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Microstructure-controlled stress evolution during Cu6Sn5 growth in Sn/Cu coatings

Jacobsson, Erik LU ; Hallberg, Håkan LU orcid ; Hektor, Johan LU and Ristinmaa, Matti LU orcid (2026) In Materialia 49.
Abstract

Growth of the intermetallic compound (IMC) Cu6Sn5 in Sn/Cu coatings is a major source of stress evolution and is closely linked to the reliability of electroplated Sn layers, including their susceptibility to whisker formation. Here, we investigate how Sn grain morphology and grain boundary (GB) transport control stress development during diffusion-controlled Cu6Sn5 growth. A thermodynamically consistent sharp-interface framework is developed that couples atomic diffusion, elasto-plastic deformation, moving interphase interfaces and GB diffusion and sliding. The model is solved in a finite element setting using the Voronoi implicit interface method to capture evolving... (More)

Growth of the intermetallic compound (IMC) Cu6Sn5 in Sn/Cu coatings is a major source of stress evolution and is closely linked to the reliability of electroplated Sn layers, including their susceptibility to whisker formation. Here, we investigate how Sn grain morphology and grain boundary (GB) transport control stress development during diffusion-controlled Cu6Sn5 growth. A thermodynamically consistent sharp-interface framework is developed that couples atomic diffusion, elasto-plastic deformation, moving interphase interfaces and GB diffusion and sliding. The model is solved in a finite element setting using the Voronoi implicit interface method to capture evolving Cu6Sn5 morphologies. Simulations of Sn coatings on Cu substrates reproduce experimentally observed trends in Cu6Sn5 growth and biaxial stress evolution. In columnar Sn microstructures, IMC growth produces a build-up of biaxial compressive stress that saturates at experimentally relevant levels, even without GB creep. In contrast, non-columnar microstructures activate GB diffusion and sliding along inclined boundaries, leading to substantial stress relaxation. The results show that GB diffusion and sliding are orientation-dependent relaxation mechanisms rather than sources of stress generation, providing a mechanistic explanation for the reduced stress levels observed in non-columnar Sn coatings.

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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Diffusion-controlled phase transformations, Grain boundary diffusion and sliding, Intermetallic compound, Plasticity, Voronoi implicit interface method
in
Materialia
volume
49
article number
102873
publisher
Elsevier
external identifiers
  • scopus:105048989483
ISSN
2589-1529
DOI
10.1016/j.mtla.2026.102873
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2026 The Authors.
id
1e6d298c-0913-45cd-9b57-23be2457ecb3
date added to LUP
2026-09-10 08:10:15
date last changed
2026-09-14 11:50:44
@article{1e6d298c-0913-45cd-9b57-23be2457ecb3,
  abstract     = {{<p>Growth of the intermetallic compound (IMC) Cu<sub>6</sub>Sn<sub>5</sub> in Sn/Cu coatings is a major source of stress evolution and is closely linked to the reliability of electroplated Sn layers, including their susceptibility to whisker formation. Here, we investigate how Sn grain morphology and grain boundary (GB) transport control stress development during diffusion-controlled Cu<sub>6</sub>Sn<sub>5</sub> growth. A thermodynamically consistent sharp-interface framework is developed that couples atomic diffusion, elasto-plastic deformation, moving interphase interfaces and GB diffusion and sliding. The model is solved in a finite element setting using the Voronoi implicit interface method to capture evolving Cu<sub>6</sub>Sn<sub>5</sub> morphologies. Simulations of Sn coatings on Cu substrates reproduce experimentally observed trends in Cu<sub>6</sub>Sn<sub>5</sub> growth and biaxial stress evolution. In columnar Sn microstructures, IMC growth produces a build-up of biaxial compressive stress that saturates at experimentally relevant levels, even without GB creep. In contrast, non-columnar microstructures activate GB diffusion and sliding along inclined boundaries, leading to substantial stress relaxation. The results show that GB diffusion and sliding are orientation-dependent relaxation mechanisms rather than sources of stress generation, providing a mechanistic explanation for the reduced stress levels observed in non-columnar Sn coatings.</p>}},
  author       = {{Jacobsson, Erik and Hallberg, Håkan and Hektor, Johan and Ristinmaa, Matti}},
  issn         = {{2589-1529}},
  keywords     = {{Diffusion-controlled phase transformations; Grain boundary diffusion and sliding; Intermetallic compound; Plasticity; Voronoi implicit interface method}},
  language     = {{eng}},
  publisher    = {{Elsevier}},
  series       = {{Materialia}},
  title        = {{Microstructure-controlled stress evolution during Cu6Sn5 growth in Sn/Cu coatings}},
  url          = {{http://dx.doi.org/10.1016/j.mtla.2026.102873}},
  doi          = {{10.1016/j.mtla.2026.102873}},
  volume       = {{49}},
  year         = {{2026}},
}