Vibration durability modeling and dynamic response analysis of PBGA mixed solder joints

Along with more and more use of high density plastic ball grid array (PBGA) in portable electronic products and military electronic equipments, the vibration fatigue reliability of solder joints for PBGA becomes a critical concern. In this paper, a quarter 3D symmetric model was developed by ANSYS software, then modal analysis of PCBA assembly and random vibration response analysis of mixed solder joints were implemented. The effect of fixation points on mode shape and the size parameters for solder joints on von mises stress were discussed. Finally, the influence of every step mode on the PCB bending deflection was analyzed. The results showed that the first bend mode was the main factor which influences the bend deformation of the PCB. Adopting more fixations can reduce the influence of the first mode. Solder joint with maximum von mises stress (critical solder joint) was occurred on the outmost corner of PBGA which is mounted at the position of PCB largest deformation, and the accurate critical interface was located at the soldering interface between PCB and solder ball. More deflection of PCB causes larger stress of solder joint. The further research found that the first four step natural frequencies are less than 2000Hz, and they are within the vibration frequency range of 5Hz to 2000Hz caused by the transport and application. So it is necessary to optimize the fixation design of PCB assembly. Moreover, within a certain range, the thicker of PCB vehicle can get smaller stress, while the greater height of solder ball would cause greater stress.