Authors: Fei Pei Allan F Bower Eric Chason
Publish Date: 2015/08/28
Volume: 45, Issue: 1, Pages: 21-29
Abstract
Whiskers and hillocks that grow out of Snbased coatings are a critical reliability issue in Pbfree electronics Although their growth is widely regarded as a stressrelaxation mechanism quantitative understanding of the relationship between the stress growth kinetics and strain relaxation is still lacking In this work the wellcontrolled strain induced by thermalexpansion mismatch was used to study the whiskering behavior of electroplated Sn films Stress was quantified by monitoring wafercurvature and the density of whiskers and hillocks was measured simultaneously by use of optical microscopy Evolution of the volume of individual features was also measured by scanning electron microscopy after different periods of heating The measurements were used to develop a model for temperaturedependent and stressdependent growth kinetics of whiskers and hillocks and to determine the amount of strain relaxation which occurs as a result of their formation
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