Small-Scale Strain in Tension Loaded Solder

Figure 1

A 1 mm x 0.8 mm area of interest on the dogbone sample allows for Eyy strain to be obtained throughout the solder line (82 microns thick).

The objective of this test was to determine the strain distribution within a solder line that was 82 microns thick. The specimen was a copper dogbone soldered together in the middle region. The dogbone width was 3.0 mm, but the field of view was zoomed into a small 1.0 mm region on the edge so that strains within that very thin solder line could be investigated. This region is indicated in Figure 1.

The sample was loaded in tension until failure, and images were taken at every 2 lbs of applied load. The VIC-3D Stereo Microscope system tracked the sub-pixel movements of the speckle pattern to measure surface displacements and strain data on the specimen. The full-field analysis was able to show how the strain was distributed throughout the solder.

During the test, 23 image pairs were analyzed so that strain development could be observed and analyzed. Figures 1 and 2 explore the y-axis strain (strain in the tensile loading direction) in the last image taken before failure. The contour plots may be displayed in 2D and overlaid on the deformed image (as seen in Figure 1) or displayed on a 3D plot (as seen in Figure 2).

Figure 2

Y-axis strain, εyy , at maximum loading

Figure 3

εyy , at maximum loading with user defined line

Data extraction tools are also available in VIC-3D. This enables the user to investigate global or user-defined local areas. Any number of the variables may be extracted into plots and tabular data.

Figure 3 displays a user-defined line within the solder region. Figure 4 shows the local strain along that user-defined line. The red line in Figure 4 reveals the strain along that user-defined line for the last image taken before failure, and the grey lines demonstrate how that strain is developed throughout the test. Loading data may be recorded through an analog signal and plotted against any of the available variables for global or user-defined local regions. Figure 5 shows the stress-strain graph for the average global strain.

Figure 4

εyy development within user defined line

Figure 5

Load vs. Global εyy