What Is Conformal Coating & How It Protects Your PCBs

December 15, 2025

What is Conformal Coating?

Conformal coating is a specially formulated paint used to protect printed circuit boards (PCBs) and related equipment from environmental erosion. It exhibits excellent resistance to high and low temperatures. Once cured, it forms a transparent protective film with superior properties including insulation, moisture resistance, leakage prevention, shock resistance, dust resistance, corrosion resistance, anti-aging, and corona resistance.

Under real-world conditions such as chemical exposure, vibration, high dust, salt spray, humidity, and high temperatures, PCBs can suffer from corrosion, softening, deformation, mold growth, and other issues, leading to circuit failures. Conformal coating is applied to the surface of the PCB, forming a protective film that guards against moisture, salt spray, and mold (the "three protections").

In environments containing chemicals (e.g., fuels, coolants), vibration, moisture, salt spray, humidity, and high temperatures, PCBs without conformal coating may corrode, grow mold, or experience short circuits, causing circuit malfunctions. Using conformal coating protects the circuits from damage, thereby improving PCB reliability, increasing the safety factor, and ensuring its service life. Additionally, because conformal coating prevents leakage currents, it allows for higher power and closer PCB trace spacing, facilitating component miniaturization.

Specifications and Requirements for Conformal Coating Process

Spraying Requirements:

1.Coating Thickness: Film thickness should be controlled between 0.05mm and 0.15mm. Dry film thickness should be 25μm to 40μm.
2.Secondary Coating: For products requiring high protection levels, a secondary coating can be applied after the initial film has cured (determined based on need).
3.Inspection and Repair: Visually inspect the coated board to ensure it meets quality standards and address any issues. For example, if coating gets on pins or other protected areas, use tweezers to hold a cotton ball dipped in PCB cleaner to wipe it off carefully, avoiding removal of the proper coating.
4.Component Replacement: After the coating has cured, to replace a component:
(1) Desolder the component directly with a soldering iron, then clean the area around the solder pad with a cloth dipped in PCB cleaner.
(2) Solder the replacement component.
(3) Use a brush to apply conformal coating to the soldered area and allow the film to surface dry and cure.

Operational Requirements:

1.The conformal coating workspace must be dust-free, clean, without airborne dust, have good ventilation, and restrict access to unauthorized personnel.
2.Operators must wear protective equipment such as masks or respirators, rubber gloves, and chemical safety goggles to prevent bodily harm.
3.After work, promptly clean used tools and securely close/seal containers holding the conformal coating.
4.Implement anti-static measures for PCBs. Do not stack PCBs. During coating, place PCBs horizontally.

Quality Requirements:

1.No running or dripping of coating on the PCB surface. When brush coating, avoid dripping onto locally masked areas.
2.The conformal coating layer should be even, smooth, uniform in thickness, and properly protect solder pads, SMD components, or conductor surfaces.
3.The coating surface and components must be free of defects and foreign matter such as bubbles, pinholes, ripples, shrinkage holes, or dust. There should be no chalking or peeling. Note: Do not touch the coating before it is surface dry.
4.Locally masked components or areas must not be coated.

Parts and Components That Should NOT Be Coated:

1.Typically Non-Coated Components: High-power heat sinks, heat spreaders, power resistors, high-power diodes, cement resistors, DIP switches, potentiometers (variable resistors), buzzers, battery holders, fuse holders, IC sockets, tactile switches, relays, connectors of these types, pin headers, terminal blocks, DB9 connectors, through-hole or SMD LEDs (non-indicator purposes), digital tubes, grounding screw holes.

Precautions for Conformal Coating Spraying Process:

1.PCBA must have process edges with a width not less than 5mm to facilitate conveyor轨道 movement.
2.Maximum PCBA dimensions: 410*410mm. Minimum dimensions: 10*10mm.
3.Maximum component height on PCBA: 80mm.

Introduction to PCB Conformal Coating Rework:

When a PCB needs rework, expensive components can sometimes be removed individually, discarding the rest. However, a more common method is to remove the protective coating from the entire board or specific local areas to replace damaged components one by one. When removing the conformal coating, ensure no damage is caused to the substrate beneath components, other electronic parts, or structures near the rework area. Methods for removing the protective film mainly include: using chemical solvents, micro-abrasion, mechanical methods, and soldering through the coating.

Using chemical solvents is the most common method. The key lies in matching the chemical properties of the coating to be removed with the specific solvent.