M78H-41 Polyurethane Conformal Coating for PCB Protection

Description

Product Overview：

M78H-41 is a solvent-based PCB conformal coating formulated with modified polyurethane, water-repellent additives, and specialty additives. It is designed to protect compatible surfaces against moisture and water exposure while providing electrical insulation.

After drying, M78H-41 forms a transparent, glossy film with strong adhesion. Its hydrophobic surface helps limit wetting, making the coating relevant to electronic assemblies exposed to humidity and temperature changes. Actual protection depends on surface preparation, continuous coverage, coating thickness, and complete drying.

The TDS reports insulation resistance above 2.5 × 10¹² Ω and a moisture-resistance test result of at least 5 × 10⁹ Ω. It also describes resistance to acids, alkalis, and impurity-containing water, together with a passing anti-sulfurization test result.

M78H-41 can be used as supplied or adjusted with the dedicated X-4H thinner. Its single-component format and choice of ambient or oven drying support straightforward integration into a validated coating process.

  · Hydrophobic Surface Protection: Forms a water-repellent film designed to limit surface wetting and support moisture protection.

  · High Insulation Resistance: The TDS reports insulation resistance of >2.5 × 10¹² Ω, providing a reference for electrical insulation performance.

  · Moisture Resistance: A reported moisture-test resistance of ≥5 × 10⁹ Ω supports evaluation for humidity-exposed assemblies.

  · Single-Component Polyurethane Formulation: Simplifies preparation without mixing separate resin and hardener components.

  · Transparent, Glossy Finish: Allows underlying surfaces and markings to remain visible while providing a protective film.

  · Strong Adhesion: Bonds to compatible, properly prepared surfaces to support coating continuity.

  · Ambient or Oven Drying: Reaches surface dryness in ≤30 minutes at room temperature and 55% RH, with an alternative full-drying schedule of 2 hours at 80°C.

  · Anti-Sulfurization Performance: The TDS reports a passing result. Suitability for a particular sulfur-containing atmosphere requires application-specific testing.

  · Chemical Resistance: Described as resistant to acids, alkalis, and impurity-containing water. Confirm resistance to the actual chemicals, concentrations, temperatures, and exposure periods involved.

  · Defined Application Thickness: The TDS specifies a coating thickness of 30–50 μm for process development.

Typical Applications：

M78H-41 conformal coating is intended for:

  · Printed Circuit Boards: Moisture protection and electrical insulation of compatible PCB assemblies.

  · Electronic Components: Protective coating of suitable component surfaces and associated circuitry.

  · Metal Surfaces: Water-repellent and moisture-protective surface treatment.

  · Humidity-Exposed Electrical Assemblies: Applications requiring a transparent protective film with high insulation resistance.

  · Assemblies Requiring Anti-Sulfurization Evaluation: Applications where the TDS’s reported passing result can serve as a starting point for qualification.

The TDS identifies use in both high- and low-voltage equipment. However, equipment suitability must be established from the complete design; the coating’s reported withstand-voltage value is not a finished-equipment voltage rating.

Physical Properties：

Technical Notes:

  · Viscosity is expressed as cup flow time in seconds.

  · 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：

  · Surface Preparation

Ensure surfaces are dry and free from oil, dust, and contamination that could affect adhesion, wetting, or electrical performance.

Assess flux residues and other soldering contaminants before coating. Remove residues where their compatibility or electrical behavior has not been established.

Mask contacts, connectors, test points, and other areas that must remain uncoated.

  · Preparation and Thinning

M78H-41 may be used as supplied. When viscosity adjustment is required, use only the dedicated X-4H thinner according to the supplier’s instructions.

The TDS warns that unsuitable thinners may cause precipitation, separation, or unwanted polymerization. Determine the dilution ratio through application trials rather than using a general-purpose solvent.

  · Application and Thickness Control

Brush coating is described in the TDS, and the MSDS also identifies spray application. Validate the selected process using the actual board geometry and equipment.

For brushing, dispense small amounts frequently to limit exposure of the working material to air and moisture.

Use the stated 30–50 μm coating thickness as a starting point, after confirming whether it refers to wet or dry film. Inspect for continuous coverage, missed areas, pooling, and unwanted penetration into sensitive components.

  · Drying Conditions

These are reference conditions. Actual drying depends on coating thickness, retained solvent, airflow, assembly geometry, and oven loading.

Confirm component compatibility with the selected baking temperature. Allow the assembly to dry completely before final electrical testing, packaging, or service.

  · Working-Material Control

Solvent evaporation from an open container can increase viscosity and relative density, making application less consistent and affecting film formation.

Monitor the working coating and replenish X-4H thinner according to the validated process. Protect the material from moisture, which the TDS identifies as a cause of gelation or clumping.

During extended interruptions, transfer working material to a suitable sealed container rather than leaving it exposed.

  · Use with Soldering Residues

The TDS describes a limited remedial use with certain low-rosin or low-solids flux residues. Treat this as a supplier-qualified application, not a general substitute for cleaning.

Confirm compatibility with the exact flux and validate adhesion and electrical reliability before adoption. The TDS states that higher-residue surfaces should be cleaned before coating.

  · Inspection and Rework

Inspect coating continuity, thickness, adhesion, and drying. Fluorescent inspection capability is not specified in the supplied documents.

No cured-film removal procedure is provided. Confirm a compatible rework method with the supplier; do not assume that X-4H thinner is suitable for removing fully dried coating from every assembly.

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 30-50 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: 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℃.