Quantcast How are retail DVDs created? - digitalFAQ Forum
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11-05-2009, 10:31 AM
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There is much discussion about the factors that differentiate brands of recordable disc, but how exactly do the major home video studios create pressed DVDs? How does the science work and how does it differ from the creation of DVD-Rs?
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11-05-2009, 12:33 PM
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Retail DVDs are replicated with pressing equipment.
  • NOTE: When you copy to burn discs, it's called duplication. You duplicate using burned media, and replicate using pressed media.
A glass master (or stamper) is laser-etched from the data on your submitted DLT or DVD-R (Authoring or General) -- some can even take DVD+R, RW, RAM, ISO on hard drive, etc. Using the master, the polycarbonate/plastic platter is pressed into the correct shape, and topped with a reflective foil. This glass master is expensive, and is why a 500-disc run often costs nearly the same as a 1,000-disc run. The bulk of your funds is spent on the mastering, and the discs themselves are worth mere pennies.
  • NOTE: Remember that computers understand binary. Sometimes referred to as 1's and 0's, or even simply "on" and "off".
The pressed disc physically has pits (indents) and lands (flat surface), which pass different amounts of light. When the laser drops off into the pit, it is "off". When the laser reflects from the land, it is "on". (Or vice versa, I forget which is the 1 and which is the 0 -- really doesn't matter for this conversation.)
  • NOTE: Some people are inclined to pick up a disc and look, expecting to see a "Swiss cheese" surface. After seeing nothing, however, they quickly claim they "don't see anything" and can't understand. Remember that these are measured in mere nanometers, microscopic in size.
A burned disc uses a laser to physically burn a microscopic dark spot, to mimic a pit. The unburned surface mimics the land.

Pits and lands are read within the groove, or spiral "road" that the laser reads from, as the disc is spun at high speeds. When a burn writes outside of the groove (or even when a press does not fall within the groove), you get bad discs, because the data cannot be read. DVDs can't offroad!

On really crappy DVD recordable media, using a magnifying glass, you can sometimes see mottling of the disc surface, on a burn. The burned pits are not precise, but rather fades across a larger area outside the groove. I've added a photo of one several posts down.

Remember that the disc is spinning, and to stay inside the groove, the disc needs to stay as flat as possible, and not wobble. There is some built-in tolerance for how much wobble is allowed, both in burning and reading. The data is not written in a straight line, it wiggles a bit. As long as the laser can pick-up data within the groove, it's fine -- even if the burned data appears to be burned by a drunken laser! Beyond this, remember your physics! The outer edge of the disc is spinning faster than the interior. It's also wobbling more. This is why so many cheap discs "coaster" towards the end of a disc, especially in that last 400-500MB worth of space.

The dyes used in write-once discs, and phase-change crystalline metals used in re-recordable/rewritable discs, reflect light using a combination of the material itself, and the foil above it. While the light does reflect, it is not as reflective as the pressed discs. Some dyes, such as the metallic AZO dyes used by Mitsubishi, use a metallic base that assists in the quality of reflection -- one of the reasons their discs are so well-liked and perform so great. Cheap dyes with many imperfections, on the other hand, impede light reflection too much, resulting in the many read errors. Ritek's organic dye is infamous for poor readability, as seen from various tests and reviews online, both by research bodies and home amateurs.

Dual-layer pressed media is essentially two platters on top of one another, with a semi-transparent spacer between them. The extra layer does not really affect disc reflectivity.

Double-layer recordable media
is a bit more complicated, because there are multiple write surfaces, with various levels of translucence and transparency. I don't really want to explain that if I don't have to, can be hard to explain using regular English. SuperMediaStore has a write-up, but it's still fairly wordy and techie. Disc reflectivity can tank pretty badly on recordable dual-layer/double-layer media, especially when the materials are substandard quality.

Double-layer recording is also complicated further due to the inconsistency in construction among manufacturers, and compatibility among burners. By this, I refer to inverse stack process vs 2P process. Most all burners are fine with the original 2P discs, but the inverse stack discs will either burn poorly or fail to burn at all in a large number of burners out there in use. However, inverse stack is cheaper to produce. Further complicating this already complicated issue is the fact that the cheap production method is being used by the typical low-quality and mediocre-quality blank disc manufacturers, so you have discs with multiple possible problems!
  • Poor reflectivity (imperfect dyes and materials)
  • Poor materials (dyes, polycarbonates, foils, glues, etc)
  • Poor quality control (QC), quantity over quality
  • Lowered compatibility of IS vs 2P
It's no mystery why so many people have troubles burning DVD+R DL, even more than the people using cheap/generic single-layer DVD-R/etc!

As you're probably understanding now, burned media are quite a different critter from your basic pressed disc.

