What is the Function of PCB Conformal Coating? Essential Protection Process & Selection Guide for Industrial Control Mainboards

Is PCB Conformal Coating Really Necessary? Why Must Mainboards of Industrial Power Supplies, PLCs and Inverters Apply Conformal Coating? This article elaborates on the core functions, technical parameters, applicable scenarios, selection pitfalls and mass production cases of conformal coating. It helps manufacturers select and apply conformal coating properly to reduce circuit board failures caused by corrosion and after-sales rework rates.
Many small and medium electronics manufacturers and industrial equipment suppliers face a common problem: all prototypes pass testing, yet mass-produced units frequently suffer mainboard leakage, short circuits, black screens and unstable signals after delivery. Troubleshooting reveals that these issues stem not from flawed circuit design, but insufficient basic protection on PCBs. Mass failures arise due to moisture, dust accumulation and slight corrosion. As an essential protection process for industrial control mainboards and new energy circuit boards, PCB conformal coating offers a core solution to such hidden risks in mass production. However, most purchasers and junior engineers lack thorough understanding, which often leads to improper model selection and incorrect application, resulting in unnecessary production costs and higher rework risks.
1. Core Functions of PCB Conformal Coating (Beyond Moisture and Mold Resistance)
PCB conformal coating is a polymer protective film applied onto the surface of PCBA. The industry term “three-proofing” refers to moisture resistance, mold resistance and salt spray resistance. It also delivers multi-dimensional protection including dust resistance, acid & alkali corrosion resistance, anti-electrochemical migration, dielectric withstand voltage and anti-aging performance, serving as a standardized mass-production process for industrial circuit boards.
Its working principle is to form a dense, transparent insulating film covering components, solder pads and circuit traces. It blocks contact between circuit conductors and moisture, dust, salt mist and corrosive gas in the air to fundamentally prevent circuit board failures. It is especially suitable for industrial equipment operating continuously, deployed outdoors or working in humid workshops.
Tangible benefits for manufacturers: drastically reduce mass defects such as short circuits, electric leakage, crystal oscillator frequency drift, poor contact and copper foil oxidation. It effectively extends the service life of industrial control mainboards and power equipment, cutting after-sales rework and customer complaints.
2. Key Basic Parameters of Mainstream Conformal Coatings (Must-read for Procurement & Selection)
Small and micro enterprises do not need to overcomplicate parameter screening. Focus on four core indicators for mass production to meet the demands of standard industrial control and new energy equipment:
Curing Thickness: 20～80 μm in general. Thin coating will not affect component heat dissipation or connector plugging. Avoid cracking caused by excessive thickness or insufficient protection due to overly thin coating.
Dielectric Strength: ≥10 kV/mm. It ensures stable insulation of high-low voltage industrial control boards and power supply boards and prevents high-voltage leakage.
Operating Temperature: -40℃～125℃, adaptable to cyclic temperature changes in workshops and day-night temperature fluctuations for outdoor equipment.
Environmental Standard: RoHS compliant, benzene-free and low odor, satisfying domestic mass production requirements and routine export inspection standards.
Three mainstream types are available:
Acrylic conformal coating: cost-effective and easy for rework
Polyurethane conformal coating: outstanding corrosion resistance and weatherability
Silicone conformal coating: excellent heat resistance, ideal for high-power heat-generating mainboards
Select the proper type according to actual working conditions.
3. Applicable Scenarios Requiring Conformal Coating (Widely Adopted by 90% Industrial Control Manufacturers)
Conformal coating is not mandatory for all circuit boards. Nevertheless, mass failures are highly likely to occur without coating in the following scenarios, making it an indispensable industry process:
Industrial Control Equipment: PLC mainboards, inverters, servo drives, industrial data acquisition boards (workshops with heavy dust, high humidity and abundant acid-base gas)
New Energy Equipment: Charging pile control boards, photovoltaic inverters, energy storage power mainboards (exposed outdoors under intense sunlight, wide temperature variation and heavy salt spray erosion)
Vehicle-mounted & Outdoor Equipment: Vehicle controllers, outdoor monitoring mainboards, communication power supplies (long-term vibration, high humidity and drastic day-night temperature difference)
Coastal Humid-region Equipment: Coastal industrial control devices, marine control boards (high salt spray concentration easily triggers copper foil oxidation and short circuits)
Small consumer electronics boards operating in fully enclosed, dry and dust-free indoor environments may skip coating. For industrial control, new energy and outdoor equipment, conformal coating is a baseline mass-production process.
4. Common Selection & Application Pitfalls for Manufacturers (Main Causes of Mass Production Defects)
Most conformal coating failures do not originate from poor product quality, but misunderstandings in selection and construction. New purchasers are prone to these traps:
Pitfall 1: Thicker coating equals better protection. Excessively thick coating traps air bubbles and hinders component heat dissipation. It tends to crack and peel under high temperature, weakening protection. Thin and uniform coating is the key.
Pitfall 2: One conformal coating fits all circuit boards. Ordinary acrylic coating ages and peels easily on heat-intensive power mainboards under sustained high temperature. Standard grades lack sufficient weatherability for outdoor salt spray environments and lead to rapid board corrosion.
Pitfall 3: Full-board coating without masking. Blind coating on interfaces, buttons, terminals and battery sockets causes poor contact and plug failure, bringing extremely high rework costs.
Pitfall 4: Direct coating without surface cleaning. Residual flux, oil stains and dust on PCBs reduce coating adhesion, triggering partial peeling and localized corrosion leakage.
5. Targeted Selection Suggestions (Direct Reference for Beginners, Minimize Trial & Error)
Based on mass-production demands of small and micro manufacturers, we simplify selection logic to avoid repeated testing. Match products according to working conditions:
General industrial control, indoor power boards requiring rework and debugging: Choose acrylic conformal coating. Fast curing, cost-efficient and convenient for rework, suitable for mass production.
Outdoor equipment, charging piles and coastal salt spray environments: Choose polyurethane conformal coating. Superior salt spray resistance, hydrolysis resistance and anti-corrosion performance for long-term outdoor service.
High-power inverters and high-temperature heat-generating mainboards: Choose silicone conformal coating. Excellent heat resistance balances protection and heat dissipation for high-heat power boards.
6. Real Mass-production Application Case
A small industrial equipment manufacturer based in Dongguan mainly produces workshop PLC control boards. To cut costs, conformal coating was omitted in the early stage. Three months after shipment, mass defects including signal drift, standby leakage and failure to power on appeared, pushing the after-sales rework rate up to 15%. Testing confirmed the root cause: moisture and dust accumulated on circuit boards, triggering micro-corrosion of copper foil and insulation degradation.
Solution: Standardized acrylic conformal coating was adopted for all mainboards, with standardized procedures including PCB surface cleaning, precise masking and uniform thin-layer coating. After rectification, the equipment failure rate dropped below 1%, greatly cutting after-sales costs and improving product stability and customer recognition.
7. Conclusion
PCB conformal coating is not an optional upgrade process, but a baseline mass-production process for industrial control, new energy and outdoor electronic equipment. Appropriate product selection and standardized construction can eliminate mass defects induced by humidity, salt spray and corrosion at the source. It helps manufacturers reduce testing cycles, lower rework costs and stabilize product quality.
If your factory manufactures industrial power supplies, PLCs, inverters or charging pile equipment and you are unsure which conformal coating fits your working conditions, provide your equipment operating environment and mass production requirements to obtain targeted selection proposals and sample testing support.