Intermetallic compound growth suppression at high temperature in SAC solders with Zn addition on Cu and Ni-P substrates

The effect of adding 0.5-1.5 wt.% Zn to Sn-3.8Ag-0.7Cu (SAC) solder alloy during reflow and solid state ageing has been investigated. In particular, the role of the Zn addition in suppressing interfacial Intermetallic Compound (IMC) growth on Cu and Ni-P substrates has been determined. Solder-substrate couples were aged at 150 degrees C and 185 degrees C for 1000 h. In the case of 0.5-1.0 wt.% Zn on Cu substrate, Cu(3)Sn IMC was significantly suppressed and the morphology of Cu(6)Sn(5) grains was changed, leading to suppressed Cu(6)Sn(5) growth. In the SAC-1.5Zn/Cu substrate system a Cu(5)Zn(8) IMC layer nucleated at the interface followed by massive spalling of the layer into the solder, forming a barrier layer limiting Cu6Sn5 growth. On Ni-P substrates the (Cu,Ni)(6)Sn(5) IMC growth rate was suppressed, the lowest growth rate being found in the SAC-1.5Zn/Ni-P system. In all cases the added Zn segregated to the interfacial IMCs so that Cu(6)Sn(5) became (Cu,Zn)(6)Sn(5) and (Cu,Ni)(6)Sn(5) became (Ni,Cu,Zn)(6)Sn(5). The effect of Zn concentration on undercooling, wetting angles and IMC composition changes during ageing are also tabulated, and a method of incorporating Zn into the solder during reflow without compromising solder paste reflow described. (C) 2011 Elsevier B.V. All rights reserved.