The idea of SPC is to measure the quality characteristics of a process on a regular basis, use statistical methods to analyze them, and use the results of the analysis to control the process. These combine to help discover and repair the weak point(s) in a process.
However, SMT receives different consideration. The typical understanding of SPC assumes that it is possible to measure the relevant quality characteristics directly on the product. That is not a typical scenario in an SMT process because of the following:
- The SMT process is a chain process with many interactions.
- There are many quality characteristics in the process that are difficult or impossible to measure and to use for process improvement into the process such as x/y accuracy of the printed deposits or placed components requires a suitable measurement method to collect valid data.
- At the final product, the quality characteristics are attributive, meaning either the PCB works or it does not. There is not much opportunity to use the information to find out what part of the process caused a problem and how to fix it.
- The quality characteristics provide only limited information for process optimizations.
- Numerous SMT productions work with high mix/low volume, so even if there is useful process information from the final test, that information will not be available in time.
To solve these problems CeTaQ recommends a double strategy for SPC in SMT:
- Use Machine Capability Analysis to regularly verify equipment performance. This allows control of the equipment�s systematical influences on the production process.
- Implement and monitor random influences of materials, parts and solder paste either through manual tracking or with automated SPC processes.
CeTaQ measurement methods are able to provide the necessary information to keep production equipment under control. For more information, visit the company�s Web site at http://www.cetaq.com.
Headquartered in Germany, CeTaQ GmbH provides a unique combination of products and services throughout world for measuring accuracy and repeatability. As a result, CeTaQ has become highly recognized as the leader in machine capability knowledge and as one of the most desired partners within the last several years in Europe, the Americas and overseas. For more information, visit the company�s Web site at http://www.cetaq.com.