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Journal of Electronic Materials

, Volume 48, Issue 1, pp 17–24 | Cite as

Studying the Effect of Grain Size on Whisker Nucleation and Growth Kinetics Using Thermal Strain

  • Eric Chason
  • Fei Pei
  • Nupur Jain
  • Andrew Hitt
TMS2018 Microelectronic Packaging, Interconnect, and Pb-free Solder
  • 34 Downloads
Part of the following topical collections:
  1. TMS2018 Advanced Microelectronic Packaging, Emerging Interconnection Technology, and Pb-free Solder

Abstract

To understand how and why Sn whiskers nucleate, measurements were performed in which the thermal expansion mismatch was used to induce strain in the samples. The current work focuses on the effect of grain size by studying samples with a thickness of 8 μm to compare with previous studies on 2.5 μm samples. The stress evolution during cycles of heating is determined by monitoring the resulting curvature in the sample. At the same time, the number of whisker nuclei are measured with optical microscopy which enables the relationship between film stress and nucleation rate to be quantified, where the stress relaxation kinetics depend on the grain size. The rate of stress relaxation is greater in the thick samples than the thin samples for the same heating cycle and the final stress after relaxation is smaller for the thicker samples. The whisker volume evolution was determined by using short sequences of heating and then measuring the size of different features after each interval in the scanning electron microscope. This enabled quantification of the relationship between film stress and whisker growth rate. The growth rate depends on the stress above the final stress, similar to our previous results for the thinner samples. The whisker nucleation kinetics in the 8 μm samples can also be explained with the same model used for the 2.5 μm samples. However, the stress-dependent activation energy is shifted to lower values.

Keywords

Tin whiskers whiskering stress interconnects reliability stress relaxation thermal cycling creep 

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Notes

Acknowledgements

The authors gratefully acknowledge the support of the NSF-DMR under Contract DMR1501411 and technical input from Prof. Pradeep Guduru.

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Copyright information

© The Minerals, Metals & Materials Society 2018

Authors and Affiliations

  1. 1.School of EngineeringBrown UniversityProvidenceUSA
  2. 2.Amphenol-tcsNashuaUSA

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