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Scanning 3DXRD measurement of grain growth, stress, and formation of Cu6Sn5 around a tin whisker during heat treatment

Hektor, Johan LU ; Hall, Stephen A. LU ; Henningsson, N. Axel; Engqvist, Jonas LU ; Ristinmaa, Matti LU ; Lenrick, Filip LU and Wright, Jonathan P. (2019) In Materials 12(3).
Abstract

The 3D microstructure around a tin whisker, and its evolution during heat treatment were studied using scanning 3DXRD. The shape of each grain in the sample was reconstructed using a filtered-back-projection algorithm. The local lattice parameters and grain orientations could then be refined, using forward modelling of the diffraction data, with a spatial resolution of 250nm. It was found that the tin coating had a texture where grains were oriented such that their c-axes were predominantly parallel to the sample surface. Grains with other orientations were consumed by grain growth during the heat treatment. Most of the grain boundaries were found to have misorientations larger than 15°, and many coincidence site lattice (CSL) or other... (More)

The 3D microstructure around a tin whisker, and its evolution during heat treatment were studied using scanning 3DXRD. The shape of each grain in the sample was reconstructed using a filtered-back-projection algorithm. The local lattice parameters and grain orientations could then be refined, using forward modelling of the diffraction data, with a spatial resolution of 250nm. It was found that the tin coating had a texture where grains were oriented such that their c-axes were predominantly parallel to the sample surface. Grains with other orientations were consumed by grain growth during the heat treatment. Most of the grain boundaries were found to have misorientations larger than 15°, and many coincidence site lattice (CSL) or other types of low-energy grain boundaries were identified. None of the grains with CSL grain boundaries were consumed by grain growth. During the heat treatment, growth of preexisting Cu6Sn5 occurred; these grains were indexed as a hexagonal η phase, which is usually documented to be stable only at temperatures exceeding 186 °C. This indicates that the η phase can exist in a metastable state for long periods. The tin coating was found to be under compressive hydrostatic stress, with a negative gradient in hydrostatic stress extending outwards from the root of the whisker. Negative stress gradients are generally believed to play an essential role in providing the driving force for diffusion of material to the whisker root.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
CuSn, Scanning 3DXRD, Stress, Tin whiskers
in
Materials
volume
12
issue
3
publisher
MDPI AG
external identifiers
  • scopus:85060983809
ISSN
1996-1944
DOI
10.3390/ma12030446
language
English
LU publication?
yes
id
99b4a84b-04ec-4acc-a20b-f7738237325e
date added to LUP
2019-02-12 08:51:47
date last changed
2019-03-12 04:21:04
@article{99b4a84b-04ec-4acc-a20b-f7738237325e,
  abstract     = {<p>The 3D microstructure around a tin whisker, and its evolution during heat treatment were studied using scanning 3DXRD. The shape of each grain in the sample was reconstructed using a filtered-back-projection algorithm. The local lattice parameters and grain orientations could then be refined, using forward modelling of the diffraction data, with a spatial resolution of 250nm. It was found that the tin coating had a texture where grains were oriented such that their c-axes were predominantly parallel to the sample surface. Grains with other orientations were consumed by grain growth during the heat treatment. Most of the grain boundaries were found to have misorientations larger than 15°, and many coincidence site lattice (CSL) or other types of low-energy grain boundaries were identified. None of the grains with CSL grain boundaries were consumed by grain growth. During the heat treatment, growth of preexisting Cu<sub>6</sub>Sn<sub>5</sub> occurred; these grains were indexed as a hexagonal η phase, which is usually documented to be stable only at temperatures exceeding 186 °C. This indicates that the η phase can exist in a metastable state for long periods. The tin coating was found to be under compressive hydrostatic stress, with a negative gradient in hydrostatic stress extending outwards from the root of the whisker. Negative stress gradients are generally believed to play an essential role in providing the driving force for diffusion of material to the whisker root.</p>},
  articleno    = {446},
  author       = {Hektor, Johan and Hall, Stephen A. and Henningsson, N. Axel and Engqvist, Jonas and Ristinmaa, Matti and Lenrick, Filip and Wright, Jonathan P.},
  issn         = {1996-1944},
  keyword      = {CuSn,Scanning 3DXRD,Stress,Tin whiskers},
  language     = {eng},
  month        = {01},
  number       = {3},
  publisher    = {MDPI AG},
  series       = {Materials},
  title        = {Scanning 3DXRD measurement of grain growth, stress, and formation of Cu<sub>6</sub>Sn<sub>5</sub> around a tin whisker during heat treatment},
  url          = {http://dx.doi.org/10.3390/ma12030446},
  volume       = {12},
  year         = {2019},
}