Long term evolution of microstructure and stress around tin whiskers investigated using scanning Laue microdiffraction

Research output: Contribution to journalArticle

Standard

Harvard

APA

CBE

MLA

Vancouver

Author

RIS

TY - JOUR

T1 - Long term evolution of microstructure and stress around tin whiskers investigated using scanning Laue microdiffraction

AU - Hektor, Johan

AU - Micha, Jean Sébastien

AU - Hall, Stephen A.

AU - Iyengar, Srinivasan

AU - Ristinmaa, Matti

PY - 2019

Y1 - 2019

N2 - Scanning Laue microdiffraction was used to study the evolution of the microstructure and the stress field around two tin whiskers during ageing for up to 21 months. In the heterogeneous stress fields obtained, localised ridges of high compressive stress leading to the root of the whiskers were found. Due to the evolution of the intermetallic compound in the interface between the copper substrate and the tin coating, the stress field was also evolving with time. The temporal evolution of the stress field indicates that the regions supplying material to the whisker root is changing with time, highlighting that whisker growth is a highly dynamical process. During the experimental campaign, a new surface feature appeared in a grain boundary within the scanned area of the sample. The new feature had a twinning relationship with one of the neighbouring grains, a similar twin relation was also seen for one of the two larger whiskers. It is suggested that tin atoms diffuse out from the ridges of high compressive stress to the nearby, less compressed grain boundaries along which diffusion towards the root of the whisker occurs. The observations made from the Laue diffraction measurements also suggest that whiskers form in regions where the gradient in hydrostatic stress is large and that they grow to relax compressive stresses.

AB - Scanning Laue microdiffraction was used to study the evolution of the microstructure and the stress field around two tin whiskers during ageing for up to 21 months. In the heterogeneous stress fields obtained, localised ridges of high compressive stress leading to the root of the whiskers were found. Due to the evolution of the intermetallic compound in the interface between the copper substrate and the tin coating, the stress field was also evolving with time. The temporal evolution of the stress field indicates that the regions supplying material to the whisker root is changing with time, highlighting that whisker growth is a highly dynamical process. During the experimental campaign, a new surface feature appeared in a grain boundary within the scanned area of the sample. The new feature had a twinning relationship with one of the neighbouring grains, a similar twin relation was also seen for one of the two larger whiskers. It is suggested that tin atoms diffuse out from the ridges of high compressive stress to the nearby, less compressed grain boundaries along which diffusion towards the root of the whisker occurs. The observations made from the Laue diffraction measurements also suggest that whiskers form in regions where the gradient in hydrostatic stress is large and that they grow to relax compressive stresses.

KW - Lead-free solder

KW - Tin whiskers

KW - X-ray diffraction

U2 - 10.1016/j.actamat.2019.02.021

DO - 10.1016/j.actamat.2019.02.021

M3 - Article

VL - 168

SP - 210

EP - 221

JO - Acta Materialia

T2 - Acta Materialia

JF - Acta Materialia

SN - 1873-2453

ER -