Combinatorial Studies for the Minimization of Tin Whiskers Growth in Lead Free Electronics

A combinatorial materials science method for screening potential elemental additions to mitigate tin whisker formation on Pb-free electronics is presented. This combinatorial method is demonstrated using compositional gradient libraries deposited on glass substrates. Fabrication and heat treatment of combinatorial libraries is discussed. The effectiveness of this high-throughput screening method becomes evident from the analysis of two ternary systems (W-Cr-Ni and Mo-Al-Co) deposited over a tin matrix on glass substrates. Scanning electron microscopy revealed that tin whiskers tend to nucleate and grow on samples with no compressive stresses associated with the formation of intermetallic layers. Additionally, a nickel layer between the glass and tin was found to hinder the formation of whiskers; however, the traditional argument of Ni as a diffusion barrier between Sn-Cu not longer explains the observed behavior. This combinatorial method provides a rapid assessment tool to identify potential elemental mixtures to mitigate tin whiskers while using a simple, cost effective experimental approach.Copyright © 2009 by ASME