# Fabrication of a Conductive Pattern on a Photo-Polymerized Structure Using Direct Laser Sintering
## 4 Conclusions  
In this study, the possibility of forming a conductive circuit pattern through direct sintering was tested using a composite resin and a laser from PP-type 3D printing. Unlike previous similar studies, the goal was to develop a process that could directly form conductivity from a 3D surface without a separate chemical wet process in a single device.  
A composite resin was prepared by variously controlling the type of base resin, the type of metal powder, and the mixing ratio in order to derive the optimal result. Based on this, various laser process conditions were tested so that the polymer binder removal and selective sintering reaction could occur at the same time on the selected 50 vol% aluminum powder composite resin and the results were observed. Each result was evaluated by calculating the resistance value by measuring the IV curve through a potentiostat and analyzing the SEM image. Unlike the laser machining process, in which ablation is the main mechanism, when high-energy density was given by lowering the spot size, repetition rate, path interval, and scanning speed, only damage caused by excessive thermal energy occurred. On the other hand, when the energy density was excessively lowered, an intermetallic interconnection by the appropriate sintering reaction could not be formed, making it impossible to form the conductive pattern. Therefore, in this study, after the 3D printing of the 50 vol% aluminum composite resin, a 0.8 W UV laser was set to a beam spot size of 50 \(\upmu\)m and irradiated on the surface. At this time, when the pulse repetition rate, scan path interval, and scanning speed were set to 90 kHz, 10 \(\upmu\)m, and 50 mm/s, respectively, an optimal conductive pattern with a resistance of 0.33 \(\Omega\cdot\)cm\({}^{-1}\) was obtained. Furthermore, as shown in Figure 10, the feasibility of the sintered conductive pattern was confirmed by the construction and operation of LEDs using the circuit. The proposed process may contribute to the development of 3D-printed electronics and may enable a simple and inexpensive patterned circuit implementation.  
Figure 9: IV curves of the fabricated conductive pattern at various laser scanning speeds when the line width was 1.0 mm. The length of the pattern was 20 mm; the resistance per unit length is indicated in the upper left of the graph.  
**Author Contributions:** Conceptualization, M.-S.P.; methodology, M.-S.P.; software, M.-S.P.; validation, J.-H.J.; formal analysis, J.-H.J.; investigation, J.-H.J.; writing--original draft preparation, J.-H.J.; writing--review and editing, M.-S.P.; supervision, M.-S.P.; project administration, M.-S.P.; funding acquisition, M.-S.P. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study was supported by the Research Program funded by SeoulTech (Seoul National University of Science and Technology, U2022-0105).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.