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11-05-2009, 12:34 PM
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OSTA has a decent write-up that isn't too complex, with more information on non-pressed disc construction.
From http://www.osta.org/technology/dvdqa/dvdqa13.htm

Quote:
Originally Posted by http://www.osta.org/technology/dvdqa/dvdqa13.htm

What is the construction of DVD-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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11-05-2009, 12:41 PM
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The British duplication/replication service WizBit has a decent write-up on the glass mastering process.
From http://www.wizbit.net/cd-dvd_product...ass_master.htm

Quote:
Originally Posted by http://www.wizbit.net

A glass master, also referred to as a 'stamper' is used to punch all of the data pits into a CD or DVD during the process of replication.

The reason why it is called a glass master is because the information is copied onto a special chemical coating on a circular block of glass. The block of glass is actually much larger than a CD (they are typically 240mm in diameter and 6mm deep) to facilitate handling and to avoid the sensitive data area from being touched or damaged.

The glass master is polished until it is ultra smooth as even microscopic scratches can affect the quality of the CDs being produced.

Glass mastering is performed in a Class 100 clean room (10 times cleaner than an operating theatre). A Class 100 cleanroom is designed to never allow more than 100 particles (0.5 microns or larger) per cubic foot of air (typical office building air contains from 500,000 to 1,000,000 particles per cubic foot of air). This is because dust, pollen and smoke particles can all affect the quality of a CD glass master whilst it is being prepared, so the mastering facilities are kept as clean as possible.

There are three principle steps involved in creating a glass master:

Step 1 - Photoresist mastering and Laser Beam Recording (LBR)

The first step in producing the glass master is to clean the glass plate with detergents and to then apply a photoresistive light-sensitive material of about 140 to 150 microns that is then burnt using a Laser Beam Recorder (LBR) which is a deep blue or ultraviolet laser. When exposed to the laser light, the photoresist undergoes a chemical reaction which hardens it.

After mastering, the glass master is baked at about 80C for 30 minutes to harden the developed surface material and prepare it for metalisation. Metalisation is a critical step prior to electroplating with nickel.

Step 2 - Metalisation of the glass master

After the photoresist mastering, the developed glass master is placed in a vapour deposition metaliser which lowers the pressure inside a chamber to an extreme vacuum. A piece of nickel wire is then heated to white hot temperature and the nickel vapour is deposited onto the rotating glass master. The glass master is coated with the nickel vapour up to a typical thickness of around 400nm before being removed.

Step 3 - Electroforming

The information contained on the metalised glass master is extremely fragile and it must be transferred to a more resilient form for use in the injection moulding equipment.

The metalised master is therefore rotated in a plating tank containing a nickel salt solution (Nickel Sulfamate). The electroforming process takes approximately 1 hour to create a 0.3mm thick uniform nickel layer.

This master is then called the 'father' and a negative of the father, the 'mother' needs to be created to be able to punch the pits and grooves into the membranes on the final CDs or DVDs that the customer will receive.

The mother glass master is created from the father using electroforming and the mothers are then used to punch holes in the membrane layer on replicated CDs or DVDs that will then allow light through to reflect off the silver aluminium layer above the membrane layer in the centre of a CD or DVD.

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11-05-2009, 01:07 PM
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If you're still in a reading mood, the respected optical disc testing firm DaTARIUS released a really good paper on dual-layer/double-layer recording. See the attached PDF.

However, I would like to point out this incorrect statement:
Quote:
16 hours of VHS quality video.
"VHS quality" is NOT 352x240. That's VCD quality, below that of VHS. I really wish people would quit confusing x240 pixels with "240 lines" of a VHS tape -- it's not at all the same, they measure different dimensions (one vertical, the other horizontal). It requires 352x480 to truly re-create "VHS quality" on a DVD. And the most you can squeeze on a dual-layer DVD is about 5.5 hours, without losing your bitrate allocation (thereby creating block artifacts). Some content allows for more compression -- cartoons, for example -- up to about 7 hours on a disc. That's still a far, far distance from the quoted "16 hours" figure. Youtube video would look better than a 16-hour DVD.

Anyway, good read, VHS statement aside!

.


Attached Files
File Type: pdf DoubleLayer-Datarius.pdf (222.7 KB, 0 downloads)

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11-05-2009, 01:20 PM
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And risking overkill, here's some more! Check out these videos:

"Reload page to view video."


Also
http://www.youtube.com/watch?v=ncU_A76W3P8
http://www.youtube.com/watch?v=XWGBa05-qz4
http://www.youtube.com/watch?v=Qqlgtvwjml4

Whew!

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11-06-2009, 10:29 PM
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Here's a photo of a disc with mottled and splotchy dye:

baddyephoto.jpg

If you look closely, you can also see some zonal burning rings. The faster the burn got, the worse the dye reacted.
This photo doesn't really show the full effect, it's covered in speckles.

There was also a bad spot easily visible in the dye, near the outer edge:

You must be logged in to view this content; either login or register for the forum. The attached screen shots, before/after images, photos and graphics are created/posted for the benefit of site members. And you are invited to join our digital media community.


If you darken and filter it, you can see the problem goes deeper than is easily seen by the naked eye:

burnspotphoto.jpg

The burn is crap -- a coaster.



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  #8  
11-07-2009, 01:18 AM
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Holy crap, thanks Admin! Now to find the time to go through all that
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