Investigation of Sn whisker growth in electroplated sn and Sn-Ag films as a function of plating variables and plastic deformation

Abstract

Sn whiskers have been extensively studied since 1950s. Consequently, many research have been reported for the growth mechanism of Sn whisker growth and the mitigation method for Sn whisker growth. However, the growth mechanisms of Sn whiskers are not yet fully understood. And more studies are still needed to establish mitigation strategies for the Sn whisker growth. In addition, addition of Pb neither became unable to use for the mitigation method of Sn whisker growth because use of Pb is restricted legally due to its harmful health effects and environmental concerns. To make matters worse, Sn whiskers were observed at automobiles involving rapid acceleration accidents. Therefore, it is urgent matters to establish mitigation strategies for the Sn whisker growth in Pb-free electronics, although many studies have been reported. Therefore, this study included three main objectives as followed: 1) Optimum mitigation method for Sn whisker growth on electroplated Sn-rich films using plating variables, storage conditions, and Ag addition. 2) Evaluation the behavior of deformation-induced Sn whisker growth on plastically deformed matte Sn films. And proposing the growth mechanism of deformation-induced Sn whisker growth. 3) Optimum mitigation method for deformation-induced Sn whisker growth on Sn-rich films used in connectors using storage conditions and Ag addition. Finally, optimum strategies for mitigation of Sn whisker growth are suggested in Pb-free electronics.

In Chapter 2, commercially available electroplated matte Sn, matte Sn-Ag, and bright Sn-Ag baths (of low-whisker formulations) are investigated to establish Sn whisker mitigation strategies for Sn-rich surface finishes. The effect of current density and plating thickness on Sn whisker growth is examined. And the effect of storage conditions are also investigated; ambient (30℃ , dry air) and high-temperature/high-humidity [55℃, 85% relative humidity (RH)] conditions. In addition, addition of Ag is investi...