Moulding Process Optimization for Optical Media ... - DaTARIUS

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Moulding Process Optimization for Optical Media:
Improving quality and reducing costs by Thomas Moosbrugger,
Optimization Product Manager, DaTARIUS Group
For media manufacturers, a key goal in today’s ever more competitive market is to achieve the
highest possible manufacturing yields in the shortest process time, while maintaining a high –
and consistent – standard of quality. With cycle times of under 3 seconds for DVD, being able to
optimize the process overall is increasingly vital if disc quality is to be kept within specification.
As production run lengths can often be short – and are continually becoming shorter – an
essential element in attaining high yields with high quality is a rapid return to a stable process
and making useable discs following stamper changes. Another, often neglected, factor in
manufacturing is the cost associated with production line maintenance, which contributes to the
ability to come back on-line, following any shut downs, without major equipment malfunction.
Mould temperature regulation directly affects various parameters that need to be carefully
controlled in order to keep discs within specification, and achieve the shortest cycle times.
These parameters include Birefringence, Dishing, HF and Jitter.
High Birefringence values, which cause the player laser beam to be scattered and can give poor
playback, are caused by uncontrolled or rapid polycarbonate shrinkage after cooling.
FIGURE 1: Birefringence results from a line with a standard
mould heater
FIGURE 2: Birefringence results from a line with an
improved system (see later text)
Dishing, which is the flatness of a disc, is influenced by the temperature within the mould cavity
(temperature is the result of injected polycarbonate combined with the coolant temperature).
The two types of Dishing are SKR – (Radial Deviation for DVD), which depends on the
temperature difference between mould halves, and is the flatness of discs in a radial direction.
SKT (Tangential Deviation for DVD) depends on the temperature of the mould and is flatness of
the disc in a tangential direction.
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High HF Signals and poor Jitter are caused by poor formation of pits and lands, and prevent
players from recognizing and decoding data. While these parameters are largely dependent on
stamper quality, they are also significantly influenced by moulding conditions.
Traditional mould temperature regulation techniques have been adapted from other industries
for use in the optical media industry. These techniques, which have slow start-up times, rely
simply on controlling temperature on what is often referred to as a constant flow cooling circuit;
these are no more than a simple thermal regulator in a pumped cooling system. The time taken
to adjust the temperature typically leads to significant disc rejects (often in excess of 100 discs)
before a new setting is stabilized. In the attempt to reduce cycle times, this temperature
adjustment becomes more difficult, and achieving a stable temperature more critical, thus
leading to more reject discs.
The problem ultimately leads to a compromise between the shortest cycle time and how many
discs one is prepared to sacrifice before this optimum performance is reached. This is
exacerbated when doing short runs with multiple stamper changes.
Another potential, but significant, failure of these traditional mould temperature regulators is that
the systems overall can lead to extremely contaminated coolant flowing through the mould. This
reduces mould life and can lead to catastrophic failure of the cooling system (typically pump
seal defect) following even modest shut down periods as part of routine maintenance.
These drawbacks point to an obvious need, first of all, for a temperature regulating system that
is designed specifically with the optical media manufacturing process in mind. Among the key
elements would be a quick start-up time; fast response time to temperature changes; small
footprint; and low maintenance requirements.
Against this background, DaTARIUS, in conjunction with a select group of partners, developed
a revolutionary method of optimizing the mould temperature regulation utilizing patented
technology. The latest generation of this technology is the MF DisCo (Multi-format Disc
Cooling). Through this technology, the mould temperature regulation can be easily optimized to
suit all types of mould and production lines (both replicated and blank media) from CD and CD-
R/RW through DVD and DVD+/-R/RW, and beyond to BD/HD DVD.
Cycle Time
Mould Locked Signal
on
MF DisCo “flow
off
Hold Time
Mould Close Signal
Injection start
Hold Pressure Start
Cooling Time
Mould Open Signal
Mould Fully Open
Eject and
Take Out
Time
FIGURE 3: The moulding cycle with MF DisCo
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Whereas the traditional approach to mould temperature regulation is through ‘constant flow’
cooling, it is clear that the moulding process of optical discs is itself is a cyclical process, and
the heat load to the steel in the mould is, therefore, a cyclical load. Accordingly, the basis
behind the MF Disco technology is a high-precision direct coupled temperature regulator that is
synchronized to the moulding process, utilizing a far smaller volume of coolant. Through this
synchronization the flow of coolant is adapted to each of the moulding process stages. This not
only allows optimization of the moulding process itself, but also allows a far more rapid
response time to any requested temperature change, through to a far faster recovery to stable
process following stamper change or any stoppage of the line.
In addition to quality issues, costs are a factor in media manufacturing not to be overlooked, and
with mould temperature regulation there are considerable potential savings in start-up,
temperature changes, and energy. After a stamper change, traditional mould temperature
regulation has taken at best 30 shots to achieve good discs; with MF DisCo, the number of
shots is reduced to as few as 3, providing an instant savings of 27 discs per stamper change.
After each stamper change, the temperature needs to be optimized to that particular stamper.
During this process, further reject discs can be produced while seeking the optimum
temperature. With the faster reaction times of MF DisCo, the quantity of rejected discs here can
also be greatly reduced, resulting in considerable cost savings per year.
A further saving with this direct coupled coolant approach is that up to 65% savings on energy
consumption can be made when compared with standard mould temperature regulators; in
addition, the MF DisCo is designed to replace two standard mould heaters, leading to further
cost savings per year.
Standard Mould Regulator
Mirror Temperature
Minimum temperature of
disc for ejection
MF DisCo
Mirror Temperature
*
FIGURE 4: * Cycle time reduction and wider process window for more stable quality in a line
using MF DisCo
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The special technology behind the MF DisCo has been proved for over five years, with the latest
generation MF DisCo on the market for two years. It has been installed in over 1,300 lines
worldwide, with significant cost savings and improvements in quality being reported by all the
replicators involved. The above figure demonstrates the improvements in the manufacturing
process window that are possible with an MF DisCo installed on a DVD replication line.
DaTARIUS Corporate Information
DaTARIUS is a world-leading supplier of test equipment, not just proving but also improving
optical media quality through comprehensive products and services embracing process
optimization. Our Analyzers and Evaluators support all formats: pre-recorded, recordable, and
rewritable, and our revolutionary DaTABANK technology is fully Blu-ray Disc (BD) and HD-DVD
enabled. Complementing these testers: optimization, including our MF DisCo temperature
regulator; and inspection, with print label, disc orientation and ident code validation. We also
offer extensive training through our service and test centres worldwide. For the past 18 years
DaTARIUS has been at the forefront of optical media technology with our commitment to the
future of the industry and our customers.
For more information on the company and its products, visit www.DaTARIUS.com
Copyright 2004, DaTARIUS All rights reserved. All other trademarks or registered trademarks are the property of their respective
owners.
DaTARIUS Group
The quality people – measurement, inspection, and process optimization solutions