A generalized multi-domain Rayleigh Ritz (MDRR) stress analysis model has been proposed earlier by the authors [Ling, et. al. 1996] to obtain the stress and strain field in surface-mount solder joints, under cyclic thermal loading condition.Elastic, plastic and time-dependent viscoplastic analysis has been demonstrated on BOA solder joints. The analysis results confirm that the MDRR technique is capable of providing stress, strain hysteresis with adequate accuracy, without time consumingfinite element model generation and analyses.The MDRR stress analysis approach is general in principle for various surface-mount interconnects. By choosing appropriate mapping function, different physical configurations are replaced by identical fictitious domains. The rest of the analysis thus canbe carried out in an invariant manner. In the current paper, the MDRR technique is applied to BOA solder joints, under thermomechanical loading environments. Specific isoparametric mapping functions are chosen to map the unique geometry outline of a BOAelectronic package assembly. The eutectic solder layer surrounding the highlead solder ball is modeled by colonies of sub-domains at corners of the solder domain. Eutectic solder joint and high-lead solder joint material properties are assigned atdifferent solder joint regions accordingly. Polynomial displacement fields are assumed in the fictitious domain and the total potential energy is calculated and minimized in the same fashion as for J-leaded solder joint stress analysis. Stress contoursare generated in the BOA solder joints under thermomechanical loading. Additional stress and strain hysteresis is obtained for non-linear thermomechanical loading. All results are compared with finite element analysis results for the same loadingcondition.
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