Is Conformal Coating Waterproof? Understanding Moisture Protection for PCBAs

What Conformal Coating Actually Does

Conformal coating is a thin polymeric film applied to a printed circuit board assembly to protect it from moisture, dust, chemicals, salt spray, and temperature fluctuations. The coating conforms to the contours of the board and its components, forming a protective barrier typically 25 to 210 micrometres thick. Its core functions are to insulate conductors, prevent corrosion of solder joints and traces, suppress electrochemical migration, and reduce the risk of short circuits caused by condensation.

For the majority of indoor and moderate-environment electronics, this level of protection is more than adequate. Coated boards withstand high humidity, condensation cycles, and occasional splashing far better than bare assemblies. However, the coating is applied as a thin film, so it does not create a sealed, hermetic enclosure. Prolonged immersion or high-pressure water exposure can eventually penetrate coating edges, connectors, and unmasked interfaces.

How Different Resin Chemistries Handle Water

Not all coatings behave identically when exposed to moisture. The resin chemistry you choose directly determines how the film performs under humid and wet conditions. The four most common chemistries used in PCBA manufacturing are compared below.

Silicone and polyurethane coatings are the most frequently specified when humidity, salt spray, or condensation are a concern. Silicone in particular retains flexibility across wide temperature ranges, which helps the film resist cracking during thermal cycling — a common failure mode that lets moisture penetrate otherwise protected areas.

What “Waterproof” Really Means in Electronics

When engineers ask whether a coating is waterproof, they are usually referring to an IP (Ingress Protection) rating. The IP system, defined by IEC standard 60529, classifies how well an enclosure resists solids and liquids. A conformally coated board mounted inside a suitable housing can help a product achieve ratings such as IP54 or IP65, which protect against splashing or low-pressure water jets. However, ratings like IP67 or IP68 — which imply immersion — almost always require additional sealing measures beyond the coating film itself.

In practice, the coating delivers reliable protection against the conditions most electronic products actually face: humid air, condensation, temperature swings, airborne contaminants, and occasional splashing. For applications that demand genuine immersion protection, manufacturers typically pair coating with low-pressure injection moulding, potting compounds, or mechanical seals at connectors and enclosure interfaces.

When You Need More Than Coating Alone

For many product categories, conformal coating is the right and sufficient answer. But when a board must survive sustained moisture exposure, automotive under-hood conditions, medical sterilisation cycles, or outdoor weathering, coating is often combined with a secondary barrier. What is conformal coating used for in these combined protection schemes? It serves as the first line of defence on the board surface, while a thicker encapsulant provides the structural waterproofing.

Low-pressure injection moulding is one of the most effective complementary processes. Hot-melt polyamide or polyurethane resin is injected at low pressure around the coated assembly, fully encapsulating sensitive components and connectors. The result is a solid, waterproof module that withstands immersion, vibration, and chemical exposure. This approach is widely used in automotive sensors, medical devices, LED lighting modules, and battery management systems.

Choosing the Right Manufacturing Partner

Selecting the correct coating chemistry and deciding whether encapsulation is needed requires both materials knowledge and production capability. A capable electronics manufacturing partner should offer automated conformal coating lines, selective masking for connectors and test points, controlled curing, and the ability to integrate coating with downstream processes such as low-pressure moulding and functional testing.

Farway Electronic, based in LongGang, Shenzhen, operates an automated conformal coating spraying line that supports boards up to 550 mm × 470 mm, including dense and high-pin-count assemblies. The line accommodates selective masking, double-sided spraying and baking, and both fan and needle spraying modes. For products that need higher protection, Farway also runs four low-pressure injection moulding machines for encapsulating sensitive electronics, alongside its SMT, DIP, testing, and finished-product assembly capabilities. With ISO 9001, ISO 13485, IATF 16949, and ISO 14001 certifications, Farway serves automotive, medical, new energy, security, and industrial electronics customers who require documented, traceable moisture protection rather than assumptions.