Modelling Of Problems Related To The Temperature Field And Electric Currents In The Intermediate Phases Within Solder Joints

With the trends of miniaturization and the requirements of better performances for electronic products, the volume of solder joints continuously decreases, and their reliabilities cause more and more concerns. One of the major cause for the failure of solder joints is the growth and coalescence of voids within the intermediate phases at solder joint interfaces. Thus, it is of great significance to study the migration and calescence of voids in order to improve the reliability of solder joints and prolong the service life of electronic products.In this paper, taken into account the effect of temperature gradient in solder joints, a diffuse interface model with the finite difference method is used to simulate the growth and migration of voids in intermediate phases under the influence of the interfacial energy of voids and an externally applied temperature gradient. In addition, using the finite element method, a steady state equation of the temperature field including the effect of Joule heating due to the currents in joints is considered. The influences of the size of solder joints, defects and the magnitude of current densities on the distribution of temperature field within the solder joints are discussed. Simulation results show that:(1) In the case of a single void, when the size of void and growth rate remain constant, the presence of a temperature gradient accelerates the migration rate of the void, but has no effect on the void growth rate. A larger temperature gradient results in a larger migration rate of the void. When the size of the void and temperature gradient remain constant, and the rate of void growth is too small, the void gradually disappears while migrating under the influence of the heat flux. To a certain extent, heat flux can heal voids in the solder joints. However, when the rate of void growth is above a threshold, the void survives.(2) In the case of two voids, when the sizes of voids and the distance between them remain constant, the temperature gradient does not accelerates the coalescence of voids, but it accelerates the migration rate of voids. When the magnitude of the temperature gradient and the distance between voids remain constant, the larger the sizes of voids, the larger the rate of coalescence of voids, but the size of voids has no effect on its rate of migration. When the magnitude of the temperature gradient and the size of voids remain constant, if the initial distance between the two voids is small, coalescence of the two voids can be achieved; However, if the initial distance is large, the smaller void disappears under the influence of thermomigration and there is no coalescence.(3) The distribution of the temperature field within the solder joint is subject to the influence of not only the size of the solder joint, but also the current density and the size defect within the solder joint. When the size of the solder joint is small, the boundary conditions of the temperature field play an important role in the distribution of the temperature field within the solder joint. The influence of Joule heating on the distribution of the temperature field becomes more important when the solder joint size is larger. Moreover, the size of defects within the solder joints has a greater impact on the temperature distribution of solder joints when the solder joint size is large. The larger the size of the defects, the larger the highest temperature within solder joints. When the size of the defects within the solder joints is constant, the highest temperature within the solder joint increases with the increase of the current density.