Energy and Electronics Coatings

These are coatings where the film is a working component rather than a finish, and they are developed against a measurement. A battery cell coating has to be electrochemically stable and dimensionally precise. A conformal coating has to insulate without trapping heat. A solar backsheet coating has to survive twenty-five years outdoors. In each case the film carries a duty that is measured in ohms, volts per micron, watts per metre kelvin or hours of exposure, and appearance is a secondary consideration.

The electrical grades in this range are specified by resistivity, and the decades matter more than the words. Anti-static surfaces are usually taken as 1×10^9 to 1×10^11 ohms per square, static-dissipative as 1×10^6 to 1×10^9, and conductive fills as 1×10^2 to 1×10^4 for carbon and lower for metal. A surface intended to attenuate a radiated field is a separate case again and is run below 1 ohm per square, because attenuation follows conductivity and an unbroken ground path rather than the label conductive. Those bands are orders of magnitude apart, so a coating specified only as anti-static tells a design engineer very little. Resistivity is also a function of film thickness, cure state and test humidity, which is why we state the method, ASTM D257, alongside the number and why we ask for the conditioning the customer intends to test at.

Conformal coatings divide by chemistry before they divide by grade. Acrylic films dry quickly, inspect well under ultraviolet light and can be removed locally with solvent, which makes them the usual choice where boards are reworked. Urethane films give better solvent and abrasion resistance and are harder to repair. Silicone films hold their flexibility across a wide temperature range and suit assemblies that run hot or cycle widely, at a further cost in repairability. Parylene, deposited by vacuum from the vapour phase, gives the thinnest and most uniform coverage of the four and is effectively not repairable at all; it is a vacuum deposition process rather than a liquid coating, and it is named here as the far end of the scale rather than as part of this range, which covers the acrylic and silicone chemistries. That trade-off between protection and serviceability is the first question in any conformal specification, and it is a decision about the customer’s production and field-service model, not only about the film.

Thermal and outdoor grades are governed by the same honesty. A high-emissivity coating raises radiative loss from a surface and a filled coating shortens the conduction path across an insulating layer, but a film 30 to 150 microns thick sits in series with every other resistance in the assembly and cannot substitute for a heat sink, a fan or a redesigned airflow path. The radiative gain is also conditional: bare bright metal starts at a total emittance of around 0.05 to 0.2 and gains a great deal, while an anodised, painted or already dark matt surface starts high and gains little. For solar hardware, frames, rails, junction-box housings and backsheets have to hold adhesion, insulation and colour through ultraviolet exposure, damp heat and thermal cycling for the module’s service life. These are coatings specified on measured functional properties, and every project starts as a development brief with the customer rather than a product selection. Work is carried out at our technical centre and laboratory in Greater Noida, with the production line built for batch-to-batch consistency once a grade is fixed.

Electrically insulating, electrolyte-resistant films for cell casings, can exteriors, current-collector hardware, busbar supports and module housings, applied at a controlled build so cell dimensions and creepage distances stay inside the design.

Thin protective films over populated boards for moisture, condensation, dust and contaminant resistance, supplied in acrylic and silicone chemistries and selected against the customer’s service temperature and rework policy.

Surface-resistivity control across the anti-static, dissipative and conductive decades for handling trays, films, enclosures and grounded or shielding faces, with the shielding duty served only by the metal-filled grade.

High-emissivity radiating films and filled thermally conductive films used to raise radiative loss from a surface and to shorten the conduction path across an insulating layer.

Anti-soiling front-glass topcoats and durable exterior coatings for backsheets, frames, rails and junction-box housings, specified against the twenty-five year outdoor design life normally set for a module.

The figures below are the typical operating window for this range, not a measured result for any one batch. Confirmed values are issued with the Technical Data Sheet and Certificate of Analysis by our laboratory.

These coatings are applied by the same equipment as decorative finishes, but they are judged by a measurement rather than by eye, so the process window is narrower and the inspection step is different. The controlling variable in almost every case is film thickness. Resistivity, dielectric withstand, shielding continuity, thermal resistance and transmission loss all move with build, and they move at the thinnest point rather than at the average. A coating that meets its resistivity target on a flat panel at 40 microns can fail on a moulded rib at 12 microns, so film build is verified on the part, at the worst-case geometry, not on a test plaque sprayed alongside it.

Surface preparation is the second control. Electrically functional films need a clean, dry, contaminant-free surface with the specified pre-treatment in place: chromate-free conversion coating or anodising on aluminium, phosphate on steel, flame or plasma treatment on polyolefins, and a verified cleaning step on glass. On printed circuit assemblies, cleanliness governs both adhesion and long-term insulation resistance. Ionic residue trapped under a conformal coating will draw moisture and create leakage paths that no amount of film build will correct, so we specify the flux regime and the cleaning or no-clean policy before we specify the coating.

