Modern high-tech PCBAs can potentially have 20,000–30,000 solder joints, requiring sophisticated automated inspection techniques to efficiently inspect results and provide process control feedback. But how do we control the efficiency and effectiveness of the test process itself?
Selecting a Test Strategy – The first step in selecting the proper test strategy for a particular PCB is defining the estimated fault spectrum. We use the PCOLA/SOQ method defined by Agilent to classify the most common types of defects. PCOLA (Presence, Correctness, Orientation, Live, Alignment) refer to attributes of the component. SOQ (Short, Open, Quality) refer to attributes of the solder joint. Together, they test structural integrity of the assembly.
A Complementary Test strategy endeavors to test for each PCOLA/SOQ element just once on the most efficient test platform, where efficiency takes into consideration both runtime and programming time. In a high-mix environment we typically deploy automated optical inspection (AOI), automated x-ray inspection(AXI), and flying probe (FP). By endeavoring to minimize test element overlap, we minimize both programming and runtimes.
As PCBs become more complex and time-to-market pressures make the manufacturing process increasingly difficult, it’s important to look for any and all ways to drive down costs and raise productivity. Through the implementation of an appropriate complimentary test strategy, you will be able to lower your DPMO and create a system of quality control that will maximize the efficiency of your test strategy.
Further Reading: What is the PCOLA/SOQ Complementary Test Strategy?