Achieving High Reliability Low-Cost Lead-Free SAC Solder Joints via Mn Doping
By Dr. Ning-Cheng Lee, Dr. Weiping Liu, Ronald C.Lasky, PhD, PE, and Timothy Jensen
Oct 24, 2013
In this study, the reliability of low Ag SAC alloy doped with Mn (SACM) was evaluated under JEDEC drop, dynamic bending, thermal cycling, and cyclic bending test conditions and compared to eutectic SnPb, SAC105, and SAC305 alloys. SACM is a patent pending alloy consisting of 0.5-1% Ag, 0.5-1% Cu, <0.1% Mn. SACM alloy achieved a higher drop test and dynamic bending test reliability than SAC105 and SAC305, and exceeded SnPb for many test conditions. More significantly, SACM matched SAC305 in thermal cycling performance.
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In other words, the low cost SACM achieved a better drop test performance than the low Ag SAC alloys, plus the desired thermal cycling reliability of high Ag SAC alloys. The mechanism for high drop shock performance and high thermal cycling reliability can be attributed to a stabilized microstructure, with uniform distribution of fine IMC particles, presumably through the inclusion of Mn in the IMC. The cyclic bending results showed SAC305 to be the best and all lead-free alloys were equal or superior to SnPb. The reliability test results also showed that NiAu is a preferred surface finish for BGA packages over OSP.
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