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

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Abstract

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, Cu3Sn IMC was significantly suppressed and the morphology of Cu6Sn5 grains was changed, leading to suppressed Cu6Sn5 growth. In the SAC-1.5Zn/Cu substrate system a Cu5Zn8 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 Cu6Sn5 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.

Original languageEnglish
Pages (from-to)176-188
Number of pages13
JournalJOURNAL OF ALLOYS AND COMPOUNDS
Volume511
Issue number1
DOIs
Publication statusPublished - 15 Jan 2012

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