Analysis On SMT Lead-free Solder Joints Reliability Under Random Vibration Loading

At present, the the surface mounting Technology (SMT) are widely applied to the field of microelectronic packaging. With the popularity of some handheld or portable electronic products, it is inevitable to vibrate when we transport them. Along with enhancing of people's consciousness for environmental protection, using lead-free solder will be the development tendency of the microelectronic industry. Because the failure of electronic components is mainly caused by solder joints failure, therefore the analysis on reliability of SMT lead-free solder joint under random vibration loading is very significant.In this paper, the reliability of SMT lead-free solder joints of BGA packages, which are currently popular in handheld electronic products, was investigated under random vibration. A series of experimental and theoretical researches were finished in order to research failure mechanism of SMT lead-free solder joints of BGA packages.First, a series of modal tests were conducted. The modal tests of PCB with different exciting positions and exciting forces using Vibromap1000 system was carrid out and an equivalent finite element model (FEM) was developed to analyse the modes which verified the validation of FEM and determined the fixed boundary condition of FEM. These will help to the following work.Second, random vibration tests of four different power spectral densities (PSD) were carried out. Cross section analysis of failed solder joints was conducted which combined with dynamic voltages to analyse the failure crack. It was found in our random vibration tests that the root cause of lead-free solder joints was the combined effect of vibration and PCB bending. From the dynamic voltages of some test points and cross section analysis, it can be seen that the solder joints at four outermost corners were failed at first. The failure mode of solder joint was changing with the different PSDs.Third, Based on modal tests and finite element simulation, a valid three dimension finite element model was established. The base motion method was adopted and the ABAQUS software was used to carry out the three-dimension FE simulations of lead-free solder joints. The established FEM was very simple and effective, the dynamic responses, such as out-put displacements were well correlated between testing and simulating. When the maximum peeling stress was used as a failure indicator to determine initial failure location of solder joint, numerically predicted failure locations of the solder joints accorded with those observed from random vibration tests.Final, first of all, Weibull distribution in statistics was utilized to analyse the distribution of failure life, which was integrated with Basquin's equation for cumulative damage model of lead-free solder joints base on the maximum peeling stress. Then, Cox proportional hazards model (PHM) is used to evaluate the effect of PSD of in-put acceleration on the solder joints'life span. The distribution of failure life estimated from the PHM was combined with Miner's law to develop an life prediction model which was relate to PSD.