3.3.1 Hole Repair, Epoxy Method

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Outline

This method repairs cosmetic defects or minor damage to an unsupported tooling or mounting hole. The hole may have component leads, wires, fasteners, pins, terminals, or other hardware run through it. This repair method uses high-strength epoxy to restore the damaged surface surrounding the hole. This method can be used on single-sided, double-sided, or multilayer circuit boards and assemblies.

Caution: Damaged inner-layer connections may require surface wire adds.

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.

Procedure References
1-0	1.0 Foreword
2-1	2.1 Handling Electronic Assemblies
2-2	2.2 Cleaning Procedures
2-5	2.5 Baking and Preheating
2-7	2.7 Epoxy Mixing and Handling

Tools and Materials

Ball Mills, Abrasives, Cutting Tools
Ball mills, abrasives and cutting tools for working on circuit boards.

Circuit Bond Epoxy
Clear, superior strength epoxy in two-compartment plastic packages.

Cleaner
General purpose cleaner for removing contamination.

Cleaning Brushes
Disposable brushes for solvent cleaning and application of coatings.

Color Agents
One part, semi-paste ink used to tint the color of epoxy and for direct printing on circuit board surfaces.

Flex-Rack PCB Holder
Sturdy rack for PCBs used for rework and positioning.

High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.

Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.

Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding.

Oven
General purpose oven for drying, baking and curing epoxies.

Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.

Wipes
Nonabrasive, low-linting wipes for cleanup.

Procedure

Clean the area.
Mill away the damaged board base material using the Micro-Drill and ball mill. All damaged base board material and solder mask must be removed. No fibers of laminate material should be exposed at the surface perimeter of the hole. (See Figure 1)
Note: To 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.
Remove all loose material and clean the area.
Where needed, apply High-Temperature Tape to protect exposed parts of the circuit board. Tape may be required inside the hole. If epoxy reduces the inside diameter, the hole may have to be re-drilled after the epoxy has cured.
Note: The circuit board may be preheated before filling the area with epoxy. A preheated circuit board allows the epoxy to flow and level out easily. Epoxy applied to an unheated circuit board may settle below the circuit board surface as the epoxy cures.
Caution: Some components may be sensitive to high temperatures.
Mix the epoxy. If desired, add a color agent to the mixed epoxy to match the circuit board color.
Coat the area with epoxy up to and flush with the circuit board surface. A mixing stick may be used to apply and spread the epoxy.
Note: A slight overfill of epoxy may be desired to allow for shrinkage when the epoxy cures.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
After the epoxy has cured, remove the tape.
Use a knife or scraper to scrape off any excess epoxy if needed. Scrape until the new epoxy surface is level with the surrounding circuit board surface.
Note: Apply surface coating to match prior coating as required.
Remove all loose material. Clean the area.

Evaluation

Visual and dimensional examination of the reworked area for conformance to drawings and specifications.

Images

Hole Repair, Epoxy Method

Damaged non-plated hole.

Mill away the damaged board base material using the Micro-Drill and ball mill.

Mix the epoxy. If desired, add a color agent. Coat the area with epoxy up to and flush with the circuit board surface.