Circuit Technology Center
 
No. 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.

ACCEPTABILITY REFERENCES
IPC-A-600 2.0 Externally Observable Characteristics
IPC-A-610 10.0 Laminate Conditions
 
PROCEDURE REFERENCE
CTC 7721 1.0 Foreword
CTC 7721 2.1 Handling Electronic Assemblies
CTC 7721 2.2 Cleaning
CTC 7721 2.3.1 Coating Removal, Identification Of Coatings
CTC 7721 2.4.2 Coating Replacement, Conformal Coatings/Encapsulants
CTC 7721 2.5 Baking and Preheating
CTC 7721 2.7 Epoxy Mixing and Handling
IPC 7721 2.4.1 Coating Replacement, Solder Resist

TOOLS & MATERIALS
Brushes
Cleaner
Color Agents
Epoxy
Foam Swabs
Heat Lamp
Microscope
Oven
Replacement Coating
Wipes

PROCEDURE

  1. Clean the area.

    2. 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.

    6. 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.
 		  
Solutions Across the Board TM

Product Class:  R/F/W/C
Skill Level:  Intermediate
Conformance Level:  High
Revision:  D
Revision Date:  Jan 5, 1998
Repair Service Charge

Soldermask Required At Outlined Area

Figure 1: For large surfaces, apply the replacement coating with a foam swab to create a texture.
Tricks of the Trade
 There are too many solder mask and solder resist materials on the market to have replacements in stock and on hand when they're needed. We use a simple-to-use replacement Epoxy for nearly all solder mask and solder resist repairs. This high strength, clear Epoxy is supplied in a unique 2 part package. You'll always have the exact ratio of hardener and resin. We normally mix in a Color Agent with the epoxy or may apply the Color Agent directly to the board surface to match the surface color. We often apply the material with a foam swab to match the surface texture. Sounds simple, but this is art. Matching colors and textures precisely requires experience
 
 
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