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How are DVDs Made for use in Copiers???

As CD/DVD copiers are becoming more available to the community and as time progresses, having a CD/DVD copier in your business will be a common place occurrence. With copiers, a business can now take control of their own production goals and schedules and produce finished product that rivals any replicated media.

DVD (Digital Versatile Disc) quickly emerged as the next step in optical disc technology. DVD-Video has established itself as the format for delivering high-quality digital video. It’s also evolved into a complete software storage and distribution solution for enhanced computer applications. DVD-Video and DVD-ROM, the first DVDs to hit the consumer market, are pre-recorded versions that are ideal for full-length feature films and computer games with highly advanced graphics.

When CD-ROM was developed most people never imagined that they would require anything beyond its 650MB capacity. The digital revolution has pushed the compact disc technology to its limit. Developers and content owners began to realize the need for a medium capable of processing today’s advanced applications.

In September of 1995, two major groups (Sony/Philips and Toshiba/Time Warner), each developing their own format, agreed to a single standard for a high-density optical disc, a “best practices approach.” Sony/Philips’ stressed the importance of EFM+ modulation and backward compatibility with the CD format; DVD desktop machines play Audio CDs and DVD-ROM drives play most CD formats. The standard also adopted Toshiba/Time Warner’s format of bonding two 0.6mm substrates for a double-sided disc with 1-4 data layers.

A DVD is analogous to a quad-density compact disc because it has approximately 4 times as many pits as a CD in the same size area. In the mastering process the laser creates smaller pits along a tighter spiral.

The result is an optical disc that can hold up to 26 times the data of a CD. DVDs can store from 4.7GB (single-sided, single layer) to 17.0GB (double sided, dual layer) with up to 133 minutes of full motion MPEG-2 video on each layer. With its superior audio and video quality, increased data capacity, interactive potential and Internet compatibility, DVD is a medium for the next millennium.

DVD Formats:

DVD-5 (single side, single layer) DVD-9 (single side, dual layer) DVD-10 (double side, single layer) DVD-14 (DVD-5 single-layer bonded to a DVD-9 dual-layer) DVD-18 (two bonded DVD-9 dual-layer substrates)

(Note: all discs are the standard 1.2mm thickness)

DVDs are similar in nature to CDs. Data is recorded in a spiral track of pits, and the 4.75-inch diameter-discs are both read with a laser beam. As with CD manufacturing, there are five production stages: Mastering, Electroforming, Replication, Printing and Packaging. But key manufacturing and internal design differences make DVD a superior product.

DVD-Video requires extensive post-production work at a “Compression and Authoring House” before the assets are delivered to the replication facility. After a movie has been transferred from film to videotape, it must be specifically formatted for DVD. Technicians scan the tape for screen changes, insert pan-and-scan codes, and enter closed-caption information.

Since digital video has numerous elements that are the same, most of the data that represents the video can be removed through encoding. The video is compressed into the MPEG-2 format using variable bit rate encoding. After the audio is compressed into the Dolby AC3 Surround Sound format, the compressed audio and video are merged to create a single data stream. Then the data assets are manipulated on powerful PC workstations with DVD authoring software in order to create a DLT (digital linear tape) from the various data and compressed video/audio.

The DLT is sent directly to the manufacturing facility. It is a well-established SCSI tape medium, which has become the de facto mastering standard. DLT is a robust format with data capacity of up to 20.0GB - slightly larger than 8mm tapes, but smaller than VHS tapes.

Before the DLT is sent to mastering, a Premastered Media Format Verification (PMFV) is performed. The DDP (disc description protocol), essentially the table of contents, is checked to confirm security scrambling status, regional coding, video title sets and end sector necessaries. It is also at this point that the copy protection (MacrovisionTM and/or Content Scramble System) is reviewed and verified. The customer supplied DLT is now ready for mastering.

DVD-ROM requires an entirely different premastering setup. The customer’s data can be submitted on various input medium types, including hard drives, tape backups, multiple CD-Rs, DVD-Rs, etc. The data is collected, merged and placed in a single environment per the customer’s expectations and directory structure guidelines.

