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3.5.1 Base Material Repair, Epoxy Method

Outline
This procedure is used to repair minor damage to circuit base board material. Scrapes and scratches in the base board material may be caused by accidents during handling. Burns in the base material may be caused by improper use of soldering and desoldering tools.

Caution
This method may be used when the damage extends deep into the base material, but not completely through. If the base board material is damaged completely through, see Procedure No. 3.5.2 or 3.5.3.

Caution
Surface circuits may need to be replaced in the damaged area. Be sure that the appropriate circuit diagrams, or photographs reflecting the original circuits are available so that they may be replaced after repairing the base board material. Damage to internal circuits or planes may have to be restored using surface wires.


Proprietary Information Proprietary
This guide may contain proprietary or copyright-protected information for access by authorized persons only.

Minimum Skill Level - Advanced
Recommended for technicians with soldering and component rework skills and exposure to most repair/rework procedures, but lacking extensive experience.

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  Proprietary
IPC-A-610 10.0 Laminate Conditions  Proprietary
Procedure References
1.0 Foreword
2.1 Handling Electronic Assemblies
2.2 Cleaning
2.5 Baking And Preheating
2.7 Epoxy Mixing and Handling
IPC7721 3.5.1 Base Material Repair, Epoxy Method
Tools and Materials
cutting
Ball Mills, Abrasives, Cutting Tools
Ball mills, abrasives and cutting tools for working on circuit boards.
Cleaner
Cleaner
General purpose cleaner for removing contamination.
235-2106-5
Cleaning Brushes
Disposable brushes for use with solvents for 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
Ideal for absorbing cleaning solvents, and applying color agents and epoxies.
235-3050
High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.
355-0614
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
Microscope
Microscope
Precision microscope with stand and lighting for work and inspection.
110-4105
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
115-3315-5
Mixing Picks
Unique mixing sticks have a paddle shape on one and sharp pick on the opposite end.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
335-3197
Scraper
Hardened stainless steel tip for scraping solder mask and removing defects.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
3.5.1 Base Material Repair, Epoxy Method
Damaged Base Material
3.5.1 Base Material Repair, Epoxy Method
Figure 1: Scrape away damaged base board material with a knife.
3.5.1 Base Material Repair, Epoxy Method
Figure 2: Micro-Drill System.

3.5.1 Base Material Repair, Epoxy Method
Figure 3: An undercut, to enhance mechanical strength, may be desired for class 3 product.
3.5.1 Base Material Repair, Epoxy Method
Figure 4: Apply the epoxy with a mixing stick sharpened at the end.
3.5.1 Base Material Repair, Epoxy Method
Figure 5: For large areas, apply the epoxy with a foam swab to create a texture.

3.5.1 Base Material Repair, Epoxy Method
Figure 6. Completed repair.
Procedure
  1. Clean the damaged area.
  2. Scrape away the damaged base board material using a knife. All damaged base board material and solder mask must be removed at the surface. (See Figure 1) or mill away the damaged base board material using the Micro-Drill System and ball mill. All damaged base board material and solder mask must be removed. (See Figure 2)

    Note
    To clearly see that all damaged material has been removed, flood the area with alcohol or solvent. Damaged internal fibers of the base material will show up clearly.

    Caution
    Abrasion operations can generate electrostatic charges.

    Note
    An undercut to enhance mechanical strength may be desired for class 3 product. (See figure 3)
  3. Remove all loose material and clean the area.
  4. Where needed, apply High Temperature tape to protect exposed parts of circuit board.

    Note
    The circuit Board may be preheated prior to filling the area with epoxy. A preheated PC board will allow the epoxy to easily flow and level out. Epoxy applied to an unheated circuit board may settle below the circuit board surface as the epoxy cures.
  5. Mix the epoxy. If desired, add color agent to the mixed epoxy to match the PC board color.
  6. Fill the area with epoxy up to and flush with the circuit board surface. No fibers of laminate material should be exposed. A mixing stick sharpened at the end may be used to apply and spread the epoxy. For large areas, apply the epoxy with a foam swab to create a texture in the surface. (See Figures 4 and 5)

    Note
    A slight overfill of epoxy may be desired to allow for shrinkage when epoxy cures.

    Note
    Epoxy may be applied using a foam swab to restore the surface appearance.
  7. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.

    Caution
    Some components may be sensitive to high temperature.
  8. After the epoxy has cured remove the tape.
  9. If needed, use a knife or scraper and scrape off any excess epoxy. Scrape until the new epoxy surface is level with the surrounding circuit board surface.
  10. Remove all loose material. Clean the area. (See Figure 6)

    Note
    If needed, apply an additional thin coating to seal any scraped areas.
Evaluation
  1. Visual examination for texture and color match.
  2. Electrical tests to conductors around the repaired area as applicable.
  3. No excess epoxy covering circuits or sensitive areas.
  4. Epoxy fully bonded. No evidence of chipping.
Procedure for reference only.