Cyclic Stress Measurement Method Using Grain Size of Grown Grains in Electrodeposited Copper Foil

Abstract

The copper electroplating stress measurement method uses the grain growth in copper foil. The grain growth is a kind of thermal recrystallization that is affected by the magnitude of prestraining. Since a lot of grain nucleation occurs at the large prestraining, the large shearing stress should also lead to the same effect. On the basis of the above, we investigate the stress dependence of the grown grain size. We confirmed that the size of grown grains is expressed by the three-parameter Weibull distribution, and the relationship between scale parameter g and arithmetic mean of grain size d^* has a linear relationship until the grain growth rate r^* reaches 50%. It is also recognized that the mean grown grain size becomes smaller with increasing shearing stress amplitude. To measure the shearing stress amplitude, the relationship between mean grain size, shearing stress amplitude, and the number of cycles is experimentally formulated. Moreover, even if the number of cycles is unknown, measuring both r^* and d^* enables us to estimate the shearing stress amplitude.