The microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. In our prior work on aging effects (Ma, et al., ECTC 2006), we demonstrated that the observed material behavior variations of SAC405 and SAC305 lead free solders during room temperature aging (25°C ) were unexpectedly large and universally detrimental to reliability. Such effects for lead free solder materials are much more dramatic at the higher aging temperatures (e.g. 100-150°C) typical of the harsh environments present in high performance computing and in automotive, aerospace, and defense applications. However, there has been little work in the literature, and the work that has been done has concentrated on the degradation of solder ball shear strength (e.g. Dage Shear Tester). Current finite element models for solder joint reliability during thermal cycling accelerated life testing are based on traditional solder constitutive and failure models that do not evolve with material aging. Thus, there will be significant errors in the calculations with the new lead free SAC alloys that illustrate dramatic aging phenomena.In the current work, we have explored the effects of elevated temperature isothermal aging on the mechanical behavior and reliability of lead free solders. The effects of aging on mechanical behavior have been examined by performing stress-strain and creep tests on SAC405 and SAC305 samples that were aged for various durations (0-6 months) at several elevated temperatures (80, 100, 125, and 150°C). Analogous tests were performed with 63Sn-37Pb eutectic solder samples for comparison purposes. Variations of the temperature dependent mechanical properties (elastic modulus, yield stress, ultimate strength, creep compliance, etc.) were observed and modeled as a function of aging time and temperature. In this paper, we have concentrated our efforts on presenting the results for samples aged at 125 'C. In addition, the new elevated temperature aging data were correlated with our room temperature results from last year's investigation.The results obtained in this work have demonstrated the significant effects of elevated temperature exposure on solder joints. As expected, the mechanical properties evolved at a higher rate and experienced larger changes during elevated temperature aging (compared to room temperature aging). After approximately 200 hours of aging, the lead free solder joint material properties were observed to degrade at a nearly constant rate. We have developed a mathematical model to predict the variation of the properties with aging time and aging temperature. Our data for the evolution of the creep response of solders with elevated temperature aging show that the creep behavior of lead free and tin-lead solders experience a "cross-over point" where lead free solders begin to creep at higher rates than standard 63Sn-37Pb solder for the same stress level. Such an effect is not observ...

No abstract

No abstract

Drop-induced failures are most dominant in portahle electronic products. In this &dy; explicit fmite element models ,have been used to study the transient dynamics of printed circuit hoards during drop from 6ft. Methodologies for modeling components using smeared property formulations have been investigated. Reduced integration element formulations examined. includeshell and solid elements. . Model predictions have been validated with experimental data. Results show that models with smeared properties can predict transient-dynamic response of hoard assemblies in drop-impact, fairly accurately. High-speed data acquisition system has been used to capture in-situ strain, continuity and acceleration data in excess of 1 million samples per second. Ultra high-speed video at 40,000 fps per second has been used to capture the deformation kinematics. Component types examined includeplastic hall-grid arrays, tape-may BGA, QFN, and C2BGA. Model predictions have been correlated with experimental data.Impact of experimental error sources o n , model correlation with experiments also has been investigated 0-7803-83656/04/$20.00 WOO4 IEEE

No abstract

No abstract

No abstract

No abstract