New Methodology Assessment of Copper Trace and Solder Joint Fatigue Failures in Board-level Random Vibrations for Automotive Applications

When assessing mechanical influences such as random and sinusoidal vibration on printed circuit board assemblies (PCBAs) containing ball grid array (BGA) components, major focus is usually placed exclusively on the durability of the solder joints. In the case of lead-free solder joints, such as SAC305, however, we have found that copper traces emanating from the solder pad can also be prone to failure. In continuation of the study initiated by the JEDEC JESD22 working group, it was possible to determine through various failure analysis (FA) techniques the presence of the two competing failure modes that are dependent primarily on the design of the test vehicle (possibly its geometry such as side length of the printed circuit board) and less likely on the vibration type (either sinusoidal or random) or its profile. These findings have led us to reassess and reinterpret test-to-failure results presented previously and introduce additional level of detail into our finite element model. The cyclic bending of the two test vehicles (one containing small square PCB with 77mm side-length vs. big PCB with 140mm side length) subjected to white noise random vibration of 6.27 gRMS were originally modeled with 3D elastic high-cycle fatigue small deformation that ignored the presence of any of the copper traces. Due to the complexity of the geometry, a lumped method was developed to characterize these failures, and preliminary model constants for SAC305 solder joints and copper traces were estimated by ensuring that they were simultaneously compatible with test-to-failure data and fatigue curves for both materials. The important impact of this study includes insight into copper trace and SAC305 solder joints failure in PCBAs subjected to random vibration, FA techniques used to isolate such failures, the development of a simplified quantitative model used in predicting failure occurrence, and validated guidelines to prevent such failures in the design.