## 3 Results and Discussion
### Vertical Line  
#### 3.2.1 Effect of Patterning Space  
In the previous horizontal line test, when the feed rate was increased, even though the average laser power was increased together, time and energy for the chemical reduction reaction were insufficient, indicating that the desired metal deposition was impossible. In addition, when the number of lines was increased to activate the reduction reaction, unintended ablation of the thin copper layer occurred in the overlapping region, making it difficult to obtain a stable conductive structure. Therefore, focusing on the fact that deposition was well performed on one edge where the laser was not directly overlapped according to the direction of the scan path, a vertical line shape scan path was used, as shown in Figure 4a. In this case, if the laser scan proceeded from left to right, the copper deposited on the right edge of the vertical line would continue to ablate, but the copper deposited on the left edge would continue to accumulate and be densely deposited. Accordingly, it was expected that a completed conductive line could be obtained if the vertical line scan was continuously performed. At this time, the length of the patterning width A, which determines the line width of the finally formed conductive line, was fixed to 50 \(\upmu\)m, similar to the laser beam diameter. This made it possible to form a conductive line with a width of 100-200 \(\upmu\)m similar to the previous studies. The process results were observed while reducing the size of patterning space B, which affected the processing speed and energy density per unit area by every half from 100 \(\upmu\)m.  
As shown in Figure 4b, when the length of B was 100 \(\upmu\)m, traces of deposition by the copper reduction were observed, but sufficient reduction reactions did not occur stably. On the other hand, it could be seen that when the length of B was reduced, the thermal energy by the laser increased. Thus, the formation of the deposited structure by the reduction reaction was significantly improved. When B was 25 \(\upmu\)m, the deposited structure with the connected line shape could be obtained, but the conductivity was very unstable. As shown in Figure 4d, there was a section in which unstable deposition occurred due to the excessive gap between the laser pattern and the pattern.  
Figure 3: Horizontal scan result according to number of lines: (**a**) schematic diagram; (**b**) single line; (**c**) 3 lines; (**d**) 5 lines.  
On the other hand, when B was reduced to 12.5 \(\upmu\)m or less, a completely connected conductive deposition line structure could be obtained. When B was reduced to 6 \(\upmu\)m, a denser deposited structure could be obtained, but it could be seen that the line width was irregularly formed due to excessive energy. Therefore, in this study, patterning space B was selected as 12.5 \(\upmu\)m. The deposited line width was 185 \(\upmu\)m, and the laser patterning time required to fabricate a 10 mm long conductive line was about 80 s. Compared to previous studies, when converted to the horizontal feed rate of one straight line, it was about 0.124 mm/s. It was found that both the energy used and the process speed increased by about 10 times compared to the previous studies.