Outline
This method is used to repair 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.
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
Oven
General purpose oven for drying, baking and curing epoxies.
Scraper
Hardened stainless steel tip for scraping solder mask and removing defects.
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
Damaged hole, non plated.
Figure 1: Mill away damaged material with the Micro-Drill and ball mill.
Figure 2: Apply epoxy with a mixing stick sharpened at one end.
Figure 3: Micro-Drill System.
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 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.
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 prior to filling the area with epoxy. A preheated circuit 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.
Caution
Some components may be sensitive to high temperatures.
Mix the epoxy. If desired, add 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 epoxy cures.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
After the epoxy has cured, remove the tape.
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.
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.
