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2.4.1 Coating Replacement, Solder Mask

 
Outline
This method is used to replace solder masks 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
Kits and Systems
201-2100
Professional Repair Kit
Kit to repair circuit board damage including pads, lands, conductors, base material and plated holes.
201-2400
Master Repair Kit
Kit to repair circuit board damage including pads, lands, conductors and base material.
201-3110
Base Board Repair Kit
Kit to repair base board and laminate damage on circuit boards.
115-1322
Circuit Bond Kit
Includes packages of clear, low viscosity, superior strength epoxy for circuit board damage repair.
201-4350
Repair Skills Practice Kit
Training kit to practice circuit board repair skills prior to testing for certification.
201-7100
Precision Tool Set
Nine precision-crafted tools for detailed circuit board work.
Tools and Materials
235-2106-5
Cleaning Brushes
Disposable brushes for solvent cleaning and application of coatings.
Coatings
Color Agents
Use to tint the color of epoxy used for solder mask repair or circuit base board repair.
115-3302
Circuit Bond Epoxy
Clear, superior strength epoxy in two-compartment plastic packages.
235-2102-5
Foam Swab, Small
Swabs for use with solvents and application of color agents and epoxies.
Additional Items and Supplies
Cleaner
Cleaner
General purpose cleaner for removing contamination.
Coatings
Coatings
Replacement soldermask and conformal coatings.
Microscope
Microscope
Precision microscope with stand and lighting for work and inspection.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Circuit Bond Epoxy
Circuit Bond is a clear, low viscosity, superior strength epoxy precisely measured out into two-compartment plastic packages, so it's easy to use, and there's no measuring. For over a decade, this high-strength epoxy has been qualified and used by thousands of high-rel electronics manufacturers across the globe.
1. Circuit Bond has a working pot life of 30 minutes. It should not be mixed until ready to use.
2. To use Circuit Bond, remove the plastic clip separating the resin and hardener. Squeeze back and forth from one half of the package to the other to mix the contents.
3. Cut a corner off the package and squeeze all the contents into a Plastic Cup. Stir the contents to ensure it is thoroughly mixed.
4. Circuit Bond may contain bubbles from the mixing process. If needed, use a vacuum system to remove bubbles.
5. Color Agent can be mixed in with Circuit Bond to match surface colors if desired.
6. Apply using a Foam Swab, Micro Probe, or Mixing Stick as required.
7. Cure Circuit Bond for 24 hours at room temperature or 4 hours at 65°C (150°F).
Specifications
Packaging2 gram pre-measured packages
Mix ratio4 parts resin to 1 part hardener
Mix Ratio by Weight (R/H)100/25
ColorClear, transparent
Pot life30 minutes
Cure cycle24 hours at room temp (25 °C) or 4 hours @ 65°C
Thixotropic Index1
Specific Gravity1.20
Percent Solids100%
Viscosity (after mixing)2000 cps
Operating temperature range-55°C to 135°C
Hardness88 Shore D
Lap Shear, Alum to Alum1100 psi
Glass Transition Temperature, Ultimate92°C
Coefficient of Expansion, cm/cm/°C6 E-05
Dielectric strength400 volts/mil
Dielectric Constant, 1KHz@25°C4
Shelf Life6 months minimum
Color Agents
Color Agent is a one-part, air-drying, semi-paste ink commonly used to print hard surfaces, including circuit board base materials. Color Agent can be used to tint the color of epoxy used for solder mask repair or circuit baseboard repair. To use, mix a small amount of color agent with 2 part epoxy as the epoxy is initially mixed. Add more color agents to increase the color intensity if needed.
Part No. Description
115-9102 115-9102 Color Agent, Yellow
115-9185 115-9185 Color Agent, Red
115-9293 115-9293 Color Agent, Blue
115-9348 115-9348 Color Agent, Green
115-9358 115-9358 Color Agent, Light Green
115-9376 115-9376 Color Agent, Medium Green
115-9424 115-9424 Color Agent, Dark Gray
115-9457 115-9457 Color Agent, Light Brown
115-9560 115-9560 Color Agent, Dark Green
115-9561 115-9561 Color Agent, Green
115-9995 115-9995 Color Agent, Black
115-9996 115-9996 Color Agent - White
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 High-Temperature Tape to outline the area where the solder mask will be applied.
  3. Mix the epoxy or replacement coating. If desired, add a 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 temperatures.
Evaluation
  1. Visual examination for texture, color match, adhesion, and coverage.
  2. Electrical tests to conductors around the repaired area as applicable.
Procedure for reference only.