M78H-86 Polyurethane Conformal Coating for PCB Protection
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Short Product Description：
M78H-86 is a single-component polyurethane conformal coating designed for power PCBs and electronic assemblies requiring moisture protection. Its low-viscosity formulation supports brush, dip, and spray application, forming a glossy protective film through oxidative curing. It offers rapid touch drying, electrical insulation, and documented resistance to a 72-hour neutral salt spray test.
- Description
- Technical Data
- FAQ
Description
Product Overview：
M78H-86 is a solvent-based PCB conformal coating formulated with modified polyurethane resin, ester and hydrocarbon solvents, and specialty additives. It is intended for power circuit boards and electronic components where moisture protection, coating adhesion, and electrical insulation are important.
The single-component formulation cures by oxidation and does not require mixing separate resin and hardener components. At 25°C and 55% relative humidity, the coating becomes touch dry in 5–15 minutes. A short heating step at 60–80°C can accelerate initial drying, followed by room-temperature drying and continued property development.
Designed for a stated coating thickness of 25–50 μm, M78H-86 forms a glossy film with good film build and adhesion. The TDS reports dielectric withstand voltage above 1,500 V and insulation resistance above 1 × 10¹² Ω. It also reports no blistering, whitening, cracking, or rusting after 72 hours of neutral salt spray exposure under the specified conditions.
The stated use-temperature range is −40°C to +125°C. Final suitability should be verified on the actual assembly, considering material compatibility, coating coverage, environmental exposure, and completion of curing.
Key Features and Benefits：
· Single-Component Polyurethane Formulation: Simplifies preparation without a separate resin-to-hardener mixing ratio.
· Rapid Touch Drying: Reaches touch dryness in 5–15 minutes at 25°C and 55% RH, supporting handling once the coating condition has been verified.
· Optional Heat-Assisted Drying: A short exposure at 60–80°C accelerates initial drying. Further room-temperature drying is required for full property development.
· Low Application Viscosity: A specified Tu-4 cup viscosity of 12–18 seconds at 25°C supports brush, dip, and spray coating processes.
· Thin-Film PCB Protection: The TDS specifies a coating thickness of 25–50 μm for application development and coverage control.
· Electrical Insulation: Reports dielectric withstand voltage of >1,500 V and insulation resistance of >1 × 10¹² Ω.
· Moisture Protection: The TDS reports a moisture-resistance result of ≥5 × 10⁹ Ω, with MIL-46058C cited as the reference.
· Salt Spray Resistance: No blistering, whitening, cracking, or rusting was reported after 72 hours in 5% NaCl neutral salt spray at 35 ± 2°C.
· Adhesion and Gloss: Forms a glossy protective film with a reported adhesion classification of Grade 0–1.
· Temperature Resistance: The stated operating range of −40°C to +125°C supports evaluation for assemblies exposed to changing temperatures.
Typical Applications：
M78H-86 conformal coating is intended for:
· Power Printed Circuit Boards: Moisture protection of power electronics assemblies with demanding coating requirements.
· Electronic Components: Protective surface coating of compatible components and their connections.
· Electrical Assemblies: Insulation and moisture protection of suitable circuitry and associated parts.
· PCBs Exposed to Humidity or Salt-Laden Environments: Applications where the reported moisture and salt spray results provide a starting point for qualification.
· Brush, Dip, and Spray Coating Processes: Production methods requiring a low-viscosity polyurethane coating and ambient or heat-assisted drying.
Verify compatibility with solder mask, component markings, plastics, adhesives, and connectors before production use. Conformal coating does not establish an enclosure ingress-protection rating or replace application-specific environmental testing.
Physical Properties：
| Item | Specification | Test Method |
| Appearance | Yellowish-brown transparent liquid | Visual |
| Solid Content | 33±3% | — |
| Relative Density | 0.90±0.05 | — |
| Viscosity (25℃, Ford cup #4) | 12-18 s | — |
| Drying Time — 25℃, 55%RH | Tack-free: 5-15 min | — |
| Drying Time — 60-80℃ | Tack-free: ≤5 min | — |
| Recommended Drying | 60-80℃, 1-5 min + RT drying | — |
| Time to Best Performance | 7 days | — |
| Film Thickness | 25-50 μm | — |
| Adhesion | Grade 0-1 | — |
| Dielectric Withstand Voltage | >1500 V | MIL-46058C |
| Insulation Resistance | >10¹²Ω | MIL-46058C |
| Moisture Resistance | ≥5×10⁹Ω | MIL-46058C |
| Neutral Salt Spray (5% NaCl, 35±2℃, 72 h) | No blistering, whitening, cracking or rust | — |
| Flame Retardancy | Meets HB class | IPC-CC-830B |
| Operating Temperature | -40℃ to 125℃ | — |
| Recommended Thinners | X-86, X-86D | — |
Technical Notes:
· Viscosity is expressed as cup flow time in seconds.