The image creation process begins and the content is formatted according to the customer’s request, options include Micro UDF (Universal Disc Format – compatible with ISO 9660), strict ISO (for DOS), Joliet naming, file placement, transition and layer breakage (only for DVD-9, certain files on a certain layer), etc. The formatted content is output to a DLT in DDP 2.0 specification, and then it’s ready for mastering. Micro UDF was initially combined with ISO 9660, today’s PC standard. UDF is now the standard DVD file format and has already begun to extend and modify what is currently possible with ISO.

The rest of the manufacturing process is the same for DVD-Video and ROM. Before accessing the content on the DLT, we begin with the preparation of 240mm (9.5 inch), 6mm thick glass master. It’s chemically cleaned with nitric acid and solvents and washed using de-ionized water. After it’s carefully dried, the clean glass master is coated with photo resist (a light sensitive chemical) 130 nanometers thick. The coated glass master is baked for 20 minutes to remove the carrier solvent.

Using a binary code, a computer translates the data from the DLT in a series of “on and off pulses” (pits and lands). A Laser Beam Recorder (LBR) exposes the photo resist with each “on pulse” from the laser. The UV laser has a finer focus (than the blue laser) and burns a smaller writing “spot,” which is necessary for the shorter, narrower DVD pits. The laser records onto the glass in a spiral track from the center to the outside.

Cutting a full 4.7 GB single layer DVD takes over 90 minutes. This time will decrease with advances in encoding. A complete DVD could contain up to four mastered layers; each layer requires it’s own mastering cut. A DVD project is more expensive to manufacture than CDs, but the benefits are tremendous.

After recording, the glass master is developed with an alkaline. The photoresist is washed away at each exposed “on pulse” creating a tiny pit of information on the surface of the glass master. The glass master is then placed into a vacuum chamber and the surface is covered with a small amount of nickel. This process, sputtering, produces a metalized glass that conducts electricity during the next stage, electroforming. Compact discs are sometimes coated with silver, but nickel encourages a cleaner pit definition, which is important for DVD manufacturing.

Electroforming begins when the metalized glass master is placed into a bath of Nickel Sulphamate solution. An electric current is sent through the bath and the positively charged Nickel ions in the solution give up their charge at the surface of the glass master, which acts as the cathode. Nickel balls are placed at the anode which corrode from Nickel atoms into Nickel ions replenishing the solution. Subsequently, a layer of Nickel grows on the surface of the glass. When the glass is removed from the tank, the Nickel is separated from the glass. This sheet of Nickel, a reverse image of the data, is called the father or metal master.

Because DVDs have smaller pits and require a reading laser with a finer focus, they require optimum pit replication. Nickel sputtering produces a high-resolution image of the photoresist layer. The closer you can emulate the glass master, the more accurate the final product is likely to be. The de-silvering procedure (removing the thin evaporated layer of silver from the nickel father) can change the pit volume.

After the metal master has been separated from the glass, it is actually possible to use it for replicating discs. Instead the father is put back into the Nickel Sulphamate and two successive layers are grown. First the mother (a positive data image), and then the stamper, which is grown directly from the mother. The stamper has negative pit impressions just like the father. After punching out the center hole and outer edge and polishing its backside, the stamper is ready to be loaded into an injection-molding machine. The father and mother are saved to grow more stampers for future replication runs, thus saving the manufacturer production time.

The stamper is then loaded into an injection-molding machine for disc replication (literally making a replica of the image on the stamper). Two machines are required to make one DVD and each mold produces a 0.6mm disc. Polycarbonate is heated to a molten state and fed into the mold, which contains the stamper. Under several tons of pressure the plastic is compressed against the stamper and the pits are pressed into the plastic. The clear plastic disc, with the data intact, is chilled and removed from the mold.

