Statistical process control in PCB manufacture: what are the lessons?

A number of printed circuit board (PCB) manufacturers perceive that they face difficulties in the application of statistical process control (SPC). The difficulties include the product characteristics and process parameters to be measured and charted, the mix of different manufacturing technologies, the inherent variability of the chemistry used in the process, the interconnecting nature of the processes, small batch production runs, and the concept of performance-based charts. The authors report and examine the most common queries raised by representatives of the industry under the broad headings of: application, type of control chart and its design, interpretation and capability.