Finite element modelling of a BGA package subjected to thermal and power cycling

The finite element techniques of substructuring and submodelling have been applied to a 9x9 ball grid array in order to estimate the fatigue life of the solder joints under various thermal loading conditions. Darveaux's method, which relates the accumulated viscoplastic strain energy density and crack growth data to fatigue life, has been used in all cases to predict the life of the solder joint. Three types of cycle were considered: (i) isothermal temperature cycling, (ii) isothermal temperature cycling with constant heat generation in the die, and (iii) power cycling (transient heat generation in the die). Results indicate that for the first two cases, the solder joint closest to the centre will fail first and that the superimposed constant heat generation in the die has little effect on fatigue life. In the case of power cycling, the outermost diagonal joint is predicted to fail first. The two finite element techniques examined are shown to produce similar results, however, substructuring is not applied to the power cycling case due to the transient nature of the problem.