Authored By:
Jie Geng, Ph.D., Harris Jilani, and Hongwen Zhang, Ph.D.
Indium Corporation
NY, USA
Summary
A novel lead-free solder paste, Durafuse® HR (DFHR), has been developed using Durafuse® technology. This technology demonstrates the combined merits of each constituent solder powder in the paste. DFHR is based on Sn-Ag-Cu alloy system and contains bismuth (Bi), indium (In), and antimony (Sb). The paste melting temperature ranges from 205–221°C and can be processed with traditional 96.5Sn3Ag0.5Cu (SAC305) reflow profiles. Voiding performance was evaluated using Quad Flat No-Lead (QFN) components with OSP and ImSn surface finishes. The area percentage of voids for the thermal pad was less than 15%, being much lower than in SAC305.
Thermal fatigue behavior was investigated under two thermal cycling profiles: 1) -40 to 125°C, and 2) -40 to 150°C. Both profiles have a 10-minute dwell time at each extreme temperature. Thermal cycling tests were carried out using various components on daisy-chained test boards, including CABGA192, QFN (MLF68) and chip resistors (0603 and 1206). The degradation of solder alloys caused by thermal fatigue was evaluated with shear test and cross section investigation. DFHR voiding performance and thermal fatigue resistance improved dramatically compared to SAC305 and other high-reliability solder pastes.
Conclusions
A novel lead-free solder paste, Durafuse® HR (DFHR), has been developed using Durafuse® technology, i.e. mixing solder powder technology. DFHR is based on Sn-Ag-Cu alloy system and contains bismuth (Bi), indium (In), and antimony (Sb). The paste melting temperature ranges from 205–221°C and can be processed with traditional SAC305 reflow profiles. The area percentage of voids for the thermal pad of Quad Flat No-Lead (QFN) was less than 15%, being much lower than in SAC305 and SACBSbN. The joints formed with DFHR show improved thermal stability for chip resistors, CABGA192 and QFN than SAC305 and SACBSbN under TCTs -40/125°C and -40/150°C. In summary, both low-voiding and high thermal reliability could be achieved with Durafuse® HR lead-free solder paste.
Initially Published in the SMTA Proceedings
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