Selecting the Optimal Test Strategy

T oday’s printed circuit board (PCB) assembly test engineers face significantly more test challenges than just a few years ago. Board complexity is dramatically increasing with more components, more joints, higher densities and new package technologies. The higher component and joint counts create more defect opportunities, which lead to lower yields for a given defect level. Fortunately, test and inspection methods such as solder paste inspection (SPI), automatic x-ray inspection (AXI) and automatic optical inspection (AOI) have emerged over the past several years. These techniques are providing effective additions to traditional test technologies at in-circuit test (ICT) and functional test. Although these new tools give more choices, they also pose new dilemmas. What is the right test/inspection strategy? And what is the right combination of these tools? Several factors influence what test technologies are the right selection for a particular PCB assembly. These factors include the degree of complexity of the boards, the dominant manufacturing process (no wave, wave, selective wave) and the primary goal of the testing effort—defect containment, process improvement or both.