# Fabrication of a Conductive Pattern on a Photo-Polymerized Structure Using Direct Laser Sintering
## 2 Materials and Methods
### Experimental Conditions  
The PP-type 3D printer used can build structures of dimensions up to 50 mm \(\times\) 50 mm \(\times\) 200 mm. The main components were the blade, Z-stage, and controller. In the case of the composite resin, as the viscosity was relatively high, a flattening process was performed to a desired thickness using a blade after supplying the material. The laser used for the photo-polymerization and selective metal sintering was a 3 W pulsed UV laser with a wavelength of 355 nm. However, as the maximum power was limited according to the pulse repetition rate used, the experiment was conducted whilst the average power was fixed at 0.8 W, which could be stably irradiated. The results were observed by changing the various process parameters that could control the reaction time and the irradiated energy density that could affect the selective local laser sintering. In each experiment, each process variable was changed based on the reference condition shown in Table 3. In order to compare and evaluate the experimental results for each process variable, the pattern shape was fixed as a line with a length of 20 mm and a width of 1 mm.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Base Resin** & **Cured Depth** & **Cured Depth** & \\
**(Base Resin Only)** & **(Composite Resin)** & **Cured Image** \\  & **(\(\mu\)m)** & **(\(\mu\)m)** & **Cured Image** \\ \hline Resin A (FLHTAM02, & & & \\ Formlabs, Somerville, & 600 & 78 & \\ MA, USA) & & & \\ Resin B (3 DKH01-AJI3, & & & \\ Carima, Seoul, Korea) & 800 & 80 & \\ Resin C (Clear, Nasspop, & & & \\ Incheon, Korea) & 410 & 105 & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Cured depth according to the base resin (laser power for composite resin: 0.8 W).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Condition** & **3D Printing** & **Sintering** \\  & & **(Ref. Condition)** \\ \hline Average power (W) & 0.3 & 0.8 \\ Spot size (\(\mu\)m) & 100 & 20–100 (50) \\ Repetition rate & 90 & 20–90 (90) \\ Scan path interval (\(\mu\)m) & 50 & 1.25–50 (10) \\ Scanning speed (mm/s) & 3000 & 6.25–100 (50) \\ Layer thickness (\(\mu\)m) & 300 & 50 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Laser conditions for 3D printing and sintering.  
The 3D printing and laser processing was performed with a galvano scanner system (SCANcube III, SCANLAB, Munchen, Germany). Computer-aided manufacturing (CAM) software (EzCAD2, JCZ, Beijing, China) was used to generate various scan paths. To adjust the beam size for each process, a beam expander with a magnification range of 2-10\(\times\) was used. The smallest spot size used for sintering was 20 \(\upmu\)m with a 103 mm focal length F-theta lens. Scanning electron microscopy (SEM) (EVO10, Carl Zeiss, Jena, Germany) was used to observe the microstructure of the surface and cross-section. To simply measure the conductivity of the fabricated pattern, a digital multimeter (FLUKE115, FLUKE, Everett, WA, USA) was used. To improve the reliability of the resistivity measurement, the distance between each probe was fixed to 20 mm by an adjustment. The IV curves were measured to obtain the precise resistivity of the fabricated conductive pattern using a potentiostat/galvanostat (SP-50, BioLogic, Seyssinet-Pariset, France).