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MAY 2020 I SMT007 MAGAZINE 31 At 500 cycles, the shear strength of the eutectic SnBi and HRL1 has only a small decrease from their initial values of 10.6 and 11.2 kgf, respectively, whereas SAC305 loss in shear strength is eight times higher. After 2,000 cycles, HRL1 shear strength is 24% lower than its initial value, whereas the eutectic SnBi is 68.4% lower, and SAC305 is 81% lower (from its ini- tial value of 10.1 kgf). Summary Given the growing demand for high-reliability, low-temperature, lead-free solder alloys that can be reflowed below 200°C, the alloy characteristics—including melting behavior, microstructure, and ther- momechanical properties—need to be carefully considered. For the packages and experimental condi- tions discussed, the results shown here can be summarized as fol- lows: • HRL1 solder combines the higher tensile strength of SnBi alloys with yield strength and elongation similar to SAC305. • HRL1 solder enables peak reflow temperatures as low as 185–190°C for assembling BGA packages with Sn-Ag-Cu balls (i.e., hybrid solder joints), or 170–175°C for homogeneous HRL1 solder joints. • HRL1's drop shock and thermal cycling performance enables its use as a drop-in replacement for the test vehicles and experimental conditions shown here, and on a variety of other applications. Acknowledgments We thank our colleagues at the India R&D Centre for their key support for this work. We atively, extensive cracks are observed in SnBi and SAC305. For these testing conditions and compo- nents, all three alloys show a reduction in shear strength after thermal cycling (Figure 7), but HRL1 microstructure seems to withstand better the strains due to stress from thermal cycling. Figure 7: Effect of thermal cycling on shear strength. Figure 6: Cross-sections of (a) BGA84 solder joints after 1,500 thermal cycles and (b) chip resistors 1206 solder joints after 2,500 thermal cycles.