It is the core problem of disc replicators to produce discs with best quality while maintaining the specified yield. Especially for BD manufacturing these goals are still not easy to achieve. Continuously developing and improving its solutions dr. schwab Inspection Technology has announced new additions to its well-established inline scanner IQPCblu. For monitoring and controlling environmental conditions inside a production line a Particle Counter and Temperature/Humidity unit has been integrated in this product line.
“Looking at a result presentation of our scanner IQPCblu (see Picture 1) you see the Cover layer thickness for more than 3000 successive Blu-ray Discs of a production line. The diagram shows that, after a short production stop, layer thickness increases significantly after the restart. Besides you will observe that there are periodic thickness changes, ups and downs of more than a micrometer with a period of about 500 discs”, explains Dr. Leonhard Schwab, CTO of dr. schwab Inspection Technology.
|Pic 1: Trend Analysis showing periodic BD Cover Layer Thickness Variations|
“The cause of this being not evident, we compared these data using our Trend Analysis Module with the corresponding temperature/humidity results and found out that this is caused by variations in the surrounding temperature. Visualizing and correlating of two actually autonomous measurement results revealed the reasons of this quality problem. In a closed loop process these results were used as feedback information to control the depending process steps. Thus, quickly returning thickness values to the allowed process window, only a small number of defective discs were produced after the restart.”
“Similar scenarios regarding the increase of surface defects could be correlated with variations of air purity”, Schwab adds. “Combining the event count with the results of the Particle Counter it was easy to identify the main sources for the contamination. The following diagrams (see Picture 2) show an example of measurement results over a period of 15 hours.
|Pic 2: Surface Defects (Top Events) corresponding to Particle Counter Results|
Slightly increasing values for particle count (>3µ and >5µ) correspond to the increasing values of events on the top side of samples. Again we have a clear indication for the reasons of a quality deviation: the linear growth of topside events is caused by rising pollution of the ambient air”.
To clearly identify the cause of such deviations and their influence on the production process, dr.schwab offers an enhancement to its in-line scanner IQPCblu for measurement and correlation of such influencing parameters. The package is composed of the Particle Counter unit and a temperature/humidity device, both connected to the scanner via Ethernet. The Particle Counter operates with vacuum and has an air flow rate of 2.83 l/min. Within this flow rate a maximum concentration of 60000 particles, at a minimum size of 3 µm, is recognized. For temperature/humidity measurement up to 4 sensors can be placed at different locations inside of the production line. Temperature is measured with an accuracy of ± 0.5° and a resolution of 0.01° within a range from -40°C to +85°C.
The data detected for particles, temperature and humidity are fully integrated into the IQPC evaluation software. The trend function displays the changes over time and allows correlating these results with the disc inspection results. Via IQPC database function different measurement quantities can be displayed in one diagram for direct comparison.
Being able to allocate the cause of quality deviations to air purity, temperature or humidity changes this solution provides information about kind, time and location of necessary corrective actions. Improving the features for automated process control and optimization the Particle Counter is another valuable tool to help disc producers meet the exacting production standards required.