Experimental and numerical verification of fatigue life estimation for solder bumps

Fatigue life estimation of solder bumps is one of the most critical technol ogies for the development of ball grid array packages. In this study, mecha nical fatigue tests were carried out using Sn63-Pb37 solder bump specimens. The cracks were initiated along the entire circumference in the vicinity o f the interface. The fatigue life estimation of the solder bumps was perfor med based on the elastic-creep finite element method (FEM) analysis. It was clear that the strain concentration region coincides with the crack initia tion site. The estimation result for the crack initiation was in good agree ment with the experimental results. The results reconfirmed that it was des irable to employ the equivalent creep strain range occurring at a distance of 50 mum from the singularity point. The life ratio, which provides the qu antitative correlation between the crack initiation and the ultimate fractu re, was determined from the experimental results. The number of cycles to t he fatal failure can be roughly estimated by multiplying the analytical est imation results for the crack initiation by this life ratio. This simple es timation of fatal failure may well be of practical use in actual ball grid array (BGA) design for thermal load conditions.