Drop impact simulations for lifetime assessment of PCB/BGA assemblies regarding pad cratering

Abstract

In automotive electronics, complex automotive functionalities are managed by car's computers such as electronic control units (ECU). Albeit extremely rare, accidental drop impacts may occur during transportation or mounting ECUs on automobiles, damaging the built-in printed circuit board (PCB)/ball grid array (BGA) package assembly. However, due to larger package dimensions together with heavy components such as capacitors mounted on the board surface, higher acceleration and stress levels can be achieved on ECU electronic components than on hand-held electronic devices during a drop impact. In such cases, the board level drop test methodology defined in the Joint Electron Device Engineering Council (JEDEC) standard needs to be modified in order to match the requirements in automotive applications. The experimental setup used in this study includes a test board clamped between two aluminum frames with the help of screws, in order to reproduce the real clamping conditions of the PCB in an ECU. Furthermore, the new board design allows mounting additional masses at the center of the PCB to take into account the effect of the mass of electronic components present in real ECUs. In this work, the mechanical behavior of PCB/BGA assemblies used in automotive applications when subjected to drop events is assessed. Numerical simulations of the board behavior are performed in order to analyze the transient structural response of the PCB and evaluate the local stresses on the board/joint interface responsible for pad cratering. By varying the loading conditions, different stress levels can be achieved on the PCB laminate directly under the solder joints and a stress-life curve for predicting the assembly lifetime is hence established.