Damage Pre-Cursor Based Life Prediction of the Effect of Mean Temperature of Thermal Cycle on the SnAgCu Solder Joint Reliability Pradeep Lall, Kazi Mirza, Jeff Suhling Auburn University NSF-CAVE3 Electronic Research Center Department of Mechanical Engineering Auburn, AL. 36849 Tele: (334) 844-3424 E-mail: lall@auburn.edu Abstract Electronics in automotive underhood applications may be subjected to temperatures in the neighborhood of 150°C to 175°C. Several of the electronics functions such as lane departure warning systems, collision avoidance systems are critical to vehicle operation. Prior studies have shown that low silver leadfree SnAgCu alloys exhibit pronounced deterioration in mechanical properties even after short exposure to high temperatures. Current life prediction models for second level interconnects do not provide a method for quick-turn assessment of the effect of mean temperature on cyclic life. In this paper, a method has been developed for assessment of the effect of mean cyclic temperature on the thermal fatigue reliability based on physics based leading damage indicators including phase-growth rate and the intermetallic thickness. Since the quantification of the thermal profile in the field applications may be often very difficult, the proposed method does not require the acquisition of the thermal profile history. Three environments of -50°C to +50°C, 0°C to 100°C, 50°C to 150°C with identical thermal excursion and different mean temperatures have been studied. Test assemblies with three different packages including CABGA 144, PBGA 324, and PBGA 676 have been used for the study. Damage-proxy based damage-equivalency relationships have been derived for the three thermal cycles. Weibull distributions have been developed for the three test assemblies to evaluate the effect of the mean cyclic temperature on the thermal fatigue life. Data indicates that the thermal fatigue lie drops with the increase in mean temperature of the thermal cycle even if the thermal excursion magnitude is kept constant. Damage equivalency model predictions of the effect of mean temperature of the thermal cycle have been validated versus weibull life distributions. The damage proxy based damage equivalency methodology shows good correlation with experimental data. Introduction Electronics in a variety of applications such as automotive underhood on-engine, on-transmission, high-performance computing, military, and defense applications may be subjected to prolonged exposure to high temperature in addition to wide cyclic temperature extremes. Furthermore, the mean temperature of the thermal excursion may vary based on application. Prior, studies have revealed that leadfree material properties degrade with prolonged exposure to high temperature. Detrimental effects on properties include the degradation in the yield strength and ultimate tensile strength of the materials. [Chou 2002; Hasegawa 2001; Zhang 2009]. Furthermore, prior exposure to high temperature aging has been shown to reduce mechanical integrity by as much as 50-percent. Evolution of mechanical properties has been verified in the solder alloys even at high strain rates in the neighborhood of 1-to-100 sec -1 typical of shock and vibration [Lall 2013]. The effects are most pronounced in the widely used SnAgCu based alloys including SAC105, SAC205, SAC305 and SAC405 solders. Lower silver solders such as the SAC105, often touted for their resistance to transient dynamic shock and vibration, are the most susceptible to thermal aging amongst the SAC solders. Thus, prior data suggests that the cyclic life for leadfree assemblies cannot be considered without accounting for mean cyclic temperature. The evolution of mechanical properties of leadfree solders alloys may pose a potential reliability problem in long-life systems such as automotive applications in which electronics often resides underhood of the car at temperatures in the neighborhood of 150°C-175°C. Several of the electronic modules in automotive electronics applications may perform critical functions such as lane departure warning, collision avoidance, adaptive cruise control and antilock braking. There is a need for tools and techniques to enable damage mapping between different thermal cycle conditions and for evaluating the effect of the mean temperature of the thermal cycle. However, the current, closed form life prediction models for leadfree second-level interconnects do not provide any method for quick-assessment of effect of mean temperature on the expected life under thermal cycling. In this paper, a new model has been developed for the assessment of the effect of the thermal cycle’s mean temperature on the cyclic life of a leadfree assembly. Three ball-grid arrays including CABGA 144, PBGA 324, and PBGA 676 have been subjected to three thermal cycles including -50°C to +50°C, 0°C to 100°C, 50°C to 150°C. The thermal cyclic magnitude has been kept the same while the mean temperature has been varied in the thermal cycle. Previously, leading indicators of damage have been used to quantify the accrued thermo-mechanical damage under steady-state and cyclic temperature exposure in leadfree solders. [Lall 2011 a-b ; 2012 a-b ]. in this paper, microstructural indicators including phase growth in solder interconnects, intermetallic thickness, intermetallic composition has been measured. In addition, a separate population of the parts has been cycled to failure under each of the three conditions. Predictive model has been developed for mapping the cyclic damage for leadfree electronics subjected to mean cyclic temperatures. Model predictions have been correlated with experimental weibull failure distributions in order to quantify 978-1-4799-2407-3/14/$31.00 ©2014 IEEE 990 2014 Electronic Components & Technology Conference