Effect of Environmental Conditions on Tin (Sn) Whisker Growth

Heshmat A Aglan,Kaushal R Prayakarao,David V Burdick,Md Karim Rahman

doi:10.4236/eng.2015.712071

Abstract

This research focuses on tin whisker growth under two different environmental conditions namely hygrothermal and a salt solution. Tin coated brass coupons were used for this study to analyze the growth of tin whiskers over time. Their growth rates were examined periodically using optical and scanning electron microscopy. The physical characteristics of the tin whiskers were identified for each environmental condition. It was discovered that submersion of tin coated brass substrates in 5% salt solution considerably increased the density (number of whiskers per unit area), and the length of the whiskers. In addition, it was found that the geometry and aspect ratio of tin whiskers were different for each environment.

Highlights

Tin whisker growth is a challenging problem facing the Aerospace, Defense and High Performance Electronics industry
A scratched flat tin coated brass coupon submerged in 5% NaCl solution after 5700 hours was taken for scanning electron microscopy (SEM) analysis on the suspected locations
The scratched flat coupon from the hygrothermal environment had numerous hillocks made of pure tin after 5700 hours of exposure

Summary

Introduction

Tin whisker growth is a challenging problem facing the Aerospace, Defense and High Performance Electronics industry. Lee and Lee noted that Bardeen-Herring dislocation transports the tin atoms to the crack until the stress is relieved It has recently reported [19] that the mysterious driving force behind tin whisker is the strain gradient. Another theory proposed by Galyon and Palmer [22], named as “Integrated Theory on Whisker Formation and Growth” described that a vacant zone is created within the brass substrate, named the Kirkendall zone, close to the tin film and brass substrate interface due to the dominant diffusion of brass into tin [22] This Kirkendall zone forms shrinkage because of the vacancy, and the shrinkage effects to a state of tensile stress in that zone. The physical characteristics of tin whiskers, density and length were identified for each environmental condition

Materials and Experimental

Optical Microscope Observations

Conclusion