Biaxial Stress Measurement Using Electrodeposited Copper Foil : Method to Judge the Sign of Biaxial Stress Ratio Using Grain Growth Direction

Abstract

Copper electroplating stress measurement method uses the grain growth in copper foil. This method can detect the maximum shearing stress by measuring the grown grain density. However, it's necessary to judge the sign of biaxial stress ratio (=σ_2/σ_1) beforehand in order to detect the principal stress. In this report, it pays attention to the grain growth direction to judge the sign of biaxial stress ratio, since it can be expected that the grain growth direction differs with the sign of biaxial stress ratio. The grain growth direction is investigated by the image processing software after carrying out the cyclic loading test under the various biaxial stress ratios which include positive and negative values. It's clear that the maximum values of relative frequency of grain growth direction occur periodically when biaxial stress ratio is negative. On the other hand, such periodicity is not observed when biaxial stress ratio is positive. Moreover, the grain growth rate is also different in the sign of biaxial stress ratio. These results can be explained by considering the direction of maximum shearing stress.