The investigation of defect screening methodology using mechanical stress test for Pb-free module product

The major purpose of the mechanical stress screening is to screen out the products which have potential defects which lie in materials, design, process, and operation etc. If the screening is thorough before the products are shipped, the rate of the abnormal failure at the users' side can be eliminated or lowered significantly. The manufacturing lot which goes through appropriate screening will have better reliability and meanwhile have less issues of repair, which achieve the goal of cost effectiveness. The thermal cycling and random vibration are two common methods used in stress screening test. The 50%~80% of the product limit which is acquired after the high accelerated life test (HALT) in the design phase is applied to the products by the highly accelerated stress screening (HASS) after the design phase. Solder joint defect is one can pose a significant risk in modules if the design, lead-free assembly, and handling processes are not carefully controlled. For the reasons mentioned above, it takes further investigation to learn whether the methods applied to the system-level final products are an effective evaluation to screen the solder joint defects in the process. In this study, the random vibration is selected to evaluate whether the defects in the process can be found. The test vehicles, daisy chain lead-free 0.8 mm pitch 60-ball BGA components, were assembled on single MiniDIMM cards where defects are intentionally created in some solder masks. The reflow temperature and solder paste volume are also the factors applied to the modules respectively. After the test is completed, the result reveals that the samples with the solder joint defect failed while normal samples do not fail. Due to the efficiency of the screening conditions vs. defect types, it cannot be firmly concluded that the random vibration is an effective method to screen assembly defects.