AUTOMATED INSPECTION OF PLATED THROUGH-HOLES FOR PRINTED-CIRCUIT BOARDS

This paper describes a system which automatically inspects defects in plated through-holes formed in muli-layed printed circuit boards. Thes e defects are the types of which a part of copper is lacking on the pl ated through-hole. In order to detect the defects, the system utilizes fluorescent light emission from the base materials of the boards. The through-holes are illuminated with a green light. The system detects defects by sensing the fluorescent light with an ultra-high sensitivit y detector. If there are any defects, i.e., if there is any part of ba se material exposed, the materials emit red fluorescent light. It has been proved that the system can detect circular voids as small as 150 phi mu m, or voids with a surface area bigger than 150 mum.