8 Speckling and Testing with DIC at Microscales 71 Fig. 8.6 Aluminum painted white with carbon powder deposited, 1.2 mm by 1.0 mm field of view Fig. 8.7 Relative X displacement of second-level interconnect at 170 ◦C 8.4 DIC Results Early results illustrated that DIC could track the movement of non-homogeneous structures. Figure 8.7 shows the displacement field of a second-level interconnect in a microprocessor along with a slight distortion in the strain field of the substrate where the material is not uniform. Trying to validate the test measurements proved more difficult. For validation, DIC was used to measure the thermal expansion of a simple aluminum specimen. Test results were fairly accurate at measuring the expansion of the aluminum, but noise was a significant problem. The noise in the system was higher than the strain signal until the temperature of the specimen was above 70◦C. Even at the maximum applied temperature, 170◦C, the noise was still equal to about one quarter of the total signal. The noise seen in tests also increased with temperature. By taking a quick sequence of images at temperature, there was no evidence of temporal variations in the images. Changes in the stain over a short time could be associated with diffraction
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