I am assuming that you refer to surface mount technology when you say SMT, and I agree with your previous two posters. Your calculations are the same regardless of the technology at play, and the IPC standards – probably IPC 610 (E – I think it is now) give you the defect types impacting both internal and external acceptance of your process/product. You will/can get into an endless circular debate regarding defects on your surface mounted chip, is it one lead solder defective out of many on a chip at issue or is it a process defect to have one on the board/final assembly – the main thing is to assure criteria selection consistency between the numerator and denominator for your calculation, make it meaningful and stick with it. Benchmark within your industry. If you need more detail, please ask – I had some fun years in aerospace engineering and operations prior to medical products. Good luck.
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