Aging Characteristics of Sn-Ag Eutectic Solder Alloy with the Addition of Cu, In, and Mn
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EUTECTIC Sn-3.5Ag solder has received attention globally as a promising alternate to conventional eutectic Sn-Pb solder owing to its nontoxic nature, per wettability and mechanical properties with the former. Two major aspects for accepting a commercial solder alloy are the melting point of the system and the ability of providing substantial mechanical support to the components, apart from electrical conductivity.[1] The addition of alloying elements such as Cu, In, Ni, Co, Bi, and Sb to Sn-Ag solder alloy is one of the feasible solutions to combat the requirements. A small amount of Cu addition decreases the melting point of Sn-Ag solder and improves wettability.[2] The Ni along with Cu promotes the formation of additional intermetallic phase to enhance the bond strength.[1] Similarly, indium is responsible for lowering the melting point and increment in wettability of the Sn-Ag solder.[3] The Co raises the capability to retain adequate shear strength even after aging and depresses the reaction Cu6Sn5 + Cu fi Cu3Sn.[4] Both shear strength and tensile strength of the Sn-Ag alloy improve with the addition of Sb and Bi.[5,6] It has been explored that when the Sn-Ag alloy with or without the addition of minor elements is soldered M. GHOSH, S.K. DAS, and A.K. RAY, Scientists, are with the Materials Science and Technology Division, National Metallurgical Laboratory (CSIR), Jamshedpur-831007, India. Contact e-mail: [email protected] ABHIJIT KAR, Postdoctoral Researcher, formerly with the School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, South Korea440746, is with the Laboratory for Joining and Interface Technology, EMPA-Swiss Federal Laboratories for Materials Testing and Research, Du¨bendorf, CH: 8600, Switzerland. Manuscript submitted March 12, 2009. Article published online August 19, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
with copper substrate, the microstructure of the assembly in the reaction zone consists of Cu-Sn intermetallic compound (IMC).[2,4] Under service exploitation, the morphology of the intermetallics changes according to the thermal process history. The time-dependent structural change is a critical factor in determining the performance of interconnections in electronics.[7] With respect to substrate, both the solder alloy and the intermetallics have different thermal properties and eventually cause failures to solder joints after prolonged service exposure. With the advent of new generation lead-free solder alloys, which in general have higher melting points than that of the conventional Sn-37Pb solder, designers are interested in the comparative performance of different lead-free alloys and the efficiency of the life prediction method. Since the homologous temperature exceeds 0.5 at the operating temperature for most solder alloys, thermally activated structural and mechanical property changes play an important role in evaluating their reliability in service. Xiao et al. have explored that, at room temperature, Sn-Ag-Cu is age softened owing to the gro
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