Journal of Electronic Materials

, Volume 41, Issue 3, pp 588–595 | Cite as

Stress Relaxation in Sn-Based Films: Effects of Pb Alloying, Grain Size, and Microstructure

  • Nitin Jadhav
  • Jacob Wasserman
  • Fei Pei
  • Eric Chason
Article
First Online:
Received:
Accepted:

Abstract

Stress is believed to provide the driving force for growth of Sn whiskers, so stress relaxation in the Sn layer plays a key role in their formation. To understand and enhance stress relaxation in Sn-based films, the effects of Pb alloying and microstructure on their mechanical properties have been studied by observing the relaxation of thermal expansion-induced strain. The relaxation rate is found to increase with film thickness and grain size in pure Sn films, and it depends on the microstructure in Pb-alloyed Sn films. Measurements of multilayered structures (Sn on Pb-Sn and Pb-Sn on Sn) show that changing the surface layer alone is not sufficient to enhance the relaxation, indicating that the Pb enhances relaxation in the bulk of the film and not by surface modification. Implications of our results for whisker mitigation strategies are discussed.

Keywords

Sn whisker packaging tin whisker thermal expansion-induced strain Pb-free solder thermal stress surface modification 
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Copyright information

© TMS 2011

Authors and Affiliations

  • Nitin Jadhav
    • 1
  • Jacob Wasserman
    • 1
  • Fei Pei
    • 1
  • Eric Chason
    • 1
  1. 1.School of EngineeringBrown UniversityProvidenceUSA

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