Design of Machine Vision Systems for Improving Solder Paste Inspection

The quality of solder joints is a crucial aspect on circuit card assemblies containing fine-pitch, surface mount technology (SMT) components. Modern aerospace equipment manufacturers are therefore implementing machine vision systems for the inspection of their electronic products. These methodologies offer many process improvements including faster cycle times, early defect detection, and the ability to efficiently track statistical data. This paper discusses machine vision systems for dimensional verification of solder paste deposited on printed circuit boards. The intent is to show that by focusing on vision inspection early in the assembly process, defects can be detected prior to component placement and solder reflow. Example vision systems and methodologies will be described for applications involving SMT assembly processing. Specifically, various cost-effective techniques for measuring solder paste height and volume will be presented as a means of maintaining solder joint quality. Verification of the aforementioned dimensional attributes is currently very important in the aerospace electronics industry as smaller SMT package and lead sizes are migrating to production.