Comparing the IMC layer growth in Sn-Cu, Sn-Ag-Cu and Sn-Ni-Cu layer systems

In this paper the intermetallic (IMC) layer growth mechanisms and rates are investigated in Sn-Cu, Sn-Ag-Cu and Sn-Ni-Cu layer systems. The aim of the study is to characterize the IMC layer growth in these layer structures and find relationship between their whiksering behaviors. On Cu base substrate, Ni or Ag for barrier layer and Sn for surface finish was electroplated. The samples were aged in elevated temperatures to induce intermetallic layer growth. Two kinds of aging conditions have been used: 50°C and 125°C. The IMC layer growth was checked by etching the samples with Focused Ion Beam (FIB) and observing the cross-sections with Scanning Ion Microscope (SIM) and Energy-Dispersive X-Ray Spectroscope (EDX). It will be shown that the barrier layers can effectively blocks the development of Cu₆Sn₅ IMC. It was observed that the IMC growth mechanisms are totally different in the Sn-Ag-Cu system than in the Sn-Cu and Sn-Ni-Cu systems. The growth characteristics of the Sn-Cu and Sn-Ni-Cu systems are similar, expect during the deposition of Sn layer which could be one main reason of the different tin whiskering abilities.