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The resistivity of the sintered Cu thick film decreases with the weight percentage of the SiO2–ZnO–B2O3 additive in the mixing glass frits up to 50 wt%. As the weight percentage of the SiO2–ZnO–B2O3 additive in the mixing glass frits is over 50 wt%, the resistivity of the sintered Cu thick films is quite similar. The lowest resistivity (6.62 × 10−6 Ω‐cm) of the sintered Cu thick films occurs at 75 wt% of the SiO2–ZnO–B2O3 additive. Also, we observe the extensive glass phase framing around the large Cu grains in the Cu thick films sintered with low SiO2–ZnO–B2O3 additives (less than 50 wt%) narrows the cross‐section area of the electrical path. On the contrary, the round‐shaped glass phase solidified among the small Cu grains allows a larger cross‐section of the electrical path (a possible lower resistivity) for the Cu thick films sintered with higher SiO2–ZnO–B2O3 additives (larger than 50 wt%). The above results imply that the resistivity of the sintered Cu thick film correlates well with the microstructure (Cu grain size and the glass/Cu composite structure) of the sintered Cu thick films. Twin grain boundaries can clearly be observed in the sintered Cu thick films, especially for the Cu thick film sintered with the higher SiO2–ZnO–B2O3 additives. Owing to small Cu grains size and high density of Cu grain boundary, the probability of the grain boundaries with a high grain‐boundary energy in the Cu thick film sintered with high SiO2–ZnO–B2O3 additive would be much larger, comparing to that in the Cu thick film sintered with low SiO2–ZnO–B2O3 additive. Thus, more annealing twin boundaries formed in the Cu thick film sintered with high SiO2–ZnO–B2O3 additive. Hence, the formation of the twin boundary in the sintered Cu thick film helps reducing the resistivity of the sintered Cu films. [ABSTRACT FROM AUTHOR]

Tensile tests were carried on the electroplated Cu films with various densities of twin grain boundary. With TEM images and a selected area diffraction pattern, nano-twinned structure can be observed and defined in the electroplated Cu films. The density of the nano-twin grain structure can be manipulated with the concentration of gelatin in the Cu-sulfate electrolyte solution. We found that the strength of the Cu films is highly related to the twin-boundary density. The Cu film with a greater twin-boundary density has a larger fracture strength than the Cu film with a lesser twin-boundary density. After tensile tests, necking phenomenon (about 20 μm) occurred in the fractured Cu films. Moreover, by focused ion beam (FIB) cross-sectional analysis, the de-twinning can be observed in the region where necking begins. Thus, we believe that the de-twinning of the nano-twinned structure initiates the plastic deformation of the nano-twinned Cu films. Furthermore, with the analysis of the TEM images on the nano-twinned structure in the necking region of the fractured Cu films, the de-twinning mechanism attributes to two processes: (1) the ledge formation by the engagement of the dislocations with the twin boundaries and (2) the collapse of the ledges with the opposite twin-boundaries. In conclusion, the plastic deformation of nano-twinned Cu films is governed by the de-twinning of the nano-twinned structure. Moreover, the fracture strength of the nano-twinned Cu films is proportional to the twin-boundaries density. [ABSTRACT FROM AUTHOR]