Effect of Bi and In on Microstructure Formation in Sn-3Ag-3Bi-3In/Cu and /Ni Solder Joints

Abstract:

Sn-3Ag-3Bi-3In solder has been investigated to improve the understanding of microstructure formation in this solder during solidification and soldering to Cu and Ni substrates. The as-solidified microstructures of Sn-3Ag-3Bi-3In samples were found to consist of a significant fraction of βSn dendrites with a complex eutectic between the dendrites. In total five phases were observed to form during solidification: βSn, Ag₃Sn, Bi, ζAg and a “Sn-In-Bi” ternary compound. Soldering of Sn-3Ag-3Bi-3In to substrates changed the phase equilibria in the system and caused the formation of additional phases: Cu₆Sn₅ during soldering to Cu and Ni₃Sn₄ and metastable NiSn₄ during soldering to Ni. It is shown that metastable NiSn₄ forms as a primary phase in a complex 5-component Sn-3Ag-3Bi-3In-Ni system. In and Bi were detected in solid solution in the βSn matrix in amounts of ~1.5-2at% and ~1.2at% respectively. Bi also existed as fine particles of two distinct types. (i): sub-micron (<500nm) coral-like particles and (ii) facetted particles measuring up to 7-8 μm.

• Periodical: Key Engineering Materials (Volume 700)
• Pages: 142-151
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.700.142
• Online since: July 2016
• Authors: Sergey A. Belyakov*, Christopher M. Gourlay
• Keywords: Intermetallic, Microstructure, NiSn₄, Pb-Free Soldering, Solidification

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