Optimization of inspection strategies by use of quality cost models and SPC

The main goals of quality management are customer satisfaction by delivery of defect free products, and radical reduction of defect rates and quality costs in production. Controlled processes are the most important way to reach these goals. In electronics production, the processes are complex and are subject to many strong environmental influences, especially for production of small batches of assemblies (high mix/low volume). Tools are required to compare the quality behaviors of different technological processes caused by different electronic products and establish the correct inspection strategy: no inspection, 100% inspection or statistical process control (SPC). To answer these questions we have developed simple quality cost models. The quality costs are the system used to compare different inspection strategies. The costs are calculated by the use of mathematical quality cost models. The authors presented "linear" cost models at ISSE 1999 in Dresden. These models also reflect the influence of pseudo defects and defect flow at inspection processes. The quality cost models can be used as a decision aid in test process organization (100% inspection, SPC or no inspection after the considered process). In the case of SPC, it is possible to get an adapted sampling plan. The investigations were made in cooperation with the electronics production of a large international enterprise. The basic quality cost models and the extension for SPC are explained here. The implementation, successful use and economical results of using these models are presented.