedicate molding lines to CD-
ROM, some use higher testing standards for CD-ROM discs, and 
some make and test CD-ROM discs to the same specs as audio 
discs. One manufacturer recently told me, when I asked what extra 
quality control measures they used for CD-ROM, "A disc is a 
disc". Obviously, this is not the kind of manufacturer you want to 
handle your CD-ROM replication needs.

How to Make Sure that What Can Go Wrong, Doesn't

Finding a replicator who shares your concerns about quality is only 
part of the solution. There are steps you can take to make sure that 
what you want is what you get. 

Labels and Printed Material: First, make sure that what you order is 
what you want. If the manufacturer provides templates and 
specifications for label art and printed material such as tray cards 
and booklets, use them. Submit your color separated films as 
specified, with colors denoted as PMS (Pantone Matching System) 
colors. If you have questions, ask to speak to the graphics 
department. Make sure any inserts are noted on the order form, or 
your disc may well be shipped without them. If the dimensions of 
the tray cards you have printed are even slightly out of spec, they 
can jam the machinery that inserts them into jewel cases. Use a 
printer that can ensure conformance to specs, or have the disc 
manufacturer take care of your printing needs for you. 

Premastering: With the increasing use of CD-Recordable discs as 
input, the possibility of errors being introduced into the actual data 
that goes on a disc is minimized - as long as the CD-R disc itself is 
free of defects. Using flawed CD-R media as input ensures that 
these flaws will be faithfully reproduced in CD-ROM. However, 
some manufacturers still do not use the CD-R disc you send in as 
direct input to the LBR that creates the glass master. Instead, they 
transfer the data from your CD-R  to tape, which is then used as 
input. Most plants do a bit-for-bit verification to ensure that what 
you send in is what you get out. 

Make sure that the data on the CD-R disc you send to the plant as 
input is exactly the way you want it. Use a "virgin" PC, in the 
minimum configuration required for your application, and a low-
end CD-ROM drive, to test the installation and features one last 
time. Unfortunately, all low end drives are not created equal - what 
works on one may not work on another. This is all the more reason 
that your discs should be manufactured well within all specs - to 
allow for factors that are beyond your control, such as your end-
user's equipment.

Use a program such as Disc Detective to check the integrity of the 
CD-R disc that you plan to send in as input. Even if the disc plays 
without any noticeable errors, Disc Detective can, in some cases, 
find flaws in the CD-R media that could be reproduced in the mass-
produced discs.

Finding a Manufacturing Partner

The electrical, mechanical, and chemical processes involved in 
manufacturing compact discs are incredibly complex, and methods 
used to test the resulting discs are equally complex. 

For example, a CD pit is one of the smallest manufactured 
formations, about the size of a smoke particle. You can't even see 
them without using a scanning electron microscope. And yet, 
minute distortions in the dimensions of  the pits -- their depth, form, 
and length -- can make the difference between a good disc and a 
marginal one. Defective pits can be the result of contamination, 
vibration, chemical properties of materials in the mastering and 
galvanizing process, ambient temperature, humidity, injection 
pressure, temperature of the molten polycarbonate, temperature of 
the mold, chemical properties of the polycarbonate, uneven cooling, 
shrinkage, and so on. And that's just the pits (pun intended). Moving 
on to tracks, there's track pitch, eccentricity, beginning and end of 
data area, and so on. Then there's reflectivity, optical properties, 
flatness (skew), and overall disc dimensions including weight, 
thickness, and clamping area. 

In a production facility, finished discs are inspected for continuous 
and random defects such as birefringence, high-frequency signal, 
frame error rate, crosstalk, jitter, noise, presence of foreign 
particles, reflectivity, frame tracking, number of interpolations, and 
skew. The results of the tests can then be interpreted and used to 
fine-tune the myriad factors in every step of disc production. 
Unfortunately, it's not as simple as looking at the results of the ECC 
test (see sidebar) and then mounting the stamper just a teensy bit to 
the right - there many factors that could result in off-center tracks. 
A misplaced stamper could also produce a disc that compensates 
for errors found in the stamper itself.

Obviously, you shouldn't have to know or think about all of the 
things that can go wrong when your discs are being manufactured. 
That's the manufacturer's responsibility. Unfortunately, there is no 
agency or study currently available that monitors the quality of 
product each plant manufactures. Philips, the licenser of the 
standards and the specifications that are used to measure the quality 
of the discs in various formats, does not subject their licensees to 
any kind of testing to ensure that they are complying with the 
standards. However, there are still some things you can do to make 
sure you get high-quality discs.

Ask your mastering and replication facility about their test 
equipment and their testing procedures. It's not enough that they 
own all of the latest and most expensive test equipment; they should 
also be able to tell you how they use it in a specific Quality Control 
program. Can they show you a Quality Control Procedures 
Manual? Do they test one disc from the beginning, middle, and end 
of each run? Do they pull a sample disc from every line once an 
hour for testing? More important, do they simply test the discs to 
see if they are "good enough", or do they track the results of these 
tests as an ongoing attempt to locate trends and correct them before 
a serious problem arises? Are they ISO 9000 compliant, are they at 
least working on it, or have they never heard of it?

Does your disc manufacturer have separate, and more stringent, QA 
procedures for CD-ROM? Do they have a computer available that 
is capable of playing your disc? If you receive a bad disc or 
shipment of discs, will your replicator test them for you at no 
charge and take steps to correct the problem, as well as replace 
your discs? Although your sales representative may not be able to 
answer these questions immediately, he or she should certainly be 
able to find the answers for you, or put you in touch with someone 
who can. In any case, your salesperson should take your concerns 
about quality seriously.

No CD-ROM manufacturer makes perfect discs, just as no 
automobile manufacturer makes perfect cars. Some manufacturers, 
however, consistently do a much better job than others. While many 
CD-ROM publishers insist that their priorities for choosing a 
replicator are quality, service, and price, in that order, the typical 
CD-ROM publisher will devote hours of time and effort to find the 
lowest price, fastest turn time, and friendliest and most helpful 
customer support, but will worry about quality only when their 
current manufacturer screws up - and when it's already far too late.

*******************Sidebar********************* 
The following parameters are more stringent for CD-ROM than 
they are for CD Audio:

BERL: Burst Error Length should be less than 5 for CD-ROM. 
Shows physical damage such as scratches, dirt, etc. Indicates 
presence of a physical defect large enough to affect more than one 
block of data.

BLER: Block Error Rate should be no more than 50 errors per 
second for CD-ROM. Measures the number of blocks of data that 
have at least one occurrence of erroneous data; i.e., rate of errors 
per second. 

ECC: Eccentricity should be *50* for CD-ROM. Measures the 
difference between the geometric center of the tracks and the center 
of the center hole. If this figure is higher than *50*, random access 
time increases.

MID: Maximum Information Diameter should be less than 113mm 
for CD-ROM. Technically, MID signals the end of the disc.

SYM: Symmetry should be 10% deviation for CD-ROMs.

(Standard Deviations column, CD-ROM Professional magazine, 
November/December 1994. Contributed by author. May be 
reproduced with attribution given.)

Dana J. Parker is Standards Columnist and Contributing Editor for 
CD-ROM Professional magazine, and the co-author of  New 
Riders' Guide to CD-ROM, Second Edition, New Riders 
Publishing, CD-ROM Fundamentals, Boyd & Fraser, and CD-
ROM Professional's CD-Recordable Handbook, Pemberton Press. 
Communications to the author may be addressed to CIS 
102212,472.



