Moisture is a significant threat to rigid printed circuit boards (PCBs), as it can degrade electrical performance, promote corrosion, and cause physical damage like delamination. Implementing effective moisture-proof and dehumidification measures is essential to ensure the reliability and longevity of PCBs, especially in humid environments such as industrial facilities, coastal areas, or outdoor electronics.

　　Material selection is the first line of defense. Using moisture-resistant substrate materials, such as high-Tg (glass transition temperature) FR-4 or polyimide, reduces water absorption. High-Tg FR-4, with a glass transition temperature above 170°C, absorbs less moisture than standard FR-4, maintaining stable dielectric properties even in humid conditions. Additionally, applying a conformal coating—a thin polymeric film (e.g., acrylic, silicone, or urethane)—over the PCB surface creates a barrier against moisture, dust, and chemicals. Conformal coatings are particularly effective for PCBs in harsh environments, as they conform to the board’s topography, covering exposed components and traces without interfering with functionality.

　　Manufacturing processes include steps to minimize moisture retention. After fabrication, PCBs undergo baking at controlled temperatures (typically 125°C for 2–4 hours) to remove trapped moisture before assembly. This is critical for multi-layer PCBs, where moisture can get trapped between layers during lamination. During soldering, using nitrogen reflow soldering creates an inert atmosphere, reducing oxidation and preventing moisture from being absorbed during high-temperature processes, which could lead to "popcorning" (component damage from steam expansion).

　　Storage and handling protocols are equally important. PCBs should be stored in sealed, moisture-barrier bags (MBBs) with desiccants (e.g., silica gel) to maintain a low relative humidity (RH) environment—ideally below 30%. Desiccants absorb moisture from the air, preventing condensation on the PCB surface. For long-term storage, vacuum-sealed MBBs with humidity indicators (which change color if RH exceeds a threshold) provide an extra layer of protection. When handling PCBs, workers should use anti-static gloves to avoid transferring oils or moisture from skin, and boards should be acclimatized to ambient conditions before opening MBBs to prevent condensation (a process called "equilibration").

　　Active dehumidification in operational environments ensures ongoing protection. Enclosures housing PCBs can be equipped with desiccant packs or built-in dehumidifiers (e.g., Peltier-effect devices) to maintain RH levels below 50%. For outdoor electronics, weatherproof enclosures with gaskets prevent rain and humidity ingress, while ventilation systems with filters reduce moisture buildup. In industrial settings, climate-controlled rooms with dehumidifiers ensure consistent low humidity during PCB assembly and testing.

　　Regular maintenance includes periodic inspections and reapplication of protective coatings. Visual checks for corrosion, delamination, or coating damage can catch moisture-related issues early. For critical applications, such as aerospace or medical devices, PCBs may undergo humidity testing (e.g., IPC-6012 standards) to verify resistance to prolonged moisture exposure.

　　By combining material science, manufacturing best practices, proper storage, and active environmental control, these measures effectively protect rigid PCBs from moisture, ensuring reliable performance in diverse operating conditions.