Authored By:
Jie Geng, Ph.D. and Hongwen Zhang, Ph.D.
Indium Corporation
NY, USA
Summary
Since antimony (Sb) has the potential to improve the thermal fatigue resistance of solder joints in harsh conditions, the degree of such improvement in reliability depends on the alloying content of Sb, which is usually in the range of 1.5 to 9 wt.%. In this work, thermal performance of five Sn/3.2Ag/0.7Cu/xSb (x is in the range of 4.5 to 6.5 wt.%) alloys were compared to select the optimized Sb content. When shear testing was conducted at 25, 75, and 150℃, 90.6Sn/3.2Ag/0.7Cu/5.5Sb (Indalloy®276) showed the best performance at those temperatures.
The shear test done for the 0805 chip resistors at intervals of TCT -40 to 125℃ also confirmed that 5.5 wt.% of Sb promoted the best shear strength during thermal cycling. Thus, 90.6Sn/3.2Ag/0.7Cu/5.5Sb was identified and developed for testing in targeting high reliability with a wide service temperature capability.
90.6Sn/3.2Ag/0.7Cu/5.5Sb has a melting temperature range of 223–232℃ and could be processed with traditional SAC305 reflow profiles. The thermal fatigue behavior was investigated under a thermal cycling profile of -40 to 125℃ with 10 minutes dwell time at each extreme temperature. The thermal cycling tests were carried out using various components on daisy-chained test boards, such as CABGA192 and chip resistors (including 0805 and 0603). The degradation of solder alloys caused by thermal fatigue was evaluated with shear testing, in-situ electrical continuity monitoring, dye penetrant (Dye & Pry), and cross section investigation. Alloying with 5.5 wt% of Sb dramatically improved the thermal fatigue resistance compared to SAC305.
Conclusions
Thermal performance of five Sn/3.2Ag/0.7Cu/xSb (x in range of 4.5 to 6.5 wt.%) alloys were compared to select the optimized Sb content. Based on shear testing at various temperatures and at different intervals of TCT -40 to 125℃, 90.6Sn/3.2Ag/0.7Cu/5.5Sb (IND276) showed the best performance in those Sb-containing alloys. Thus, this composition with the addition of 5.5 wt.% of Sb was identified and developed for testing in targeting high reliability with a wide service temperature capability. IND276 has a melting temperature range from 223–232℃ and could be processed with traditional SAC305 reflow profiles. The crack resistance of IND276 in the components of CABGA192 and chip resistors are better than SAC305 under thermal cycling of -40 to 125℃. Alloying with 5.5 wt% of Sb dramatically improved the thermal fatigue resistance compared to SAC305.
Initially Published in the SMTA Proceedings
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