Pbga Package Thermal Reliability Analysis And Structural Optimization

Thermal-stress failure of package is the main part effecting the reliability of electronic devices. The finite element numerical simulation model had been established for a plastic ball grid array (PBGA). An unified viscoplastic constitutive law, the Anand model was applied to represent the inelastic deformation behavior for solder. Distribution of thermal stress and strain of the package which subjected to thermal cycling loading were simulated and analyzed. Fatigue life of the package was predicted using the Coffin-Masson equation modified by temperature and frequency. The numerical analyses provide database for improving reliability of package and optimum design. The specific details are as follow:(1)The stress and strain distributing rule of the package and solder joints was analyzed in five different thermal cycle loadings of IPC9701 standard, the fatigue life of the package was predicted, and effects of thermal cycle parameters were compared on thermal fatigue life of PBGA. The results show that: the distribution of the thermal stress and strain in PBGA package is similitude after different thermal cycle loadings; solder joints are the most dangerous points of package structure failu(?)e; the fatigue life of package is related with the thermal cycle temperature rang, the maximum dwell temperature and thermal cycle frequency; the maximum shear plastic strain closely relates to the maximum dwell temperature and the thermal cycle dwell time.(2)Optimization and design of the PBGA package structure and solder joints. The length of silica and the thickness of substrate were changed to research the dimension effect. The results show that the fatigue life increases as the length of silica increases, it is beneficial to improve the reliability and to reduce the ratio of the package size and the chip area. The fatigue life decreases as the thickness of substrate increases. The height, diameter and material of the solder joints were also changed in order to observe their effects on the thermal fatigue life of the package. The results are acquired as follow: the fatigue life is increased as the height of solder joints increase, the fatigue life debases as the diameter of solder joints increase, the effect of height is bigger than diameter. Lead-free solder material Sn96.5Ag3.5 and Sn3.8AgO.7Cu can enhance the fatigue life of package comparing with solder Sn63Pb37.