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Specify dry film thickness and the place it applies

Conformal coating thickness usually refers to the cured protective film on an electronic assembly. A useful specification identifies the coating product, dry-film range, required coverage, keep-out regions, cure condition and measurement method. A thickness number without those details is difficult to manufacture consistently and even harder to inspect fairly.

Liquid wet-film thickness is a different quantity. Solvent or water leaves during drying, while curing may introduce other changes. A wet reading therefore cannot be treated as a final dry reading. Equally, a measurement on a convenient flat coupon does not automatically represent the film at a sharp lead, a board edge or a shadowed region under a component.

A thickness callout is part of a complete coating drawing

HumiSeal's gives 25鈥�75 碌m as a common dry-film range for many acrylic, urethane and silicone products and 5鈥�25 碌m for parylene. These are supplier-published orientation ranges, not a universal acceptance table. The current product data sheet and agreed assembly requirement determine the actual limits; some systems require a different thickness.

A thicker coating is not automatically a better coating. Excess film can affect cure, flexibility, stress, heat dissipation and serviceability. A thin region may fail the coverage or protection objective. The appropriate balance depends on the actual material and environment. Do not increase thickness simply to compensate for inadequate cleaning, an uncontrolled application process or an undefined qualification requirement.

Translate a dry target into a liquid-film planning range

The worksheet uses a simple volume balance: dry thickness is approximately wet thickness multiplied by volume-solids fraction. Enter the dry limits and the volume-solids content of the material as applied, including any approved dilution. Weight-percent solids is not interchangeable with volume-percent solids. If only weight data are available, obtain the appropriate product information instead of substituting the number.

For an illustrative 30鈥�60 碌m dry target and 40% volume solids, the ideal wet-film interval is 75鈥�150 碌m. A measured 100 碌m wet film would correspond to an ideal 40 碌m dry film under the model. This example is arithmetic, not a named coating recipe. Real deposition, flow, cure and surface geometry must be checked with dry-film measurements for the selected product.

The optional reading list compares measured dry-film values with your entered dry limits and reports individual out-of-window readings. It does not decide whether the board passes an acceptance standard. Your sampling plan, instrument uncertainty, allowed exceptions and decision rule remain part of the project agreement. Use labelled measurement locations in the production record even when the quick worksheet contains only numeric readings.

Match the measurement method to the surface

Wet-film gauges are useful process aids when the surface and coating permit them, but they may disturb the film. A measurement should not damage a finished critical region simply because it is convenient. Use an approved witness area or coupon where appropriate, and define whether the measurement occurs before material has flowed or solvent has begun to leave.

Dry-film methods must suit the substrate and film. A differential measurement compares coated and uncoated thickness under controlled conditions; an instrument-based method needs an appropriate measurement principle and calibration. Cross-section analysis can reveal a local film profile but is destructive and highly location-specific. Select the method with the coating supplier and inspection engineer instead of assuming any general paint gauge works on a populated PCB.

Fluorescence helps reveal where a compatible coating has been applied and can make certain coverage defects visible. Brightness is influenced by the material, illumination, viewing conditions and geometry. It is not, by itself, a calibrated thickness measurement. A photograph with a bright coating region should not be presented as proof that the dry film meets a numerical limit.

Inspect the difficult regions, not just the average

Coating can collect at component bases and recede from sharp edges. The same assembly may contain a thick pool, a thin lead edge and an acceptable flat area. An average of selected readings can hide those differences. The drawing should identify the regions that need quantitative measurements and those assessed by a specified coverage or workmanship criterion.

Suppose five illustrative readings are 29, 35, 42, 48 and 61 碌m against a 30鈥�60 碌m requirement. Their average is 43 碌m, which lies inside the interval, but two individual readings are outside it. Whether those positions constitute a reject depends on the specified measurement locations and acceptance rule. The worksheet deliberately reports the outliers instead of converting the average into a reassuring pass badge.

Record instrument resolution and uncertainty, coupon material, surface condition and cure state. Readings near a limit may need an agreed guard band or another decision rule. Do not silently round a value into compliance. Keep the measurement plan consistent across prototype and repeat orders so apparent process changes are not caused by a new measurement method or location.

Thickness control starts before application

Cleanliness and compatibility matter before the first coat is applied. Flux residues, handling contamination and incompatible materials can affect adhesion or protection. 鈥淣o-clean鈥� identifies a soldering-material/process context; it does not automatically establish compatibility with every coating or service environment. Agree the necessary cleaning and drying route for the actual assembly and coating system.

Application variables include viscosity at a stated temperature, approved thinner ratio, dispense or spray settings, travel path, number of passes and time between stages. Keep-outs require a defined masking method and removal sequence. A fixture that changes the board angle can also change flow or access. Record meaningful process conditions so a qualified result can be reproduced rather than relying on a final appearance check alone.

Electrolube's is an example of product-specific application and dilution guidance. Its instructions belong to that product, not every acrylic coating. Use the selected material's current technical and processing documents for actual curing and handling. A broad chemistry name such as acrylic or silicone is not enough to establish all process settings.

Distinguish material qualification from assembly acceptance

IPC-CC-830 addresses insulating-compound qualification and performance for printed wiring assemblies. IPC-A-610 addresses assembly acceptability, while applicable process requirements may also be defined by J-STD-001 and the contractual drawing. Their roles are different. A coating material's qualification does not prove that a specific assembly has been cleaned, masked, coated and cured correctly.

Use the to identify the relevant documents and current revision, then state which requirements apply to the purchase. The 吃瓜tv assembly standards guide helps organize that conversation. Do not combine a material certificate, a generic thickness range and a class label into an unsupported claim of total compliance.

Conformal coating also does not automatically make a product waterproof, hermetic or suitable for a safety-critical environment. Required electrical, moisture, corrosion, temperature-cycle or other qualification evidence depends on the complete design. An application-specific evaluation should include connectors, enclosure features and uncoated areas, not only the polymer film on a flat test coupon.

Quote coverage, masking and inspection together

Coating cost includes more than the material volume. Preparation, cleaning, masking, application, cure time, inspection, records and rework can dominate a small or complex build. Two assemblies with equal coated area can require very different effort if one has many connectors, sensitive openings or tight keep-out boundaries. Supply the marked coverage drawing when asking for a price.

Separate one-time programming and fixture work from recurring operations. State whether both sides are coated, how tests are sequenced, whether access points remain available and whether repaired boards need a special acceptance route. Do not assume the lowest liquid-material price gives the lowest accepted-assembly cost. A proper comparison includes the complete process and required verification.

For a broader manufacturing program, coordinate coating with electronic contract manufacturing. The required PCBA files guide covers the base release package; add coating product, coverage, dry-film limits, cure instructions, inspection plan and environmental requirements. Unresolved chemistry or thickness choices can be included as engineering questions in the enquiry.

Coating thickness questions