How a CD (or DVD) is Made
There are two ways of making multiple copies of a CD. They are called Duplication and Replication.
This article deals with Replication. Our Duplication Service is described in a separate article.
The Replication process creates the discs out of the basic raw materials, polycarbonate; aluminium and lacquer.
The entire content of each disc is created simultaneously by injection moulding. This is also referred to as pressing.
The Compact Disc was developed as a way of distributing music but it is now used for a wide range of other media including Video, Data and Software. Whatever the use, we refer to the material on the CD or DVD as 'content' or 'data'. Before the data can be replicated it must be tested fully since it cannot be modified afterwards. It is also important that the original master copy which you supply is written in accordance with the specifications defined for CD's.
Once you have created and tested your master. You send it to us and the process can begin.
The first stage is to make the glass master.
The Glass Master
The Purpose of the Glass Master is to convert the data (music, video, software etc) from the digital information stored on your tapes, hard discs or CD-R/DVD-R to a mechanical representation of that data which can be used in the injection moulding process.
A glass disc with a very flat smooth surface is prepared by applying a layer of photographic emulsion to the surface. This layer has to be extremely consistent in thickness. Once the emulsion layer has dried, the glass plate is spun slowly round whilst a laser beam exposes the emulsion layer. The laser turns on and off as the binary digits 0 or 1, which comprise your data, are read from your original tape or disc. This 'cuts' an image, representing the stream of binary digits, in a spiral from the inside of the disc towards the outer edge. After this, the glass plate is 'developed'. Wherever the photographic emulsion has been exposed to the laser beam, the emulsion is removed. Where the emulsion has not been exposed, the development process has no effect. The result is that the data recorded as 0's and 1's on your original tape or disc, has now been turned into a spiral track of microscopic 'pits' created in the photographic emulsion layer.
A thin layer of silver is then evaporated onto the surface of the disc. This covers the surface of the plate and all the sides and the bottom of the 'pits'.
The Metal Stamper
Next we have to make a stamper. This is a nickel plate which is used as the mould on an injection moulding machine. The name comes from the era of vinyl records where the track groove was 'stamped' or 'pressed' into the plastic of the record.
The stamper is made by chemically plating a thin layer of nickel on to the glass master. The stamper is then separated from the glass master and cleaned. The surface of the nickel has 'bumps' where the glass master had 'pits'.
Replication is carried out in a sequence of events which are all managed on a single complex machine. First, the stamper is mounted onto the moulding tool. This operation calls for great care and cleanliness so that particles of dirt/dust do not get onto the surfaces of the mould or the stamper. The mould is closed and molten plastic is injected into it. The plastic flows in, over and around the 'bumps' on the stamper so that all the bumps make a 'pit' in the plastic. The plastic is cooled - the mould opens - the centre hole is cut and the disc is ejected onto the robotic handling mechanism which transports it to the next stage.
The moulded CD is placed into a chamber where vaporised aluminium is 'sputtered' on to the disc; creating a layer of aluminium on the pitted surface. This creates the mirror which reflects the laser beam which will read the finished disc when it is played.
The metalised disc is then sealed with lacquer which protects the aluminium from the atmosphere. A measured amount of lacquer is placed around the centre of the disc. The disc is then spun, so that the lacquer spreads evenly over the surface by centrifugal force. The lacquered disc then passes under an ultra violet light which cures the lacquer, resulting in a hard dry surface.
The playing surface of the disc is then scanned with a laser beam which can detect any faults which may be present and which could affect playability.
The discs are now brought together 'kitted' with the packaging items you specified. This may be a CD jewel case with a booklet and an inlay card or some other form of packaging; then everything goes to the packing department to be packed.
Packing may be handled by machines, or by hand, depending on the complexity of the job.
The finished discs are then dispatched by courier and finally, the end user will play the discs in a CD/DVD player or on a computer.