Reliability analysis for fine pitch BGA package

This paper presents a linear parametric finite element analysis for the solder joints of a fine pitch BGA package for a selection of key design parameters including the effects of substrate, die attach material, and die size. Results show that, when the package assembly is subjected to the temperature excursion, the solder joint stress decreases as the thickness of the substrate increases. A softer die attach material results in higher solder stresses. This observation is different from some existing chip scale packaging due to structural differences. Results also show that the die size plays an important role on the stress/strain in the solder joints. In addition to the linear parametric analysis, a more complex, nonlinear study is also carried out. With this approach, solder joint configurations are predicted with Surface Evolver. Nonlinear solder properties are used to calculate the stress/strain evolution during thermal cycling. The energy approach is used to estimate solder joint fatigue life.