Abstract
Fatigue life estimation of solder bumps is one of the most critical technologies for the development of ball grid array packages. In this study, mechanical fatigue tests were carried out using Sn63-Pb 37 solder bump specimens. The cracks were initiated along the entire circumference in the vicinity of the interface. The observation results suggested that the fracture surfaces were of the intergranular creep type. The fatigue life estimation of the solder bumps was performed based on the elastic-creep FEM analysis. It was clear that the strain concentration region coincides with the crack initiation site in the vicinity of the interface. The estimation result for the crack initiation was in good agreement with the experimental results. The results reconfirmed that it was desirable to employ the equivalent creep strain range occurring at a distance of 0.05 mm from the singularity point. The life ratio, which provides the quantitative correlation between the crack initiation and the ultimate fracture, was determined from the experimental results. The number of cycles to the fatal failure can be roughly estimated by multiplying the analytical estimation results for the crack initiation by this life ratio. This simple estimation of fatal failure may well be of practical use in actual BGA design for thermal load conditions.
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