Masking is a production issue that is often underestimated. Terminals, weld zones, connectors, test points, earth bosses, gasket lands, heat sink contact faces and thermal interface pads must stay bare, and the boundary between coated and bare has to be repeatable at line rate. For selective conformal coating, programme edge keep-out is defined against the tallest component and the connector body, and coverage is inspected under ultraviolet light using the trace additive in the acrylic grade. For conductive and shielding grades, the opposite applies: contact pads and mating edges have to be fully coated and left free of overspray from any later layer. Grounding and shielding are also separate duties. Ground continuity is measured across the assembled enclosure rather than on a single panel, and where attenuation of a radiated field is required the metal-filled grade is specified and the assembly is measured, because a panel resistivity figure does not predict what a seam, a vent or an unbonded door will do.

Cure is what converts an applied film into the property that was specified. Stoving grades are controlled to metal temperature and dwell, not oven set point, and thick sections and heavy castings lag the schedule. Two-component grades develop their final electrical and mechanical properties over days rather than minutes, and moisture-cure silicones depend on water vapour reaching the film, so heat brings the surface to handling strength without shortening the full cure. Proof testing too early gives a pessimistic result in every one of these cases. Coil-coated solar hardware is controlled to peak metal temperature and line speed, and cut edges, punched holes and drilled fixing points created after coating are the usual origin of first-year corrosion on a frame or rail.

Finally, expectations have to be set on thermal grades. Raising emissivity on a bright metal surface or shortening the conduction path across an isolation layer both give real, measurable gains, and both are cheap compared with mechanical change. Neither replaces a heat sink, a fan, a thicker spreader or a better airflow route, and neither helps much on a surface that is already dark and matt. Where a customer sends us a thermal problem, we ask for the whole thermal budget first, because a coating can only act on the part of it that is a surface.

Every grade in this category is fixed against a measured number, so the specification starts as a development brief. The following are the questions we need answered before we can recommend a grade, and the answers usually come from the design engineer rather than from purchasing.

• What is the functional property and its limit? State the property, the value and the direction: surface resistivity between 1×10^6 and 1×10^9 ohms per square, dielectric withstand at a stated voltage and film thickness, thermal conductivity above a stated figure, emittance above a stated figure. A description such as anti-static or thermally conductive is not a specification.
• Which test method and which conditioning? Resistivity by ASTM D257 at a defined temperature and relative humidity, dielectric strength by IEC 60243-1 at a defined electrode and ramp rate, thermal conductivity by ASTM D5470, emittance by ASTM E408. The method changes the number, so both sides should agree it before samples are made.
• Is the requirement grounding or shielding? Bleeding off charge and attenuating a radiated field are different duties with different fills. If attenuation in decibels is required, state the frequency range and how the assembly will be measured, because a panel resistivity figure will not predict it.
• What is the substrate and its pre-treatment? Alloy or polymer grade, conversion coating or anodising, flame or plasma treatment, and whether the surface arrives cleaned, oiled or mould released.
• What film thickness can the design accept? Cell casings, connector fits, gasket compression and thermal interfaces all have dimensional limits, and thickness drives the electrical property directly.
• What is the service temperature range and cycling profile? Continuous maximum, peak excursion, low temperature limit and the number of cycles expected over life.
• What is the environment? Condensing humidity, salt, coolant, carbonate electrolyte, cleaning chemicals, ultraviolet exposure, and whether the part is indoor, enclosed or fully weather exposed.
• For conformal coatings, what is the rework policy? Whether boards are repaired in service or in the plant, and whether local removal and recoating is required. This decides acrylic against silicone before anything else. Where the duty is beyond both, vapour-deposited parylene is the alternative, and it is a vacuum process rather than a liquid coating.
• What is the application method and cure capability? Spray, dip, dip-spin, selective dispense, roller, curtain or coil, and the maximum bake temperature and dwell the assembled part can take. A coil-applied fluoropolymer and a sprayed one are different binders for this reason.
• What is the design life and the qualification programme? Twenty-five years outdoors for solar hardware, and the damp heat, thermal cycling, salt spray and weathering hours the part will be tested to.
• What volume and pack size, and in what form? Single component, two component with mix ratio and pot life, and whether the plant can handle a solvent-borne or only a water-borne product.

Compliance documentation, safety data sheets, a technical data sheet and a declaration covering the substances the customer restricts are issued on request against a named grade and a named application.

The Technical Data Sheet, Safety Data Sheet and regulatory declaration for any grade in this range are issued by our laboratory against the substrate and process you are running. Tell us the job and we will specify against it.