Yasuhisa Fujimoto

Observation of Thermal Strain on Electronic Packages Using Digital Image Correlation

In this study, the thermal expansion of bi-metal specimen is measured by digital image correlation (DIC). A measurement system is developed for the evaluation of complex thermal strain distribution on electronic packages. A heating chamber is designed for applying the thermal load and DIC provides the full-field thermal deformation distribution of the bi-metal specimen due to temperature changes. The in-plane strain distribution measured by DIC is influenced by the out-of-plane displacement. By measuring the thermal expansion of the materials having known thermal expansion coefficient at same time, the effect of the out-of-plane displacement on the in-plane strain measurement is corrected. Experimental Results show that the thermal strain of the bi-metal specimen can be obtained by the measurement system including the out-of-plane displacement correction.

Thermal Strain Measurement Using Digital Image Correlation with Systematic Error Elimination

This research aims to develop a method for measuring small strains at minute area on an electronic packaging using digital image correlation. To this end, the systematic error in the measured displacement is corrected by using the relation between measured displacement and actual displacement. This relation is obtained by measuring rigid rotation and in-plane translation. The strain distribution with high spatial resolution can be obtained from the displacement distribution because the systematic error that affects the resolution of the strain is eliminated. This error elimination method is applied to the thermal strain measurement of a bimaterial which is composed of copper and steel. Results show that high spatial resolution strain distributions at minute area can be obtained by using this method.

Elimination of Periodical Error for Bi-directional Displacement in Digital Image Correlation Method

A technique for eliminating the periodical systematic error in bi-directional displacements by a digital image correlation method is investigated. The technique is based on a periodical error elimination method for single directional displacements which has been developed by the authors. In this technique, rotated and multiple translated images for the horizontal and the vertical directions are captured before a deformation. Translation amounts are determined from the rotation and the translated images. After the deformation, a single image is captured. The periodical error is eliminated using a calculation based on the translation amounts and the measured multiple displacements from the single deformed state image with the initial translated images. The elimination is applied to a thermal deformation measurement. As a result, periodical errors for bi-directional displacements can be eliminated. Therefore, it is expected that accurate in-plane displacements and strain components can be obtained using the proposed technique.