Article written by John Zois (DVD Bits Editor) on 29-Oct-2000
Photography and design by Tully Rosen

PREMASTERING AND GLASS MASTERING ROOMS

Here, the DLT is used to read the source data that will be used to ‘cut’ a glass master. The reason why they call it ‘glass’ master is because the information is copied onto a special chemical coating found on a circular block of glass. The pre-mastering room is also where the CSS key (encyption system to copy protect disc content) stored on a standard floppy disc is copied along with the DLT data onto the master. The encryption key itself is encrypted so that in the event of falling in the wrong hands it cannot be used to extract the data stored on DVDs.

The actual cutting of the glass master is done in a room next door to the pre-mastering room, by a special gas laser called the Laser Beam Recorder (LBR). The LBR encodes the information by forming pits on the substrate on the glass plate, which is then developed (like a photographic film would but in a very different way) exposing the area that has been cut.

The laser itself costs $125,000 every 2 months to operate. The room where the cutting is done is located on top of a 6 foot concrete slab with the laser cutting equipment placed on a thick block of granite. These measures are to ensure that zero vibration is present during the cutting which would affect the formation of an accurate glass master.

  Once the image has been created on the substrate on the glass master, the entire glass block is taken into a special room containing $15 million of equipment and has a class 10 environment (10x cleaner than any surgery). There is special lighting used in this room so as not to affect the photo resist on the glass master. Unfortunately the strict lighting restrictions prohibited us from photographing this room.

De-ionised water is first used to clean debris off the plate before proceeding. The solution turns the exposed areas into base soluble salts, then water rinses it away leaving the image A laser is then used to to determine when the pits are formed and to "switch off" the development solution. The solution turns the exposed areas into base soluble salts and then water rinses it away leaving the image. A robot arm then carries the glass master into  a vacuum chamber (-5 bar of vacuum pressure) where it will be coated in nickel thus making it conductive for electro-plating, the next step in the process.

As you can see the first stage in the manufacturing process is quite complex and is probably the most important step as even small imperfections will have detrimental effects later down the line. Therefore the first stage doesn’t come cheap, with PMI charging about $2,000 for just creating the glass master alone.

ELECTROFORMING ROOM

Once the process of creating the glass master has been completed, the master is brought into the electroforming room and placed into an electrolytic cell in order to create a nickel master. The nickel master will be then used to ‘replicate’ thousands of copies of the DVD in the replicating machines.

Pure nickel in the form of hundreds of solid beads is added to the electrolytic cell and it slowly dissolves into the electrolyte. The nickel will coat the entire surface that was made electroconductive in the glass mastering room, with the entire electrolytic process taking about an hour. Debris are then washed off in a bath containing special cleaning agents that are not abrasive to the nickel master.

  The nickel plated onto the surface of the glass master is then removed to create a negative image, which will serve as the master for ‘printing’ the DVDs. The nickel master though has an outer diameter which is just excess nickel and is thus punched out and re-used. After processing, the glass plate which is worth ~$2000 is cleaned and reused time after time thus saving precious resources.

Each nickel master produced by PMI and used to print each DVD title is catalogued and linked to orders, ready to be mass-produced at a moment’s notice by the studios when retail stocks become exhausted. There are usually about 20,000 masters in this room at any one time (DVDs, DVD ROMs, CDs and CD ROMs), a staggering fact to contemplate.

While to manufacture a DVD you need to create a glass master and then a nickel master, PMI only does this for the Australian authoring house DVM who in turn authors DVDs for the Australian based studios (Roadshow, Magna Pacific etc). International studio distributed products such as Columbia Tristar, Warner Brothers, 20th Century Fox etc have their glass masters made in the USA so PMI uses those to perform the rest of the manufacturing process, from the nickel master manufacturing stage and onwards.