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A Comparison Study of SAC405 vs. SAC387 Lead-Free Solder Ball Alloy
Keywords: Sn-Ag-Cu Alloy, Solder Joint Reliability, Intermetallic
In this study, two Sn-Ag-Cu alloys, namely SAC405 & SAC387 were compared in terms of the following characteristics: alloy properties, solder ball surface morphology, solder ball surface cleanliness through Auger elemental depth profile analysis, cold ball pull (CBP) and ball shear strength (at time zero, after test, after multiple reflow, after high temperature storage, and after moisture sensitivity level 3/2600C), IMC morphology and thickness, and missing ball after functional testing. The results showed that SAC387 has higher tensile strength for better thermal fatigue performance. In terms of surface morphology, SAC405 was found to have coarser dendrites on the ball surface that form notches and channels which may trap contamination and prevent the dispense of flux. The finer dendrites on the SAC387 ball surface prevent contamination and flux entrapment, thus prevent voids in the IMC and provides better mechanical strength. Auger elemental depth profile analysis showed higher carbon level on SAC405 as well as the presence of phosphorus. This may affect IMC formation and affect solder joint performance. With SAC387, lower carbon level and no phosphorus is found on the surface of the ball. The sharp cliff in the profile of SAC387 suggests that the surface of the solder ball was smoother. In term of CBP and ball shear tests, SAC387 had shown lower CBP brittle failure rate and significantly higher CBP strength and ball shear strength and ball shear Cpk at all the read points. In terms of IMC morphology and thickness, SAC387 has lower IMC growth than SAC405 in most of the read points. In terms of missing ball after functional testing, characterization result with ~130units test sample size showed that SAC405 has 0.78% missing ball yield loss at final test whereas SAC387 has zero yield loss. In conclusion, SAC387 solder alloy provides more reliable lead-free solder joint than SAC405.
Eu Poh Leng, Senior Staff Engineer (Research & Development Engineer III)
Freescale Semiconductors Malaysia Sdn Bhd
Petaling Jaya, Selangor 47300,
Malaysia


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