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Effect of delamination on the thermal fatigue of solder joints in flip chips

This paper describes a study of the effects of a delamination at the silicon/underfill interface on the fatigue life of the solder joints of a flip chip. It was first shown that it is important to consider creep deformation during the ramp times, in order to capture the deformation of the solder joints correctly. The effect of the size and location of typical delaminations in a flip chip assembly was then studied. A total of seven cases were simulated using three-dimensional finite element models. These consist of a baseline case with no delamination, and six other cases with different delamination sizes and locations. The fatigue life of the most critical solder joint was found to vary nonlinearly with delamination size and exponentially with distance between delamination and solder joint. It has been established in the literature that the most critical solder joint in a flip chip assembly is the outermost one. However, it was found in this study that the presence of a delamination near another solder joint can cause that particular solder joint to become the most critical one in the flip chip assembly.