Influence of de-paneling on moisture incubation and challenges in PCB reliability under highly humid conditions

Moisture ingress critically affects the reliability of printed circuit boards (PCBs) under high-temperature and high-humidity conditions by accelerating failure mechanisms such as conductive anodic filament formation, dendrite growth, and delamination, while degrading dielectric performance. Although protective coatings are typically applied to mitigate moisture penetration, the de-paneling process used to separate PCBs after fabrication exposes fresh edge surfaces containing microcracks that facilitate moisture diffusion. Despite its practical importance, the quantitative influence of de-paneling techniques on moisture transport behavior has not been clearly established. In this work, the moisture diffusivity of PCBs prepared using two common de-paneling methods, namely cost-effective V-cut and precision CNC routing, is systematically investigated. Capacitance monitoring and gravimetric measurements were conducted under controlled humidity conditions to capture transient moisture absorption behavior, and finite-element modeling based on Fick’s diffusion law was employed to extract diffusivity parameters. The results reveal that V-cut PCBs exhibit substantially higher mean moisture diffusivity than CNC-routed boards (1.24 × 10^⁻13 m²/s & 8.37 × 10^⁻15 m²/s at 50 °C/90% RH, and 1.03 × 10^⁻12 m²/s & 1.64 × 10^⁻14 m²/s at 60 °C/90% RH), together with greater variability and longer saturation times (99.02 h vs. 81.54 h at 50 °C/90% RH and 92.69 h vs. 80.38 h at 60 °C/90% RH). Surface analysis further shows higher edge roughness for V-cut samples (R_rms = 0.1322) compared to CNC-routed boards (R_rms = 0.0885), where microcrack formation at the V-groove significantly accelerates moisture ingress. These findings quantitatively demonstrate that the de-paneling technique strongly governs moisture diffusion and environmental reliability in PCBs.