Time- and temperature-dependent wetting behavior of eutectic SnPb on Cu leadframes plated with Pd/Ni and Au/Pd/Ni thin films

P. G. Kim*, King-Ning Tu, D. C. Abbott

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

We have studied the wetting behaviors of eutectic SnPb solder on Cu leadframes plated with Pd/Ni and Au/Pd/Ni thin films. For the Pd/Ni, we used two thicknesses of Pd of 760 and 2500 Å to study the thicknesses effect. For the Au/Pd/Ni, we used either immersion Au (50 Å) or acid Au (50 Å) flashed on 1000 Å Pd to study the effect and method of adding Au to the Pd surface. In addition, we investigated the wetting on a PdSn3 compound surface made by plating Sn or eutectic SnPb on Pd/Ni samples and then stripping the Sn or SnPb layer off. In all these samples, we found the wetting behavior to be time and temperature dependent. No stable wetting angles could be observed; the diameter of the solder caps increased with wetting time. Yet rather surprisingly, the diameter decreased with increasing wetting temperature from 200 °C to 240 °C. The largest cap diameter was observed at the lower temperature of 200 °C for Pd/Ni and stripped Pd/Ni, but at the intermediate temperature of 220 °C for Au/Pd/Ni. The smallest cap diameter was obtained at the higher temperature of 240 °C for all substrates. In examining the interfaces, we found the reaction products to be a ternary Pd-Ni-Sn compound and Ni3Sn4 for all substrates. The ternary compound grains were broken off from the interface, and scattered into the molten solder as soon as the Ni3Sn4 was formed. The latter forms a rather uniform layer consisting of small scallop-type grains on the unreacted Ni. We found that the growth rate of Ni3Sn4 is much slower, by a factor of about 10, than that of Cu6Sn5 in the reaction between Cu and eutectic SnPb.

Original languageEnglish
Pages (from-to)770-775
Number of pages6
JournalJournal of Applied Physics
Volume84
Issue number2
DOIs
StatePublished - 15 Jul 1998

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