DISC CONSTRUCTION AND MANUFACTURING

What is the construction ofDVD-R and DVD+R discs?
DVD-R and DVD+R discs can be either single or double-sided. A single-sided (SS) disc is composed of a recording side and a dummy side while a double-sided (DS) disc consists of two recording sides. The recording side of a DVD-R and DVD+R disc is a sandwich of a number of layers. First comes a polycarbonate plastic substrate containing a shallow spiral groove extending from the inside to the outside diameter of the disc. A DVD-R disc additionally includes pits and lands on the areas between the coils of the groove (land pre-pits). Added to this substrate is an organic dye recording layer (azo, cyanine, dipyrromethene or others) followed by a metal reflective layer (silver, silver alloy, gold). The dummy side of a single-sided disc consists of an additional flat polycarbonate plastic substrate (sometimes with an additional metal layer to obscure the bonding layer from view for aesthetic purposes). An adhesive then bonds two recording sides (for a double-sided) or a recording and dummy side (for a single-sided) together into the final disc. Some single-sided discs are also topped on the dummy side with decorations or additional layers that provide surfaces suitable for labeling by inkjet, thermal transfer or re-transfer printers.

How are DVD-R and DVD+R discs made?
The first step in manufacturing a DVD-R or DVD+R disc is to fabricate the polycarbonate plastic substrates (incorporating the spiral groove and land pre-pits) using an injection molding process. The dye is then applied using spin coating and the metal layers by means of DC sputtering. After both sides of the disc are completed they are bonded together using a hot melt, UV cationic or free radical process. Additional decoration or printable layers are typically applied using screen printing methods. A DVD-R (General) disc undergoes a further manufacturing step in which a specialized computer DVD recorder is used to “prewrite” information in the Control Data Zone of its Lead-in Area to inhibit direct copying of prerecorded DVD-Video discs encrypted with the Content Scrambling System (CSS). Apart from this, and some minor differences in the configuration of the molding stamper used to create the substrates, the process for manufacturing DVD-R and DVD+R discs is virtually identical.

What is the construction of DVD-RW, DVD+RW and DVD-RAM discs?
To allow information to not only be written but also re-written many times over, DVD-RW, DVD+RW and DVD-RAM (rewritable) disc construction is more complex than that of DVD-R and DVD+R (recordable). Just like a recordable disc, a rewritable disc can be either single or double-sided. The recording side of a rewritable disc also uses multiple layers beginning with a polycarbonate plastic substrate containing a shallow spiral groove extending from the inside to the outside diameter of the disc. A DVD-RW disc additionally includes pits and lands on the areas between the coils of the groove (land pre-pits) and a DVD-RAM disc also inside the groove itself (land and groove). Next comes a dielectric layer (zinc sulfide and silicon dioxide), followed by a phase-change alloy recording layer (either indium, silver, tellurium and antimony or germanium, tellurium and antimony), another dielectric layer and a metal reflective layer (silver, silver alloy, aluminum). Additional layers may also be incorporated above or below the dielectric layers (germanium nitride, silicon carbide, silicon dioxide, silicon nitride, zinc sulfide, antimony telluride and others). The dummy side consists of a flat polycarbonate plastic substrate sometimes with an additional metal layer. An adhesive then bonds the sides together into a single disc. The exterior of the recording side may also be “hard coated” with a transparent material (indium tin oxide, silicon-based lacquer and others) designed to repel dust and resist fingerprints and scratches. Similar to a barcode in appearance, a DVD-RAM or DVD-RW disc can also contain near its inner diameter an optional Burst Cutting Area (BCA) or Narrow Burst Cutting Area (NBCA) to supply information required to implement Content Protection for Recordable Media (CPRM).

How are DVD-RW, DVD+RW and DVD-RAM discs made?
As with DVD-R and DVD+R, producing DVD-RW, DVD+RW or DVD-RAM discs involves using multiple manufacturing stages. The first step is to fabricate the substrates (incorporating the spiral groove, land pre-pits and embossed areas) by injection molding. The dielectric layers, phase-change recording, reflective and any additional layers are applied to the substrate using DC, RF and reactive sputtering. After both sides of the disc are completed they are bonded together using a hot melt, UV cationic or free radical process. Since the sputtering process lays down the phase-change alloy in its amorphous condition a special device using powerful lasers (initializer) returns the recording layer back to its crystalline state. Subsequent recording then results in less reflective (dark) areas being written against a more reflective (bright) background. The Burst Cutting Area (BCA) or Narrow Burst Cutting Area (NBCA) is marked into the disc using the initializer or a dedicated device outfitted with a YAG (yttrium aluminum garnet) laser. Hard coating can be applied to the substrates at different stages in disc manufacturing using a variety of processes such as spin coating, vacuum deposition and screen printing. A DVD-RAM disc can optionally undergo a further manufacturing step in which it is physically formatted by a conventional computer recorder (to detect and map any defective sectors). Apart from some minor differences in the configuration of the molding stamper used to create the substrates the process for manufacturing DVD-RW and DVD+RW discs is virtually identical while DVD-RAM fabrication is more involved.

How does writable DVD and CD disc manufacturing differ?
Apart from the thinner substrates and tighter manufacturing tolerances, the most significant difference between writable DVD and CD manufacturing is the need to perfectly bond two DVD halves together to create a disc that is the same thickness as a CD (1.2 mm). It is imperative that the two disc halves have the same long-term mechanical behavior to ensure that the resulting disc maintains its thermo-mechanical stability. This is particularly important for high-speed discs where flatness and uniformity are paramount. Writable DVD disc manufacturing equipment and production steps (with the addition of the bonding stage) closely resemble those used to fabricate their CD counterparts. In fact, many media manufacturers have simply modified their existing CD-R and CD-RW equipment to produce writable DVD discs although it is generally expected to become less feasible to do so (for productivity and product quality demands) as the technology and business evolves.

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