In the semiconductor device field, the element materials constituting the interior of the semiconductor devices are rapidly miniaturized due to continuous improvement of high performance and power saving. However, it's getting harder to guarantee the long-term reliability of products because of the various degradation phenomena such as very high local Joule heating and electromigration (EM). Recently, it is reported that EM tends to occur along the grain boundaries in the interconnection material, and thus, it is necessary to quantitatively evaluate the grain boundary strength for estimating the lifetime of the interconnection and clarification of the dominant factors in order to assure the product reliability. In this study, grain boundary quality in terms of order of atomic arrangement was evaluated by using the analysis parameter IQ (Image Quality) value obtained from electron back-scatter diffraction (EBSD) method, and grain boundary strength was evaluated quantitatively by applying micro tensile test method to electroplated copper thin films used as an interconnection material. As a result, it was found that the strength of both a grain and a grain boundary changed as a function of the order of the atomic arrangement. In the low IQ value range, brittle fracture occurred at a grain boundary, and the strength of a grain boundary monotonically decreased as the IQ value decreased. On the other hand, in the high IQ value range, transgranular ductile fracture appeared and the yield stress of a grain monotonically decreased as the IQ value increased. Therefore, the IQ values was found to be the dominant factor of the strength of a grain and a grain boundary.