Comprehensive Modeling of Stress-Strain Behavior for Lead-Free Solder Joints under Board-Level Drop Impact Loading Condition

Board level drop testing is an effective method to characterize the solder joint reliability performance of miniature handheld products. In this study, some drop testing results were summarized based on our previous board-level drop tests. And then the finite element modeling and simulation were conducted to investigate and understand the drop reliability of lead-free solder joints by considering different factors. The strain-rate dependent material properties for lead-free solder has been developed by us and successfully applied in FEA simulation. The important finding of this study is that the constitutive model used has a major impact on dynamic response of solder joint stress and strain results. It was expected that the strain-rate dependent plastic model gave better correlation results than the simple elastic model or bilinear plastic model. In addition to solder material properties, many other factors, including package locations on the PCB, boundary conditions, input-G level, PCB thickness and solder materials, were also simulated to investigate their effects on stress strain performance of solder joint. Comparing to clamped boundary, the 4-screw support condition leads to higher stress level in solder joint. Higher input G-level results in higher solder stress due to larger inertial force and deflection effects on solder joint. The thinner PCB and softer solder can improve the drop performance of board-level electronic assembly.