Pre-Coating Mandatory Operations: PCB Cleaning, Drying, Temperature & Humidity Control — 7 Critical Preparation Steps Prior to Nano-Conformal Coating Application

After soldering, PCBs are commonly contaminated with flux, rosin, grease and particulate pollutants. These residues severely weaken the adhesion of nano-conformal coatings, and may even trigger blistering or delamination of coatings. Thorough cleaning of PCBs is required prior to coating.

Isopropyl Alcohol (IPA) or dedicated cleaning agents are recommended, with ultrasonic cleaning or immersion scrubbing as applicable treatment methods. For PCBs manufactured via lead-free soldering processes, cleaning procedures shall follow IPC-CH-65B standards. Post-cleaning rinsing with deionized water is required to remove residual cleaning agents. Cleaning effectiveness can be evaluated through cleanliness testing specified in IPC-TM-650, whereby surface cleanliness is verified via ionic contamination testing.

Moisture may remain on PCB surfaces and within microvoids after cleaning. Direct coating application will trap moisture underneath the coating, resulting in bubbles or coating whitening. Therefore, baked drying is compulsory after cleaning.

Bake PCBs at 60–80°C for 15–30 minutes to ensure complete evaporation of moisture on PCB surfaces and within gaps between electronic components. Baking duration can be extended appropriately for multi-layer PCBs or PCBs with intricate structures. Upon completion of baking, allow the boards to cool naturally to ambient temperature in a dry environment before coating, so as to avoid condensation caused by temperature difference.

Ambient temperature and humidity directly affect the leveling property, curing rate and final film-forming quality of nano-conformal coatings. The working environment is recommended to maintain a temperature range of 15–35°C and relative humidity below 70%. For certain humidity-sensitive coating systems, relative humidity should be controlled within 60%.

Low temperature increases coating viscosity and impairs leveling; excessive temperature accelerates solvent volatilization and undermines coating uniformity. Excessively high humidity easily causes coating whitening, turbidity and other defects. Temperature and humidity monitoring instruments shall be deployed in the coating area, and a record-keeping system established to ensure environmental parameters stay within controlled ranges during each coating operation.

Regions on PCBs such as connectors, pins, gold fingers, sensors and debugging interfaces must not be covered by coatings. These areas shall be effectively masked with dedicated masking tapes or masking tooling before coating.

Low-residue masking materials are preferred to prevent adhesive residue after peeling. Custom masking fixtures are recommended for mass production to improve efficiency and consistency. After masking, full inspection is required to confirm complete coverage and avoid insufficient or excessive masking.

Potential incompatibility exists between different nano-conformal coating systems and PCB solder masks, silkscreen inks, potting adhesives and component packaging materials. Prior to formal mass coating, small-scale compatibility testing shall be conducted to confirm that the coating will not cause solder mask discoloration, ink peeling or adhesive softening.