# Partial Discharge Inception and Breakdown Voltage Analysis in PCB-Based Electrode Structures
## 2 Experimental Setup and PCB Fabrication
### Production of PCB Defect Samples  
Within the field of power electronics, a range of circuit board materials are utilized, with common options including flame-retardant materials (e.g., FR-1 to FR-6) and composite epoxy materials (e.g., CEM-1 to CEM-5). For the purposes of this study, the FR-4-86 fiberglass board was selected due to its established standard thickness of 1.6 mm, copper foil thickness of 35 \(\upmu\)m, and its optimal balance of mechanical strength, electrical insulation, and cost-effectiveness. Compared to alternatives like polyimide, which offers higher thermal resistance, or PTFE, known for excellent dielectric properties but lower mechanical robustness, FR-4 is well suited for high-voltage PCB applications. Five distinct electrode configurations were fabricated to simulate PD under various conditions. These designs were selected to enable the evaluation of key electrical parameters, such as PDIV and breakdown voltages.  
* Parallel electrode (PE) sample: The first configuration comprised two Pes, each 5 mm in diameter and 26 mm in length, with a 0.5 mm gap between them. Discharges occurred between the parallel plates, as shown in Figure 2a.
* Triangular electrode (TE) sample: The second design featured a triangular upper electrode with a base and height of 7.2 mm, and a 90\({}^{\circ}\)-angled tip. This electrode was situated above the lower electrode, and the separation between them was maintained at 0.5 mm (Figure 2b).
* Right-angled electrode (RE) sample: This configuration incorporated a 90\({}^{\circ}\) corner in the upper electrode, which measured 19 \(\times\) 15 mm and featured rounded edges. The gap between the upper and lower electrodes was again 0.5 mm, with discharges primarily occurring at the corner junction (Figure 2c).
* Floating electrode (FE_0.5 mm) sample: The next design included a 1 mm-diameter FE positioned centrally between two main electrodes (5 mm in diameter and 26 mm in length), separated by 2 mm. This configuration simulated the discharges in the central region between the electrodes (Figure 2d).
* Floating electrode (FE_0.3 mm) sample: This sample was similar to the previous configuration but incorporated a larger FE (1.4 mm diameter) and reduced the spacing between the main electrodes to 0.3 mm (Figure 2e).  
To ensure appropriate coverage during the fabrication process, extra material was intentionally left around the electrodes to facilitate the application of the epoxy resin. The resin used was a bisphenol A formulation mixed with polyoxypylene diamine at a 3:1 ratio for optimal curing. The final product exhibited minimal bubble formation and a clear and consistent finish.  
The selected electrode configurations were specifically designed to investigate the effects of different electrode shapes and insulation gaps on the PD behavior. The PE sample, with its uniform electric field, served as a baseline, offering a clear reference point for the discharge characteristics. Conversely, the TE and RE samples created non-uniform electric fields, which facilitated this study of how changes in the electrode geometry affected the PD dynamics.  
The FE samples, which featured insulation gaps of 0.5 and 0.3 mm, allowed a detailed exploration of how varying clearance distances between electrodes influenced discharge behavior. By comparing these distinct configurations, this study provides a thorough examination of the factors that govern PD under different conditions, contributing valuable insights into how the electrode design and gap size affect PD characteristics.