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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.49  No.2 (2008)  >  pp.376-381

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Synthesis of the Combination Solder of 80Au-20Sn/42Sn-58Bi and Thermodynamic Interpretation of the Microstructural Evolution

Chang Joon Yang1), Moon Gi Cho1) and Hyuck Mo Lee1)
1) Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology

A Pb-free combination solder structure was successfully attained from a high-melting 80Au-20Sn solder alloy completely wrapped in a low-melting 42Sn-58Bi solder paste (the numbers of which are all in mass% unless specified). The phases of (Au,Ni)3Sn4 and AuSn4 were observed at the interface between Sn-Bi solder and Cu/Ni/Au UBM, whereas the (Au,Ni)3Sn2 phase was observed at the interface between Au-Sn solder and Cu/Ni/Au UBM. The interfacial reaction between the Au-Sn solder and the Sn-Bi solder resulted in the formation of AuSn2 on the side of the Sn-Bi solder and AuSn on the side of the Au-Sn solder. All of these interfacial reactions were explained with relevant equilibrium phase diagrams. Moreover, we found that there is a limit in the optimum solder volume for a well-defined combination solder structure that can be applied to organic substrates with an increased remelting temperature.

combination solder structure, tin-bismuth, gold-tin, step soldering, phase equilibria

Received: August 08, 2007
Accepted: November 27, 2007 , Published online: January 25, 2008
Copyright (c) 2008 The Japan Institute of Metals



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