Compact discs or CDs are currently manufactured in a relatively complex process in which the information on the CD is first obtained for instance from a digital tape which is used to form a premastering disc that provides the information in a spiral pattern in a photo lithographic process. From the premastering disc, a master stamping disc is formed which is utilized in hot stamping a thermo plastic disc with grooves or interstices which carry the information from the premastering disc. The master stamping disc is made in an electroplating process followed by the utilization of this disc in a molding process to provide the raw plastic discs with the information encoded on one of its surfaces.
Following the molding of the discs, it is important that the discs be metalized in which the discs are provided with a thin coat of aluminum over the physical patterning on the surface of the disc. After metalization, the discs are spin coated to cover the disc with a protective coating such as lacquer. This is usually followed by an inspection step.
While prior compact discs were fabricated in a batch process in which individual discs were taken from station-to-station, present processing requires a linear flow of the discs from start to finish so that as many as 1,000 discs per hour can be manufactured.
Aside from the time consuming process of premastering, mastering, electro-plating, and molding, the metalization step has caused significant throughput and quality problems in the past. Specifically, with a single magnetron source and a single vacuum chamber having a single load lock, first the metalizer was located off-line due to its size and complexity. Most importantly however, since these units were single port devices, they could not conveniently be located in a flow line, but rather had to be located off to one side with considerable materials handling problems and complexity. Moreover, the indexing software, while simplified in the single magnetron metalization machines, requires more complication when addressing the indexing needs associated with double port, double magnetron machines used to increase the throughput.
The problems of increasing throughput while maintaining quality were also severe when attempts were made to increase the metalization speed through increasing the rate of deposition. Aside from utilizing deposition sources which were exceedingly high energy consumption devices, the increased energy in the deposition resulted in substrate pitting in which the geometry of the surface of the plastic substrate was altered, with a corresponding alteration in the quality of the information that was readable from the disc.
In terms of prior art CD vacuum metalizers, one such machine is available from Leybold in Germany and the other from Balzers located in Lictenstein. Both of the CD vacuum metalizers from these companies are essentially similar in design and throughput performance. Both metalizers have rotational transport mechanisms through the utilization of a dial inside of the vacuum chamber for the transportation of a plurality of substrates under a single deposition source which includes a magnetron. Adjoining the vacuum chambers for both metalizers are external rotational transport mechanisms for bringing the substrates in and out of the vacuum chamber through a single vacuum lock. Internal and external transport mechanisms move in a sequence to allow for loading and offloading of the substrates.
There are a number of problems associated with these CD vacuum metalizers due to the utilization of a single magnetron. In order to increase throughput, Leybold introduced a double magnetron, double vacuum lock system for the purpose of theoretically increasing the throughput twofold. However, these machines require that the disc exit the same vacuum lock it entered which results in inordinate indexing complexity. The double lock configuration of the Leybold machine also requires that the machine be off-line. This is a problem for linear direction flow, as the metalizer cannot be conveniently inserted into the production line.
Secondly, the Leybold machines have exceedingly large diameter dials exceeding five feet in some instances. The sheer size of the vacuum deposition chamber to accommodate such a large dial prevents its insertion into the production line, to say nothing of the cost of the relatively large unit. In terms of the flow of product, the Leybold double magnetron machines require a double index step in which odd numbered discs are processed by one magnetron whereas even numbered discs are processed by the second magnetron. It will be appreciated that for indexing errors of any magnitude and because each of the discs has to flow under a magnetron not assigned to its metalization, when indexing errors occur, CD titles are mixed up such that all of the mixed up discs must be discarded, as there is no way of identifying which disc was associated with which title. Thus while the double magnetron, double vacuum lock systems permit processing of multiple titles simultaneously, the indexing problems are so severe that the entire lot has to be thrown out for a small indexing error. Note that for 24 substrate holder machines, an indexing error of a few degrees throws off the entire process.
It will be appreciated that for compact disc production, orders for the compact discs are in the hundreds as opposed to thousands or tens of thousands. Thus, it is very important to be able to process different titles simultaneously to maintain the efficiency of the entire line.
Moreover, plaguing the industry is a phenomena called spindle integrity. When titles are to be processed, the discs with one title are loaded onto a single spindle, with an average of six spindles being utilized during a run. These spindles each typically hold as many as 200 CDs. If during the process indexing problems occur, then the entire lot may have to be discarded because the manufacturer must guarantee that the discs loaded on a given spindle come out with the same titles. The inability to guarantee such production is catastrophic. Customer returns for titles that are mislabeled because the content is unknown caused the industry to go from a batch manufacturing process in which mistakes were commonly made, to an in-line approach where title integrity control could be more carefully regulated. The in- line process permits only one title to be run at one time through the molding, metalizing, spin coating, and inspection process. However, the overall investment is higher due to the requirement of assigning one metalizing machine to each molding system. The higher cost in general was warranted by the higher yield since very little of the product had to be discarded, with none having to be discarded due to title integrity.
It will be appreciated that the in-line, single title processing system was not advantageous since although the title integrity was guaranteed, production runs of multiple titles were precluded.
There is therefore a necessity for providing an in-line system with efficient metalizing in which indexing problems are reduced to a minimum while at the same time being able to process multiple titles thereby to accommodate short production runs.