A lead coplanarity inspection system for surface mounted devices

The ever increasing integration level of VLSI devices results in SMD packages with very large pincounts and very small pitches. This evolution sets tremendous challenges to the assembly process. The allowable tolerances on component production and placement equipment are getting much tighter and at the same time leads am becoming more vulnerable. Especially, the non coplanarity of the leads is one of the biggest threats to a good electrical and mechanical connection. Therefore, these components have to be inspected, using a vision system, on the equipment where they are produced as well as on the PCB assembly machines. In fact, on many different machines such as fortrim-and-form, lead straightening, electrical testing, etc. There is a need for such an inspection. In thispaper, ICOS presents a new technique for measurement of leads of a SMD component in three dimensions, using a CCD camera and a special optical system's technique is based on a patented dual shadow projection method. Main features of this method are high accuracy, high speed, compactness and easy to integrate set-up. The paper will explain in detail all these features and will make a comparison with the common multiple camera and laser systems. Greyvalue processing and extreme subpixel accuracy, as well as the special image aquisition module, are key elements of this method. The last part of the paper will cover the integration of this inspection system on different production machines and more specifically on a dedicated lead inspector machine.