· The TDS does not explicitly identify the 25–50 μm thickness as wet-film or dry-film thickness. Confirm the measurement basis before setting production limits.
· Dielectric withstand voltage in V is different from dielectric strength in kV/mm.
· Insulation resistance in Ω is different from volume resistivity in Ω·m or Ω·cm.
· Touch dryness does not indicate completion of curing or development of optimum properties.
Application Guidance：
· Production Environment
Provide effective extraction and maintain the following TDS-recommended application conditions:
· Ambient temperature: 10–30°C
· Relative humidity: below 75%
Keep the application area clean and control sources of contamination.
· Surface Preparation
Ensure the coating surface is dry, clean, and free from oil and foreign matter. Evaluate whether flux residues or other assembly contaminants require removal before coating.
The TDS states that special cleaning is not generally required, but cleanliness and compatibility must still be verified on the actual assembly.
Mask electrical contacts, connectors, test points, and other areas that must remain uncoated.
· Application and Thinning
Apply by brush, dip, or spray according to board geometry and production requirements. Use X-86 or X-86D thinner to adjust viscosity and coating thickness as needed.
Validate the dilution ratio, application settings, and coverage on the actual assembly. The TDS specifies 25–50 μm coating thickness, but its wet- or dry-film basis should be confirmed with the supplier.
Avoid pooling and unintended penetration into connectors or sensitive components.
· Drying and Curing
| Process Route | Reference Conditions | Important Follow-Up |
|---|---|---|
| Ambient drying | 25°C, 55% RH; touch dry in 5–15 min | Continue room-temperature drying; optimum properties are reported after 7 days |
| Heat-assisted drying | 60–80°C for 1–5 min | Continue room-temperature drying and validate final cure |
| Touch-dry reference under heating | 60–80°C; ≤5 min | Do not interpret as complete cure |
Set the heating temperature according to component temperature limits and production requirements. The TDS specifies a maximum baking temperature of 100°C.
Allow heated boards to cool before handling to avoid burns and damage to the film. Confirm complete drying and required performance before final electrical testing, packaging, or service.
· Container and Equipment Management
Keep coating containers closed whenever possible to limit moisture entry and solvent loss. Do not direct blowers at open containers; the TDS warns that this can accelerate evaporation or cause surface whitening.
During production interruptions, seal the coating supply and protect spray nozzles using the supplier-approved cleaning procedure. Clean lines and nozzles before extended shutdowns.
Store leftover working material separately in a sealed, compatible container. Do not mix used coating with fresh stock or return it to the original drum.
· Inspection and Rework
Inspect for coverage, adhesion, film thickness, and coating defects. The supplied TDS does not specify fluorescent inspection capability.
No cured-film removal procedure is provided. Confirm a compatible rework method with the supplier rather than assuming the application thinner will safely remove fully cured coating.
Precautions：
· Workplace control: good ventilation; temperature 10-30℃; humidity <75%.
· Board cleaning: generally no special cleaning is required; ensure the coated surface is dry, clean, and free of oil and impurities.
· Suitable for brushing, dipping and spraying. A single coat is generally 25-50 μm; adjust viscosity and film thickness with thinner to best suit your process.
· Keep the container sealed during use to prevent moisture ingress. Do not blow air directly at the open container, to avoid solvent evaporation or surface whitening.
· If production pauses, seal the container and soak the nozzle in cleaning agent to prevent clogging.
· Baking temperature depends on component heat resistance and process, max 100℃. Do not touch freshly baked products until cooled, to avoid burns or film damage.
· Unused coating should be stored sealed in a dedicated container; do not mix it with fresh coating.
· If unused for long, clean pipes and nozzles; pour the coating out and store sealed; do not return used product to the original pail.
· Used containers, pipes and nozzles can be cleaned with thinner.
Packaging, Storage/Transport & Shelf Life：
· Packaging: metal pails, 4 KG/pail, 20 KG/pail
· Storage & transport: flammable chemical — keep away from fire and heat; handle per regulations; store cool (RT), dark and dry.
· Shelf life: stored sealed, 6 months at 5-25℃.
Conformal Coatings：
Thinners：
Frequently Asked Questions About M78H-86 Conformal Coating
1. What is M78H-86 conformal coating used for?
M78H-86 is a solvent-based, modified polyurethane conformal coating designed for power printed circuit boards, electronic components, and compatible electrical assemblies.
It forms a glossy protective film that provides adhesion, electrical insulation, and moisture protection. Applications include electronics exposed to humidity or salt-laden environments, subject to testing on the actual assembly.
2. Does M78H-86 require a separate hardener?
No. M78H-86 is a single-component coating that cures by oxidation. It does not require a separate resin-to-hardener mixing step.
If viscosity adjustment is needed, use the specified X-86 or X-86D thinner according to the supplier’s instructions. Validate the dilution ratio and drying process before production use.
