NONLINEAR-ANALYSIS OF FULL-MATRIX AND PERIMETER PLASTIC BALL GRID ARRAY SOLDER JOINTS

The application of Ball Grid Army (EGA) technology in electronic packa ging on high I/O plastic and ceramic packages has grown significantly during the past few years. Although PBGA (plastic EGA) has several adv antages over fine-pitch Quad Flat Pack (QFP) in terms of smaller packa ge area, higher I/Os, lower switching noise, larger pitch, higher asse mbly yield, and improved robustness in manufacturing process, potentia l package reliability problems can stili occur, e.g., excessive solder joint deformation induced by substrate warpage, moisture ingression ( popcorn effect), large variation in solder ball size, voiding as a res ult of flux entrapment and improper pad/solder mask design (Marrs and Olachea, 1994; Solberg, 1994; Freyman and Petrucci, 1995; Lau, 1995; D onlin, 1996; Lasky et al., 1996; Munroe et al., 1996). Regardless of i ts improved thermal fatigue performance over the past few years throug h an extensive amount of research, the EGA solder joint may still pose a reliability issue under harsh environment, e.g., automotive underho od larger package size, or higher temperature and temperature gradient due to increase in power dissipation of the package. Numerous studies in EGA solder joint deformation and reliability under thermal and mec hanical loadings can be found in the literature, e.g., Borgesen et al. (1993), Choi et al. (1993), Guo et al. (1993), Ju et al. (1994), Lau et al. (1994) Lau (1995), and Heinrich et al. (1995). Also, reliabilit y prediction models have been developed by, e.g., Darveaux et al. (199 5) and Darveaux (1996). The present study focuses on the application o f a detailed nonlinear finite element analysis (FEA) to studying the t hermal cyclic response of solder joints in two particular EGA packages , full-matrix and perimeter. Both time-independent plasticity and time -dependent-dependent effect, i.e., creep and relaxation, are considere d in the constitutive equations of solder joint to evaluate the discre pancy in the results of life prediction. The critical solder joint is identified, and the locations that are most susceptible to fatigue fai lure in the critical joint are discussed. Some limitations in computat ion and reliability prediction ale also discussed.