Electronic assemblies operate in environments where moisture, dust, chemicals, vibration, and temperature swings can degrade performance over time. Two of the most widely used protection methods in PCBA manufacturing are conformal coating and low pressure molding. While both shield circuit boards from environmental threats, they differ significantly in materials, process, thickness, level of protection, and ideal use cases. Understanding these differences helps engineers and procurement teams ｓｅｌｅｃｔ the right protection strategy for their specific application.
Conformal coating is a thin polymeric film — typically 25 to 127 microns (1 to 5 mils) thick — applied to a completed circuit board. It conforms to the contours of the board and its components, creating a lightweight, transparent protective barrier against moisture, dust, chemicals, salt spray, and fungal growth.
Common conformal coating materials include:
Application methods range from automated spraying and selective spraying to dipping, brushing, and manual aerosol application. The coating is then cured through solvent evaporation, heat, UV light, or a combination of these. Selective automated spraying is particularly useful when only specific areas of a board need protection while keeping connectors and test points uncovered. Farway Electronic's conformal coating service supports boards up to 550 mm × 470 mm with selective masking, double-sided spraying and baking, and both fan and needle spraying modes, achieving average spraying times of 0.5 to 3 minutes per board.
Low pressure molding (LPM) is an encapsulation process that uses polyamide hot-melt resins — typically derived from bio-sourced materials such as castor oil — to fully surround and seal electronic components. The resin is injected at low pressure (under 60 bar) and moderate temperatures (180°C to 230°C), forming a solid protective shell around the assembly.
Unlike conformal coating's thin film, LPM creates a thicker, three-dimensional overmold that provides superior mechanical, chemical, and environmental protection. The process is completed in as few as three steps and cycle times can be as short as 50 to 90 seconds, significantly faster than potting, which often requires 24 hours to cure.
LPM is particularly suited for applications requiring:
Farway Electronic offers low pressure molding for electronics with support from technical consulting and engineering through product and mould development to full production, covering medical and industrial sensors, LED lighting, mobile-phone and power batteries, connector harnesses, circuit boards, and microswitches.
| Dimension | Conformal Coating | Low Pressure Molding |
|---|---|---|
| Thickness | 25–127 microns (thin film) | 1 mm and above (solid overmold) |
| Process | Spray, dip, or brush; then cure | Inject hot-melt resin into a mold |
| Cycle time | Minutes to hours (curing dependent) | 50–90 seconds per part |
| Application pressure | Minimal (atmospheric application) | Low (under 60 bar) |
| Processing temperature | Room temperature to ~150°C curing | 180°C–230°C injection |
| Weight added | Minimal | Moderate to significant |
| Transparency | Usually transparent | Opaque or colored |
| Reworkability | Moderate (can be stripped or dissolved) | Difficult (requires remelting) |
| Protection level | Light to moderate environmental | Heavy-duty; waterproof, vibration-resistant |
| Cost per unit | Lower | Higher; requires custom molds |
| Best suited for | Dense PCBs, cost-sensitive runs | Connectors, sensors, harsh environments |
Conformal coating is the right choice when you need lightweight, low-cost protection for populated PCBs operating in moderate environments. If the board encounters humidity, dust, or occasional condensation but is not submerged in water or subjected to heavy mechanical impact, a thin conformal film delivers adequate protection without adding bulk.
It is also preferred when:
For example, a communication device PCBA operating in an indoor environment benefits from conformal coating's thin, transparent barrier without the added bulk or cost of encapsulation.
Low pressure molding is preferable when the assembly needs true waterproofing (IP67 or higher), mechanical stress relief, or a self-contained protective housing without a separate enclosure. Because LPM forms a solid, three-dimensional shell, it absorbs vibration, resists impact, and seals out water far more effectively than a thin film.
Typical LPM applications include:
LPM also offers processing advantages over potting. Traditional potting involves mixing two-component compounds and waiting up to 24 hours for curing, whereas LPM uses a single-component thermoplastic resin that sets in under two minutes. This translates to higher throughput and lower labor costs per part.
Conformal coating and low pressure molding are not mutually exclusive. In many product designs, a PCBA receives conformal coating first to protect the board-level circuitry, and then key connectors or cable exit points are overmolded with LPM for mechanical strain relief and environmental sealing. This combined approach leverages the strengths of both technologies — thin-film protection across the board surface plus heavy-duty encapsulation at vulnerable interfaces.
For manufacturers seeking a partner that offers both capabilities under one roof, Farway Electronic provides integrated PCBA manufacturing services — from PCB fabrication and SMT assembly through conformal coating, low pressure molding, functional testing, and finished product assembly. The company's production lines include two SMT lines, two DIP plug-in lines, one conformal-coating spraying line, four low-pressure injection moulding machines, and two finished-product assembly lines, all backed by ISO 9001, ISO 13485, and IATF 16949 quality management systems.
The difference between low pressure molding and conformal coating comes down to protection level, process, and application. Conformal coating delivers a thin, cost-effective barrier for moderate environments, while low pressure molding provides heavy-duty encapsulation for harsh conditions. By understanding the strengths and limitations of each method, engineers can make informed decisions that balance performance, cost, and reliability. Partnering with an experienced manufacturer like Farway Electronic ensures both technologies are available and correctly applied to meet your product's specific requirements.
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