FPCWAY

Preparation of FPC based on ultrasonic spraying method_4_Experimental Results

3. Experimental Results

3.1 Conductivity Testing and Analysis

The conductivity of the circuit was judged by measuring the sheet resistance of the conductive lines with different numbers of spray layers. To ensure the accuracy and authenticity of the experimental data, five random points were selected for testing on each individual sample, and then the average value and error range were calculated. Table 1 shows the impact of different numbers of spray layers (each layer sprayed under the conditions of a solution feed rate of 0.15 mL/min and a nozzle movement speed of 20 mm/s) on the circuit sheet resistance. As the number of spray layers increases, the sheet resistance steadily decreases, and the corresponding error also narrows. In actual industrial production, it is generally considered that a sheet resistance of less than 100 mΩ/sq is already a very good conductive effect. Therefore, under the experimental conditions of this study, excellent conductivity can be achieved when the number of spray layers reaches 6 or more.

3.2 Macroscopic Morphology and Edge Roughness

Based on the results of the conductivity tests, circuits with 6 to 8 spray layers were selected for subsequent related tests. The edge morphology of the 8-layer sprayed circuit was observed under a microscope. Figure 6a shows the morphological characteristics of the circuit at a magnification of 30 times, with the corners clearly demonstrated; a randomly cropped image of a portion of the rough edge (see Figure 6b) was used to calculate the corresponding roughness proportionally. It was found that the edge roughness error could be controlled within 0.05 mm (50 μm), indicating that the resulting lines are smooth and flat.

3.3 XRD and SEM Characterization

Figure 7 shows the X-ray diffraction spectrum of a 6-layer sprayed sample. Obvious peaks are observed near 38°, 44°, and 64°, which correspond exactly to the diffraction angles of silver. Due to the presence of the substrate PI film's diffraction, there is some background noise, but it is sufficient to prove that the wires on the substrate are composed of pure silver.

By observing the microstructure of the silver wire surface through SEM, the results are shown in Figure 8. It can be seen that the microstructure of the lines is uniform and flat, which verifies the high precision characteristics of the ultrasonic spraying method.