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2.4.1 Coating Replacement, Solder Mask
Outline
This method is used to replace solder mask or coatings on circuit boards. Most replacement coatings can be applied by dipping, brushing or spraying.
Minimum Skill Level - Intermediate
Recommended for technicians with skills in basic soldering and component rework, but may be inexperienced in general repair/rework procedures.
Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.
Acceptability References
IPC-A-600 2.0 Externally Observable Characteristics
IPC-A-610 10.0 Laminate Conditions
Procedure References
1.0 Foreword
2.1 Handling Electronic Assemblies
2.2 Cleaning
2.3.1 Coating Removal, Identification Of Coatings
2.4.2 Coating Replacement, Conformal Coatings/Encapsulants
2.5 Baking and Preheating
2.7 Epoxy Mixing and Handling
IPC7721 2.4.1 Coating Replacement, Solder Resist
Tools and Materials
Cleaner
Cleaner
General purpose cleaner for removing contamination.
115-9000 Color Agents
Coatings
Replacement soldermask and conformal coatings.
CircuitMedic Part
Epoxy Kit
High temperature epoxy for masking and structural repairs to circuit boards.
Microscope
Microscope
It is a challenge to undertake precision repair without a good microscope.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
2.4.1 Coating Replacement, Solder Mask
Soldermask Required At Outlined Area
2.4.1 Coating Replacement, Solder Mask
Figure 1: For large surfaces, apply the replacement coating with a foam swab to create a texture.
Procedure 
  1. Clean the area.

    Caution
    Surfaces to be coated must be thoroughly cleaned prior to coating to ensure adequate adhesion, minimized corrosion, and optimized electrical properties.

  2. If needed, apply Kapton tape to outline the area where the soldermask will be applied.

  3. Mix the epoxy or replacement coating. If desired, add color agent to the mixed epoxy to match the circuit board color.

  4. Apply the replacement coating to the board surface as required. A brush or foam swab may be used to apply and spread the epoxy or replacement coating. (See Figure 1).

  5. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.

    Caution
    Some components may be sensitive to high temperature.

Evaluation

  1. Visual examination for texture, color match, adhesion and coverage

  2. Electrical tests to conductors around the repaired area as applicable.

This procedure is for reference only. Refer to the Procedure References listed above, or contact Circuit Technology Center for appropriate industry approved references.
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CircuitMedic
22 Parkridge Road, Haverhill, MA 01835 USA
Phone: 978-373-1600 - Fax: 978-372-5700
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