Conformal Coating for PCB Protection in Demanding Environments
From Bench to Field: Securing Your PCBA Against Environmental Stress
A PCB that performs flawlessly on the bench can fail in the field when the operating environment introduces moisture, condensation, chemical vapors, dust, or thermal cycling that the bare assembly wasn’t designed to withstand. Conformal coating is the engineering solution to that gap — a thin, protective layer applied to the assembled board that seals sensitive components and circuitry against the environmental factors most likely to degrade performance or cause failure over time.
At ETI, conformal coating is an in-house capability, not a subcontracted afterthought. It’s the final protective step in a fully integrated PCBA process — applied with the same process discipline, documentation rigor, and IPC-certified oversight that governs every stage of assembly before it.
WHY IT MATTERS
Why Conformal Coating Matters for High-Reliability Applications
For engineering managers specifying assemblies destined for harsh or variable operating environments, conformal coating isn’t an optional upgrade — it’s often the difference between a product that meets its rated service life and one that doesn’t.
The industries ETI serves operate in some of the more demanding environments electronics encounter. HVAC equipment experiences wide temperature swings and condensation. Agricultural machinery operates in humid, chemically active environments with exposure to fertilizers, pesticides, and dust. Industrial controls in food processing and manufacturing face washdown conditions and airborne contaminants. Medical devices must maintain performance through sterilization cycles, body fluid exposure, and long-term implant or near-patient use. Aerospace electronics face altitude-driven pressure changes, vibration, and thermal extremes.
In all of these contexts, an uncoated PCB is a reliability liability. Conformal coating PCB applications address that liability by creating a dielectric barrier that resists moisture absorption, deters dust and fungus growth (dust can be a particular enemy of a board), inhibits corrosion on exposed metal surfaces, reduces the risk of electrochemical migration between adjacent conductors, and provides a degree of mechanical protection against vibration-induced fatigue at component leads and joints.
Conformal Coating Materials: Selecting the Right Chemistry for Your Application
Not all conformal coatings perform the same way, and the right material choice depends on your operating environment, temperature range, chemical exposure profile, and rework requirements. ETI works with customers during the design and DFM process to select the coating chemistry that fits the application — not just the one that’s easiest to apply.
Silicone Conformal Coating
Silicone is ETI’s primary conformal coating material. We most commonly use Dow Corning 1-2577. This material contains a UV tracer, allowing inspection under black light in a dark room to ensure complete coverage. Silicone maintains flexibility and dielectric properties across a wide temperature range and provides excellent moisture resistance.
Urethane Conformal Coating
Urethane coatings offer superior chemical resistance compared to acrylics — particularly against fuels, solvents, and hydraulic fluids — making them well-suited for industrial, automotive, and aerospace-adjacent applications where chemical exposure is a design consideration. The trade-off is reworkability: urethane coatings are significantly more difficult to work with than acrylics and typically require mechanical abrasion or specialized stripping chemistry. For assemblies unlikely to need rework, that trade-off is often acceptable. When urethane is required, we typically apply it from spray cans.
Parylene Conformal Coating
Parylene is in a different category from the liquid-applied coatings above. Applied through a chemical vapor deposition (CVD) process, parylene forms a truly conformal, pinhole-free polymer film that penetrates and coats all surfaces of the assembly — including crevices, undersides of low-standoff components, and internal geometries inaccessible to liquid coating methods. The result is the most uniform, defect-free coating achievable, with exceptional moisture barrier properties, biocompatibility, and chemical inertness. Parylene coating is subcontracted to qualified partners when required for specific customer applications (primarily aeronautics).
Acrylic Conformal Coating
Acrylic conformal coating is the most widely used coating type in electronics manufacturing and the baseline choice for a broad range of commercial and industrial applications. Acrylics offer good moisture and humidity resistance, excellent dielectric properties, and — critically — straightforward reworkability. Because acrylic coatings are soluble in common solvents, localized removal for rework or repair is practical without damaging surrounding components or board finish. For programs where field repairability matters, acrylic is typically the preferred starting point.
