I have a relatively simple product that is a single 10×10 cm PCB in a metal enclosure, and currently the quality control just consists of functional tests and visual inspection of the board. I have only sold less than 100 units but already saw 2 defects in the field. The units were all tested prior to shipping and arrived defective at the customer, so the damage is due to bad solder joints.
Is shock & vibration testing every unit typically the solution or do most manufacturers rely on AOI/visual inspection?