“Molding a DVD disc” takes approximately 5 seconds. After they are pressed, one or both (depending on the format) 0.6mm substrates are sputtered with an aluminum or gold layer, and then they’re bonded with lacquer and UV light (it is important to note that the bonding process will differ extensively for both DVD-14 and DVD-18). A DVD-5 only has content on one side; the other half is a dummy substrate. The content side must be aluminized, but commonly both sides are sputtered (if pit-art is used for customer artwork, then the second layer must be aluminized, too). Since a DVD-10 has content on both sides, both substrates are sputtered with aluminum before bonding.

DVD-9 includes a dual-layer feature, which allows both data layers to be accessed from one side. The bottom substrate is coated with a semi-reflective gold layer, while the top half gets aluminum. This allows the laser to read content from the bottom substrate (layer 0) and when necessary refocus and read through the gold layer in order to get data from the second layer (layer 1).

After sputtering the substrates, they are ready to be bonded. A lacquer coating is applied to the top of one side and it is spun evenly via centrifugal force. The lacquer acts as a bonding agent as the discs are squeezed together and placed under a UV light. The UV light cures, hardens and seals the bond. The bonding adds an additional step (over CD) to the manufacturing process. Applying the lacquer coating has been integrated in-line with the injection-molding machines and is usually used for all DVD formats.

Both standard magazine-quality offset and silkscreen printing are available for DVD. The different formats have their own disparate printing options. In addition to offset and silkscreen, DVD-5 also offers pit-art (laser graphics) in lieu of data on the dummy substrate. The customer’s artwork is printed on photographic paper as a template, which is used on mastering lathes to make a pit-art master stamper. The image is transferred to a stamper and the molded clear disc contains the pit-art image. It is the most cost-effective DVD decoration and identification technique. The graphic image is a long series of “off pulses” that defract light to create the customer’s design.

Since a DVD-10 must be flipped to read data from each side, printing is only available within the inner band, a 4mm area around the center of the disc. DVD-9 silkscreen printing options are reduced by the adverse effect of the UV light on disc flatness. The UV light dries the ink; certain inks harden to a point where it will slightly bend the disc. Because of the tighter spec, DVDs must be mechanically and physically more precise than CDs. This is especially true for DVD-9 with its semi-reflective layer. Offset printing is a perfectly viable option for DVD-9 artwork. DVD-14 and DVD-18 will probably be limited to the same inner band option as DVD-10.

The disc flatness or “tilt” becomes the biggest production challenge. The disc thickness must be more uniform with reduced eccentricity from the outside track to the center hole. An integrated bonding technology during replication became crucial to producing the flattest possible discs. The disc itself is a more critical component due to the tighter pit focus (reduced jitter). Mechanical parity between the pre-bonded half discs is a necessity. All of this leads to an expanded step for DVD production – more extensive quality control.

Throughout the manufacturing process several different quality assurance tests are performed. The basic tests include a Data Verification System (DVS) test and signal verification tests. DVS ensures that the finished product is identical to the original image through a bit-for-bit comparison between the customer’s input data and the replicated disc. Signal verification tests confirm that the disc playback parameters are within required DVD specifications.

Environmental tests, including a storage test and a heat cycle test, ensure that DVDs remain playable and exhibit the same longevity as CDs. In addition, there is also an in-line test for flatness and a Differential Phase Detection (DPD) tracking test. DVD-9 has its own space-layer, semi-reflective layer testing. It is also important to check the disc in different manufacturer’s DVD players to confirm hardware compatibility.

After this extensive testing, the disc is ready to be packaged and shipped. Packaging has been entirely driven by market and content providers. The VSDA recommended that DVD-Video adopt a package similar in size to the VHS box, therefore retailers wouldn’t have to change their shelving configurations. The most widely accepted options are the Amaray Box, the AlphaPakTM and the SuperJewel Box. For DVD-ROM, the standard jewel-box is a cost effective and durable solution; various other options are also available. Nevertheless, it is important that the package is robust and protects the disc from damage during shipping. Now, the DVD is indeed ready to ship


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