How to identify the root cause of SMT cold solder joints in an electronics factory?

For SMT cold solder joints, don't just let the operator perform rework and call it a day. First, check which part number, location, or machine the defects are concentrated on. If they are concentrated near fine-pitch ICs, check the stencil aperture, solder paste condition, and placement pressure; if they are concentrated on one side, it might be the reflow oven temperature zones or board…