Interfacial reactions between molten Sn-Bi-X solders and Cu substrates for liquid solder interconnects

This paper reports on the interfacial reaction kinetics between molten Sn-58Bi solder and Cu substrates for extended temporal scales. Also studied are the effects of a series of elemental additions of 1-2 wt.% Al, Cr, Cu, Si, Zn, Ag, An, Pt and Nb into the basic Sn-5813i solder, in an attempt to produce a barrier layer that slows down intermetallic compound (IMC) growth. At temperatures between 200 and 240 degrees C, grain boundary-/molten channel-controlled growth of eta-phase (Cu6Sn5), followed by diffusion-controlled simultaneous growth of the epsilon-phase (Cu3Sn) and eta-phase (Cu6Sn5), between the molten Sn-5813i solder and the Cu substrate was observed, and a layer of 6 mu m Cu could survive for approximately 24-48 h. Addition of 1 wt.% Zn resulted in a layer of gamma-Cu5Zn8, instead of Cu3Sn and Cu6Sn5, forming at the interface, leading to an increase in the lifetime of the Cu substrate to greater than 120 h at 200 degrees C, while the other additions failed to slow down IMC formation. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.