3.4.1 Key and Slot Repair, Epoxy Method

Outline

This method repairs minor damage to a key slot or other cutout in a printed board or assembly. The area is repaired using high-strength epoxy.

Caution: Care should be taken to limit the application of epoxy to the specific areas desired and to avoid damaging the conductive patterns, contacts, and components.

Minimum Skill Level - Advanced

Conformance Level - High

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.

Micro Probes Sharp probes for dispensing adhesive and positioning small objects.

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

Precision Tool Set Nine precision-crafted tools for detailed circuit board work.

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

Wipes Nonabrasive, low-linting wipes for cleanup.

Procedure

1. Clean the area to be filled, including the edges.
2. Mill away the damaged board base material using a micro-drill system and ball mill. All damaged base board material must be removed. No fibers of laminate material should be exposed at the surface of the key slot. (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. 
   Caution: Abrasion operations can generate electrostatic charges.
3. Remove all loose material and clean the area.
4. Apply high-temperature tape to the circuit board's surface adjacent to the slot. The tape should protect any adjacent contacts or components.
   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.
5. Mix the epoxy. If desired, add a color agent to the mixed epoxy to match the circuit board color.
6. Apply a small amount of epoxy to the edges of the slot. A mixing stick sharpened at the end or a micro-probe may be used. (See Figure 2) 
   Note: A slight overfill of epoxy may be desired to allow for shrinkage when the epoxy cures.
   Note: The circuit board may be turned on its side to keep the epoxy in place while it cures.
7. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
   Caution: Some components may be sensitive to high temperatures.
8. After the epoxy has cured, remove the tape.
9. Use a knife or scraper to scrape off any excess epoxy if needed.
10. If precision is required, machine the edges of the slot using a milling machine or precision drill system and an appropriate milling cutter. Use great care to relocate the slot correctly. 
    Note: If needed, apply a thin coating to seal scraped areas.
11. Clean the area.

Evaluation

1. Visual examination and measurement of the key slot location and dimension.

Images

Key and Slot Repair, Epoxy Method

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

Apply epoxy to the edges of the key slot using a mixing stick or micro-probe.

Completed key slot repair.