Random Vibration Reliability Analysis And Research On Solder Joint Of PBGA Board Level Assembly

In the process of transportation and other field applications, PBGA board assembly was easily affected by various random vibration factors, which leaded to high-cycle fatigue failure of solder joint. The application environment of electronic product becomes more and more severe, which will intensify elastic-plastic deformation of assembly's solder joint, and cause fatigue damage rapidly cumulative, and finally result in failure of solder joint and even device. Therefore, the dynamic characteristic of PCB assembly and vibration reliability of solder joint becomes one of the focus points of the reliability.In order to explore the dynamic characteristic of board assembly, the PBGA assembly test samples which contain daisy chain patterns was designed. Different fixed methods, such as four screws fixation, six screws fixation and two end fixation, were used, and the modal parameters were obtained through modal test and finite element method respectively. After correctness was verified by FEM model and simulation method, the effect of each fixation methods on the first natural frequency of PCB assembly was analyzed. Based on the consistency of the verification of modal simulation and test result consistent, typical fixation method was selected, and random vibration test and simulation of PCB assembly were done. Through random vibration test, most vulnerable to vibration failure of solder joint was confirmed. Based on the random vibration simulation, the maximum stress and strain region was confirmed and the simulation results were compared with the test, and then the model correctness was verified again. Solder joint life prediction method under random vibration environment was proposed. Finally, through modifying the parameters, such as solder joint's material, diameter, height, PCB's thickness and fixation condition, modal and random vibration simulation were done. The effect of these parameters on vibration stress and strain of solder joint was researched.Results show that first natural frequency of the PCB assembly increases with the increase in fixed support points. The critical solder joint located on the outmost corner of PBGA which is far away from the fixed points, it is good agreement the first failure solder joint from the vibration test. The crack failure of critical solder joint occurs in the solder close to the device side. Voids in solder joint have harmful influence on the vibration reliability of solder joint. The SMD pad is easier to cause the stress concentration of solder joint comparing to NSMD pad. It can be reduce the maximum stress of solder joint through reducing solder joint height, increasing the solder joint diameter, increasing the thickness of PCB and increasing the numbers of fixation point. It is found that the lead free solder joint has more vibration stress compared with SnPb solder joint. The stress-strain response of interest region could be obtained through the random vibration simulation. Our research results are beneficial to guide the soldering process, to improve structural design, and to analyze the effect of solder joint parameters on the maximum von mises stress. It can also be used as references for increasing vibration reliability of solder joint.