Board Level Dynamic Response and Solder Ball Joint Reliability Analysis under Drop Impact Test with Various Impact Orientations

Portable electronics, such as notebooks, cameras and cell phones, can be easily dropped by our miss handling. To mimic the real dropping, drop tests are usually used to study the dynamic response of Printed Circuit Board (PCB) as well as the reliability of the solder ball joints in laboratory. The reliability of solder ball joints is a critical issue since the whole device may be losing functions or failed by disconnection of one single solder ball joint between a chip and a PCB. The main purpose of the present study is to investigate the dynamic response of PCBs and the failure mechanisms of solder ball joints in BGA under board level drop tests with various impact orientations. Impact orientation is an important variable which determines not only the magnitude of the stress/strain but also the dominant stress/strain component in solder joints [1]. Previous studies mainly focused on the drop test with merely one impact orientation [2]. In the present study, the drop impact tests were conducted with four impact orientations. Owing to the lacking of experimental methods/tools for measuring stress/strain of solder ball joints, Finite Element Method (FEM) is used to simulate the various drop impact test conditions and to predict the stress, elastic/plastic strain and strain rate fields in the solder ball joints array. In the simulation, the drop tests were simulated by commercial FEM software ABAQUS?-Explicit with an adoption of a novel Input acceleration (Input-G) method [2]. The lead-free solder´s rate-dependent material property derived from a Mini-Split Hopkinson Bar technique, which was developed in our laboratory, is applied in the present modeling. After verified by experimental results, all the information on stresses, strains and strain rates are very valuable in investigating the failure mechanisms of solder joints under various impact conditions. For instance, the dominant stress/strain components found from the simulation results can be employed to study t- he failure mechanisms with different impact orientations; and the strain rate fields in solder joints are used to compare the drop test with our previous study of the single solder ball shear impact [4].