3. How long does M78H-86 take to dry at room temperature?
At 25°C and 55% relative humidity, M78H-86 reaches touch dryness in 5–15 minutes. The TDS reports optimum properties after seven days.
Touch dryness does not mean complete curing. Actual property development depends on film thickness, airflow, environmental conditions, and coating retained around components. Confirm the required performance before final testing, packaging, or service.
4. Can M78H-86 drying be accelerated with heat?
Yes. The recommended heat-assisted route is 60–80°C for one to five minutes, followed by continued room-temperature drying.
This short heating step accelerates initial drying but does not establish complete cure. The TDS specifies a maximum baking temperature of 100°C. Select a temperature compatible with all board components and allow heated assemblies to cool before handling.
5. Can M78H-86 be brushed, dipped, or sprayed?
Yes. M78H-86 supports brush, dip, and spray application. Select the method according to board geometry, masking requirements, and production volume.
Validate wetting and coverage on representative assemblies. Avoid pooling and unwanted entry into connectors, contacts, sensors, or other areas that must remain uncoated.
6. What coating thickness is recommended for M78H-86?
The TDS specifies a coating thickness of 25–50 μm but does not explicitly identify it as wet-film or dry-film thickness.
Confirm the measurement basis with the supplier before establishing production limits. Validate thickness and coverage around component edges, leads, and other difficult-to-coat areas.
7. Which thinner should be used with M78H-86?
Use X-86 or X-86D thinner to adjust M78H-86’s application viscosity and coating thickness.
The supplied data reports a cup flow time of 12–18 seconds at 25°C. Confirm the applicable cup method before using this value for process control. Determine thinner addition through trials rather than assuming one dilution ratio suits brushing, dipping, and spraying.
8. Do PCBs need cleaning before applying M78H-86?
PCB surfaces must be dry, clean, and free of oil and foreign matter. Although the TDS states that special cleaning is not generally required, flux residues and other contaminants still need evaluation for adhesion and compatibility.
Verify compatibility with solder mask, component markings, plastics, and adhesives. Mask electrical contacts, connectors, and test points before coating.
9. What temperature and humidity are recommended during application?
The TDS recommends an application temperature of 10–30°C and relative humidity below 75%, with effective ventilation and extraction.
Keep containers closed whenever possible to limit moisture entry and solvent loss. Avoid directing blowers at open containers, as the TDS warns this can accelerate evaporation or cause surface whitening.
10. What electrical insulation performance does M78H-86 provide?
The TDS reports dielectric withstand voltage greater than 1,500 V and insulation resistance greater than 1 × 10¹² Ω. It also reports a moisture-resistance result of at least 5 × 10⁹ Ω.
The withstand-voltage result is not dielectric strength in kV/mm or a finished-board operating-voltage rating. Assembly design, coverage, film thickness, and complete curing must also be evaluated.
11. How does M78H-86 perform in salt-spray environments?
The TDS reports no blistering, whitening, cracking, or rusting after 72 hours of neutral salt-spray exposure using 5% NaCl at 35 ± 2°C.
This result supports evaluation for salt-exposed applications but does not establish a service-life prediction, waterproof rating, or enclosure ingress-protection rating. Validate performance on the actual coated assembly.
12. What is the operating temperature range of M78H-86?
The stated operating temperature range is −40°C to +125°C.
Confirm suitability for the actual exposure duration, thermal cycling, component materials, and coating condition. This service-temperature range is separate from the maximum baking temperature of 100°C specified for processing.
13. Does M78H-86 support fluorescent inspection or coating removal for repair?
The supplied TDS does not specify fluorescent inspection capability. Use a validated method to inspect coverage, thickness, adhesion, and defects.
A cured-film removal procedure is also not provided. Confirm a compatible rework method with the supplier rather than assuming X-86 or X-86D application thinner will safely remove fully cured coating.
14. What safety and compliance documents are available for M78H-86?
The Conformal Coatings downloads section lists an MSDS, RoHS documentation, REACH documentation, and UL documentation. Request the documents applicable to M78H-86 and review their product coverage, dates, and stated scope.
For UL details, refer to the applicable document for the exact recognition or classification and conditions of use. The Thinners section separately lists RoHS documentation and a halogen content test report.
15. How is M78H-86 packaged and stored?
M78H-86 is supplied in 4 kg and 20 kg metal pails. Its stated shelf life is six months when stored sealed at 5–25°C.
Store it in a cool, dark, dry location away from fire and heat sources, following the current MSDS. Keep used working material separate from fresh stock and do not return it to the original container.
16. What information should I provide when requesting an M78H-86 quotation?
Include your PCB or assembly type, application method, target coating thickness, available drying conditions, and required environmental and electrical performance.
For pricing and delivery, provide the required quantity, preferred pack size, destination, target delivery date, and any requirements for thinner, trial material, or supporting documents.
