Heat generated from Joule heating is an important factor in several failure mechanisms in microelectronic packaging (e.g. thermomigration, electromigration and etc) and large amount of the heat causes severe heat dissipation problem. It is further exaggerated by the continuous marching towards miniaturization of microelectronics. The techniques of measuring the Joule heating effects at the microscopic scale are quite limited especially for the full field measurement. Infrared microscopic imaging has been reported to measure the heat radiation by the Joule heating in the microscopic scale. Moire´ interferometry with phase shifting is a highly sensitive and a high resolution method to measure the in-plane full field strain. In this paper, it is demonstrated that the Joule heating effect can be measured by Moire´ interferometry with phase shifting at the microscopic scale. The copper sheet is used for the demonstration because of isotropic material property and well known thermal properties and parameters. The specimen was designed to minimize the out-of-plane strain and the strain caused by the thermal-structural effects. A finite element model was developed to verify the design of the structure of the specimen and the specimen was tested under different current density (input current from 0 to 24 A). Based on the research, a correlation relationship between the current density and the strain in two orthogonal directions (one in the direction of the current flow) was determined. The regression coefficients of the full field were analyzed. The experiment demonstrates the capability of measuring microscopic Joule heating effects by using Moire´ interferometry with phase shifting. The method can be further applied to the measurement of Joule heating effect in the microscopic solid structures in the electronic packaging devices.
Phase-shifting in achromatic moiré interferometry system