Epoxy Conformal Coating
Epoxy coatings provide the hardest, most abrasion-resistant coating surface of the standard conformal coating types. They offer strong chemical and moisture resistance and are well-suited for applications where physical protection against particulate abrasion or direct contact is a requirement alongside environmental protection. The significant limitation is reworkability — epoxy coatings are essentially permanent and require mechanical removal that risks board and component damage.
HOW IT WORKS
The Conformal Coating Process at ETI
Pre-Coating Preparation
Board cleanliness is foundational to coating adhesion and performance. Flux residues, contamination from handling, and ionic contaminants left on the board surface compromise the coating’s bond to the substrate and can cause delamination or electrochemical activity under the coating over time. ETI’s pre-coating preparation process ensures boards arrive at the coating station in the condition required for consistent, well-adhered coating application. For most no-clean flux processes, boards do not require washing prior to coating. Customer-specified or critical assemblies are washed before coating.
Masking and Keep-Out Zone Management
Connectors, edge fingers, test points, heat sink mounting surfaces, and adjustment components must be kept free of coating. ETI’s process includes masking of all defined keep-out zones prior to coating application, with post-coat inspection to verify that protected areas remain clear. Areas such as connectors, vented electrolytic capacitors, switches, and unsealed relays must remain uncoated.
Curing
Coating performance depends on complete cure. Curing is performed in a thermal oven, with parameters matched to the coating chemistry and application. Cure parameters are documented and controlled as part of ETI’s ISO 9001:2015 certified process.
Inspection and Verification
Post-coating inspection verifies coverage of required areas and cleanliness of keep-out zones. Most conformal coatings used in electronics manufacturing include fluorescent additives that fluoresce under UV illumination, making coverage verification practical and objective. ETI performs black-light UV inspection leveraging the UV tracer in our primary silicone coating. IPC-A-610 workmanship criteria apply to conformal coating application quality.
PROJECT BENEFITS
Conformal Coating Benefits for ETI Customers
Environmental Protection Where It’s Actually Needed
Coating chemistry and coverage are selected for your specific application environment — not applied generically. The right coating for an agricultural equipment controller operating in a chemically active field environment is different from the right coating for a medical device in a controlled clinical setting.
Repeatable, Documented Application
Selective robotic application and documented process parameters mean your coating process is repeatable across every board in every production run — with the traceability to demonstrate it.
Single-Source Integration
Conformal coating at ETI is the final step in an assembly process that began at solder paste screen printing and passed through reflow, soldering, AOI, and X-ray under one roof. There’s no outbound shipment to a coating subcontractor, no re-inspection risk, and no break in the chain of custody between assembly and coating.
Support for Regulated Applications
For customers in medical, aerospace, and other regulated industries, ETI’s conformal coating process is documented, certified under ISO 9001:2015, and executable to IPC-A-610 workmanship standards — supporting the quality evidence requirements of design history files, first article inspections, and production lot records.
Coating Selection Expertise
ETI’s engineering team works with customers during DFM review to select and qualify the right coating material for the application — not after the board is built, when changing the coating type requires requalification.
PCB Conformal Coating Types: Quick Reference for Design Engineers
For engineers early in the design process who need a fast reference on conformal coating material selection:
Acrylic offers the best balance of protection and reworkability for general industrial and commercial applications. Urethane adds chemical resistance for fuel, solvent, and hydraulic fluid environments at the cost of rework difficulty. Silicone handles thermal extremes that other chemistries can’t sustain. Epoxy provides the hardest, most abrasion-resistant surface for physically demanding environments. Parylene delivers the most uniform, defect-free barrier available — ideal for medical, implantable, and highest-reliability applications where no other coating method achieves the same coverage.
If you’re specifying a coating for a new design and aren’t sure which chemistry fits your application, ETI’s engineering team can work through the selection with you before the first board is built.
Ready to Discuss Conformal Coating for Your Assembly?
Whether you’re specifying coating for a new design, qualifying a coating process for a regulated application, or looking for a contract manufacturing partner who handles coating in-house rather than farming it out, ETI’s team is ready to get into the details with you.