Closed loop quality control in printed circuit assembly

Almost 30-50% of fabrication costs in electronics production are caused by testing and repair operations. The reasons for that problem are many. First of all, there is still a lack of knowledge concerning the conditions for robust process control. On the other hand, uncertain specification of product quality causes unnecessary inspection, testing, and repair actions. Thus, a strategy for yield improvement requires strong dedication to causal relationships and specification of process and product quality. In the first step, critical process parameters and their causal effects on product quality must be analyzed. In the second step, once critical process parameter are addressed, control strategies can be developed to assure high first pass yields. This paper gives an overview of ongoing work that has been performed to establish a SMT production line with closed loop quality control via direct process monitoring capabilities and integrated inspection operations. For different inspection tasks, 3-D laser and X-ray inspection is applied. Process parameters as well as test and inspection results are gathered on line. Thus, interrelationships between different process steps, beginning from material inspection, solder paste application, components placement, reflow soldering, and final inspection, can be analyzed. Moreover, variation of process parameters conforming to different approaches to design of experiments (DOE) can be performed while running production. On-line diagnosis of process parameters and inspection results enables a closed loop quality control.<
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