A case study of SPC in circuit board assembly: statistical mounting process control

A system was developed to continuously monitor the cycle times of successive placement machines in a long high-speed surface mount line. Statistical process control software was created to generate predefined out-of-control alarms when an unexpected change is monitored in the cycle times. The developed Statistical Mounting Process Control application was divided into three monitoring levels: line performance view, machine performance view, and pickup performance view (i.e, component feeders and nozzles). Most of the problems causing unexpected increase in placement cycle time are directly related to bad performing feeders or nozzles. The data transfer between the machines and host computer system is described. Out-of-control criterias selected for this statistical process control application are discussed in detail. One typical out-of-control situation is described for fast action and response to get the placement - process back to right track again. Promising results were observed after several weeks of evaluation of the system in two production lines: component pickup errors were decreased about 50%. In the future this is expected to have a direct positive impact on the output of the factory as well as on the total material cost and unexpected shortages, because component waste is simultaneously decreased. A theory is also discussed about poor pick-up performance having possible negative effect on the placement accuracy.