CLOSED-LOOP QUALITY-CONTROL IN PRINTED-CIRCUIT ASSEMBLY

Almost 30-50% of fabrication costs in electronics production are cause d by testing and repair operations. The reasons for that problem are m any. First of all, there is still a lack of knowledge concerning the c onditions for robust process control. On the other hand. uncertain spe cification of product quality causes unnecessary inspection, testing, and repair actions. Thus, a strategy for yield improvement requires st rong dedication to causal relationships and specification of process a nd product quality. In the first step, critical process parameters and their causal effects on product quality must be analyzed. In the seco nd step, once critical process parameter are addressed, control strate gies can be developed to assure high first pass yields. This paper giv es an overview of ongoing work that has been performed to establish a SMT production line with closed loop quality control via direct proces s monitoring capabilities and integrated inspection operations. For di fferent inspection tasks, 3-D laser and x-ray inspect on is applied. P rocess parameters as well as test and inspection results are gathered on line. Thus, interrelationships between different process steps, beg inning from material inspection, solder paste application, components placement, reflow soldering, and final inspection, can be analyzed. Mo reover, variation of process parameters conforming to different approa ches to design of experiments (DOE) can be performed while running pro duction. On-line diagnosis of process parameters and inspection result s enables a closed loop quality control.