Thermal fatigue strength estimation of solder joints of surface mount IC packages. 2nd Report; Comparison of three types of leads.

Abstract

Long-term reliability againt thermal fatigue is required for solder joints of surface mount IC packages. This study is carried out in order to estimate the thermal fatigue strength of the solder joints of three types of leads, namely, batt, gull-wing and J-bend leads. Strain on the solder joint induced by thermal expansion mismatch between the package and substrate has been analyzed by considering elastoplastic behavior of the solder and by treating leads as rigid frames. It is found that the fatigue lives of these types of solder joints can be estimated based on the equivalent plastic strain range calculated by the present analysis. The maximum fatigue lives of the solder joints agree approximately with the fatigue lives of the bulk solder speciments. The fatigue strength of the solder joints depends on the lead and solder size, and the comparative meris of these leads for fatigue strength cannot be discussed unconditionally.