Effect of mixing glass frits on electrical property and microstructure of sintered Cu conductive thick film

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.