Visual Inspection of Surface‐mounted Solder Joints

Electronics manufacturing throughout the world now uses an increasing percentage of Surface Mount Technology (SMT). The compact and light‐weight surface‐mounted components offer a number of advantages to manufacturers. Unfortunately, however, these same beneficial characteristics make the quality of the product difficult to guarantee. As miniaturisation continues, the inspection problem becomes worse, and so advanced methods of inspection are required. Automatic inspection systems already exist, although an effective, inexpensive and reliable system has yet to be found. Recent work carried out within the Coherent and Electro‐Optics Research Group at Liverpool Polytechnic has looked at the feasibility of applying some of its established inspection methods to the problem of solder joint inspection. Extensive development must still take place; however, the methods employed have shown promise. The system uses structured light techniques to add height information to an image of the solder joint under inspection. In this way a 3‐D image of the joint may be built up, digitised and processed in a computer at high speed in order to determine its quality.