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. 2018 Nov 9;11(11):2229.
doi: 10.3390/ma11112229.

Imaging the Polymorphic Transformation in a Single Cu₆Sn₅ Grain in a Solder Joint

Flora Somidin  1   2 , Hiroshi Maeno  3 , Xuan Quy Tran  4 , Stuart D McDonald  5 , Mohd Arif Anuar Mohd Salleh  6 , Syo Matsumura  7   8 , Kazuhiro Nogita  9
Affiliations

Imaging the Polymorphic Transformation in a Single Cu₆Sn₅ Grain in a Solder Joint

Flora Somidin et al. Materials (Basel). .

Abstract

In-situ observations of the polymorphic transformation in a single targeted Cu₆Sn₅ grain constrained between Sn-0.7 wt % Cu solder and Cu-Cu₃Sn phases and the associated structural evolution during a solid-state thermal cycle were achieved via a high-voltage transmission electron microscope (HV-TEM) technique. Here, we show that the monoclinic η'-Cu₆Sn₅ superlattice reflections appear in the hexagonal η-Cu₆Sn₅ diffraction pattern upon cooling to isothermal 140 °C from 210 °C. The in-situ real space imaging shows that the η'-Cu₆Sn₅ contrast pattern is initiated at the grain boundary. This method demonstrates a new approach for further understanding the polymorphic transformation behavior on a real solder joint.

Keywords: Cu6Sn5 intermetallic compound; electron diffraction; high-voltage transmission electron microscopy; polymorphic phase transformation; time-temperature transformation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
FIB lamella sample. (a) Backscattered SEM image; (b) high and (c) low magnification bright-field plasmon-filtered TEM images; (d) SADP of the fresh selected Cu6Sn5 grain at room temperature before the in-situ heating experiment.
Figure 2
Figure 2
Simulated electron diffraction patterns of the (a) monoclinic η′-Cu6Sn5 C12/c1 structure and (b) hexagonal η-Cu6Sn5 P63/mmc structure corresponding to the obtained SADPs in this study.
Figure 3
Figure 3
(A) Corresponding SADPs in the observed Cu6Sn5 grain from time point-a to -i in the (B) profile temperature of the in-situ HV-TEM observations in diffraction mode.
Figure 4
Figure 4
Series of SADPs in this study tilted to the on-axis {330}H (={060}M) Kikuchi band.
Figure 5
Figure 5
(a,c,e) bright-field plasmon-filtered TEM images corresponding to captured SADPs in (b,d,f); (g) Temperature profile of the in-situ HV-TEM observations; (h) selected still-frame TEM images from in-situ video taken at time points 1 to 6 in the temperature profile showing the observation analysis. Video of the in-situ cooling observation can be seen in Supplementary Video S1.
Figure 6
Figure 6
The monoclinic and hexagonal structures simulated by Single Crystal software showing the (020)M and (110)H planes, respectively.
Figure 7
Figure 7
The morphology evolution of sample. (a–d) Low magnification bright-field plasmon-filtered TEM images; (e) secondary and (f,g) backscattered SEM images of the lamella sample after the in-situ experiment; (g) analysis of post-thinned FIB lamella sample.
See this image and copyright information in PMC

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