Anisothermal Fatigue Analysis of Solder Joints in a Convective CBGA Package Under Power Cycling

Abstract

This paper presents the use of an integrated flow-thermo-mechanical analysis method and tools for numerically studying the effect of local heat transfer coefficient on anisothermal cyclic fatigue behavior of solder joints in a CBGA (ceramic ball grid array) package under power cycling. A cyclic chip power load of 1 watt to 10 watts at a frequency of 5 cph (cycles per hour) with an air flow speed of 0.5 m/s was used to simulate a typical field condition for a 32mm CBGA air cooled package. Temperature dependent viscoplastic properties of Pb-Sn (lead-tin) alloys were used to model the solder joint behavior in the package. An approach using the Δϵeqin-modified Coffin-Manson Law was applied to estimate the fatigue life of the solder joint. The Δϵeqin represents a saturated equivalent inelastic strain range as determined by the finite element model. The results of anisothermal deformation and fatigue response of solder joint are compared to that of a condition of constant temperature cycling.