A generalized multi-domain Rayleigh-Ritz (MDRR) approach developed by Ling et al. , is extended in this paper, to obtain the stress field in flip chip solder interconnects, under cyclic thermal loading. Elastic, plastic and time-dependent viscoplastic analysis is demonstrated on flip chip solder interconnects. The method has been applied to other surface-mount interconnects in the past such as J-lead [Ling et al., 1996] and ball-grid joints [Ling et al., 1997]. The analysis results for the J-lead and ball grid joints have confirmed that the MDRR technique is capable of providing stress, strain hysteresis with adequate accuracy, at a fraction of the time required by finite element model generation and analyses. Nonlinear viscoplastic stress analysis results for flip-chip interconnects without underfill are presented in this paper. The effect of the underfill will be presented in a future paper. The goal is to predict the stress, strain and strain energy density distributions in the solder with good accuracy, but at a fraction of the computational effort typically required in a full-scale finite element analysis. The fatigue endurance of the solder joints is assessed by combining results from this stress analysis model with an energy-partitioning damage model [Dasgupta el al., 1992]. The life predicted by the analytical damage model is compared with experimental results.
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