Streeter, J.P. (1986, ASQC) Norden Systems, United Technologies, Inc., Norwalk, CT
This paper describes one method to minimize a persistant problem that has existed for too long in the electronics industry - the antiquated technique of visual inspection of printed circuit board (PCB) solder joints. Automated solder joint inspection is now possible using the technology developed by Dr. R. Vanzetti, Vanzetti Systems, and presented before the Printed Circuit World Convention III in May of 1984.This technology integrates a laser power source, an infrared detection sub-system, and a dedicated computer into a Laser Inspection System (LIS) capable of providing a totally objective evaluation of solder joint quality. Its operation is based upon the thermal transfer characteristic through a solder joint, and the emissivity of the joints' surface.The detection of a defective solder joint is accomplished by injecting laser energy onto the solder joint for a predetermined length of time. The application of laser power raises the surface temperature above ambient. Then, solder joint acceptability is judged by the LIS computer as a function of its ability to dissipate the thermal energy. The collection of thermal data is accomplished via an infrared detector. The data is transmitted to the LIS computer where the process of digitizing takes place. After receipt of data, the LIS compares the thermal value of each solder joint to a user-designed data bse that contains the accept/reject criteria for every solder joint on the PCB.After a general overview of the LIS, and a comparison of the differences between visual and laser inspection, the methodology of automating the inspection process is addressed. The following items of interest will be described: results of an engineering evaluation project, rationale used to establish the fixed accept/reject criteria, productivity improvements, system deficiencies, the military reaction, conclusions and future plans.