Characterization of Commercial Solder Mask in Printed Circuit Board Application

Solder mask (SM) has been widely utilized in the printed circuit board (PCB) to prevent solder bridging and to passivate against the outer environment. In the PCB assembly process, SM experienced chemical treatment and reflow soldering at elevated temperatures, causing SM to undergo chemical changes and thermal degradation. The objective of this work is to characterize the thermal, surface, and chemical properties as well as the hydrophilicity of the commercial SM. The SM samples were prepared by mechanical scraping of commercial PCB and were evaluated using the TGA and DSC. The surface morphology, roughness, and chemical compositions of SMs were investigated using SEM/EDX, AFM, and FTIR, respectively. The results indicated that the thermal decomposition temperature (Td) and the glass transition temperature (Tg) of the commercial SM are observed at 398.91 °C and 128.7 °C, respectively. Significant Ba, S, and O contents were detected at the SM cross section in the SEM/EDX analysis, indicating a pronounced usage of BaSO4 fillers, which concurred with the FTIR and XRD results. The crystallite size of BaSO4 fillers was calculated as 40.97 nm based on the Scherrer equation from XRD peaks. Besides, strong peaks of C=O and C–O in FTIR suggested the presence of epoxy acrylate. AFM result indicated a surface roughness root mean square (RMS) at 122.26 ± 13.24 nm, which suggests a smooth SM surface. Lastly, a low water contact angle of 57.68° suggested the hydrophilic nature of commercial SM, while the surface energy of SM at 49.22 mJ/m2 implied a good surface adhesion with other components in PCB.