Y. Hara et al., AUTOMATED INSPECTION OF PLATED THROUGH-HOLES FOR PRINTED-CIRCUIT BOARDS, International journal of the Japan Society for Precision Engineering, 28(4), 1994, pp. 362-367
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.