Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2000-06-29
2003-11-04
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C428S457000, C430S270120
Reexamination Certificate
active
06641886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to the field of optical media. More particularly, the invention relates to time sensitive disposable optical media.
2. Discussion of the Related Art
Optical disks such as CDs and DVDs are sold and rented to consumers for use at home. The content of the optical disks may be music, movies, software or data. Unfortunately, the purchase of CDs and DVDs can be expensive. The cost is associated not primarily with the manufacturing cost of the optical disks, but with the value of the information, such as movies or software, encoded on the disks. Content providers, such as movie studios or software companies, do not want to sell at a low cost copies of their material that will have a long lifetime in the marketplace. Rentals of CDs and DVDs enable consumers to access the information at a lower cost, but the need to return the rentals on time is inconvenient. It would be desirable to have an optical media (e.g., disk) that the user could purchase at a low cost, would address the concerns of the content providers about lifetime of their content in the marketplace, and which would not have the disadvantage of having to be returned, as is the case with videotape movie rentals today. It would also be desirable to manufacture such an optical disk at low cost and with minimum changes to existing optical disk manufacturing processes.
CDs and DVDs are generally manufactured according to the following process. This information was downloaded from the web site of Disctronics Manufacturing (UK) Ltd., Southwater Business Park, Southwater, West Sussex, England on Jan. 26, 1999, and has been slightly edited.
3. CD Mastering
Mastering of CDs and CD-ROMs is a complex process needed to create a stamper (used to mould the CDs) from the premastered data. The processes are carried out in a class 1,000 clean room. Operators wear special clothing including face masks and footwear to minimize any particles.
4. Glass Master Preparation
Glass Master Preparation of the 240 cm diameter 6 mm thick glass master starts by stripping the old photo resist from its surface (since the glass blanks can be recycled). This is followed by cleaning and final washing using de-ionized water. The blank master is then dried carefully ready for the next stage.
The surface of the clean glass master is then coated with a primer and then a photo resist layer 140 to 150 microns thick by spin coating. The thickness should be matched to the molding cycle time. Shorter cycle times imply a thicker resist layer to ensure good pit geometry. The uniformity of the layer is measured with an infra red laser.
The photo resist coated glass master is then baked at about 80° C. for 30 minutes. This hardens the photo resist layer ready for exposing by laser light.
(a) Laser Beam Recording
A Laser Beam Recorder (LBR) is used to expose the photoresist layer on the glass master where the final pits are required.
This is carried out in a class 100 controlled environment using a high power gas laser directly from the premastered source audio or CD-ROM data. The laser can be blue, violet or (for DVD and CD mastering) ultra violet. The laser beam is modulated to expose the photoresist where pits should be while the glass master spins at exactly the correct linear velocity and is moved gradually and smoothly to maintain the correct track pitch and linear velocity.
The LBR is controlled by a PC based system which formats the data from the source CD, U-matic or Exabyte tape with the CIRC error protection and EFM modulation. If an error occurs which cannot be corrected during mastering the controller will abort recording.
Speed of laser beam recording depends on the machine and input media. At one time when every CD was audio, U-matic was the only media used and only allow single speed mastering. Other newer media allow faster mastering up to 4 times, with even faster speeds possible. The following table summarizes the mastering speeds for different media.
Media
Input
Speed
Comments
U-matic (1630)
1×
Still in use but is gradually being phased
out. Audio data is often transferred
offline to a faster format before mastering
DAT
1×
Not a preferred format for mastering
CD
4×
Faster if LBR capable
CD-R
4×
Depends on quality of CD-R media used
and speed of LBR
8 mm Exabyte 8500
2.8×
Max speed of Exabyte
8 mm Eliant 820
4×
Faster if LBR capable
Hard disk
4×
Faster if LBR capable
The absolute limit of speed is dictated by the robustness of the glass. For 240 mm glass plates, the practical limit is around 6× for CD mastering.
Network mastering is a new development whereby the data content of Exabytes, CDs etc (containing the audio or other data) is transferred to a server and mastering carried out from this data (which can be checked prior to mastering) via a high speed network. Several LBRs can be connected to the network and mastering jobs can be scheduled in advance. The result is higher speed, more reliable mastering.
(b) Development & Metallization
The exposed photoresist surface is developed to remove the photoresist exposed by the laser and therefore create pits in the surface. These pits should extend right through the photoresist to the glass underneath to achieve good pit geometries as specified in the Red Book. The glass itself is unaffected by this process and acts merely as a carrier for the photoresist.
The active surface (i.e. containing pits) of the developed glass master is then metallized either with nickel or nickel alloy created by sputtering or with silver by evaporation. If nickel or nickel alloy is used this becomes part of the Father which is created by electroforming so the pit geometry is maintained. If silver is used, the nickel Father is grown on top of the silver resulting in some distortion of the pit shapes, but this is not usually enough seriously to impair the resultant pits.
(c) Electroforming
This involves creating nickel fathers, mothers and stampers by electroforming in a class 1000 clean room environment.
The father is electroformed from the metallized glass master and then the surface containing the ‘bumps’ is oxidized ready for the next stage. (This allows the mother to be separated from the father).
The mother is then electroformed from the father and is an essential intermediate stage from which the stamper(s) are then electroformed in a similar way.
After the mother has been created, the father can then be used as a stamper. Only mothers are needed for subsequent stampers. Additional stampers are created for long runs of CDs.
The photoresist on the glass master is then removed and the glass cleaned ready to be used again. If silver is used, it is recovered and recycled.
(d) Stamper Finishing
When the stamper has been electroformed from the mother, it requires finishing before any discs can be replicated from it.
Each stamper is checked visually, the back polished, it is punched to the required outside diameter, a hole accurately punched in the center and finally it is checked on a stamper player before being fitted to the press.
Stamper finishing is an important stage as it will affect the quality of the final disc. The center hole must be accurately cut to avoid eccentricity which could affect the playability of CD-ROMs using modem high speed CD-ROM drives. Also the stamper thickness must be uniform to avoid unbalance problems in the finished discs.
Finished stampers are stored in protective plastic packages ready to be fitted to a molding machine.
5. CD Replication & Printing
CD Replication Overview
Compact Discs, whether audio or CD-ROM, are manufactured in the same way using the following processes:
Injection molding of the clear polycarbonate discs using a hydraulic press.
Metalising to create an aluminum reflective surface
Lacquering to protect the back of the reflective surface
Printing of the disc label on top of the lacquer.
(a) Replication Lines
The replication of CDs in the past has been carried out using batch processes where each stage of the process uses a different machine. In t
Bakos Yannis
Brynjolfsson Erik
Flexplay Technologies, Inc.
Hale and Dorr LLP
Mulvaney Elizabeth
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