A Study of Factors Affecting Solder Joint Fatigue Life of Thermally Enhanced Ball Grid Array Assemblies

In this study, a finite element study of design factors, including material constants and geometry parameters, affecting fatigue life of solder joints of a typical cavity-down Thermally Enhanced Ball Grid Array (TEBGA) assembly subjected to an accelerated temperature cycling load is performed. In order to precisely characterize the fatigue life of solder joints, the geometry profile of solder joints within the package is substantially predicted using an energy-based method-the Surface Evolver (see, e.g., Brakke, 1994; Chiang et al., 2000). In addition, a finite-volume-weighted averaging technique is proposed to describe the strain/stress response of solder joints at material/geometry discontinuities. The analysis employs a plane strain FE model with the purpose of reducing the computational cost. To validate the FE modeling so as to corroborate the nonlinear and complex mechanical behaviors of materials in the assembly, a typical interferometric displacement measurement method-Moire interferometry (see, Han and Guo, 1995) and 3-D solid modeling are used. Through the parametric design of the fatigue life of solder joints, the reliability characteristics of the TEBGA assembly are then effectively identified.