3.4.2 Key and Slot Repair, Transplant Method

Outline

This method modifies or repairs a key slot or other cutout in a printed board or assembly. A replacement piece of matching board material is epoxied into the area needing repair. If needed, a new cut is machined into the repaired area.

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

Minimum Skill Level - Expert

Conformance Level - High

Tools and Materials

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.

End Mills Designed for end cutting and hole boring.

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.

Milling Machine Use for precision milling of circuit board materials.

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

Precision Drill Precision drill press for accuracy and controlled depth drilling.

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 out the damaged area using a milling machine or Precision Drill System and a carbide end mill. (See Figure 1)
3. Clean the area.
4. Install the carbide saw into the Micro-Drill System. Set the speed to maximum and machine a groove in the edge of the circuit board where the new base material will be installed. The groove must be centered on the edge to ensure the new piece fits properly. The groove width should be approximately 1/3 of the circuit board thickness. The groove depth should be approximately double the groove width. (See Figure 2)
5. Cut a piece of replacement baseboard material that is the same thickness and type as the circuit board. The replacement piece should be longer than the slot to allow for ease of handling. 
   Install an end mill into the milling machine. Machine a tongue onto both sides of the replacement piece. The dimensions of the tongue should match the size of the milled groove. (See Figure 3)
6. Where required, apply High-Temperature Tape to protect exposed parts of the circuit board bordering the prepared area.
7. Carefully check the fit of the replacement piece, then clean it and the slot. The replacement base material should fit firmly into the slot so it will not move or fall out when epoxied.
8. Apply High-Temperature Tape to the surface of the circuit board adjacent to the slot. The tape should protect any adjacent contacts or components.
9. Mix the epoxy.
10. Apply a small amount of epoxy to the edges of the replacement piece and the inside edges of the slot.
11. Insert the replacement piece into the slot. Check alignment. Remove excess epoxy. (See Figure 3)
12. If needed, apply additional epoxy to the slot edges. A mixing stick sharpened at the end may be used to apply the epoxy.
13. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
    Caution: Some components may be sensitive to high temperatures.
14. After the epoxy has cured, remove the tape.
15. Use a knife or scraper to scrape off any excess epoxy if needed. 
    Note: If needed, apply an additional thin coating to seal any scraped areas.
16. Cut off the excess length of replacement material and file to match the contour of the existing edge. (See Figure 4)
17. If a new slot is needed, machine it using a milling machine and an appropriate milling cutter. Take great care to relocate the slot correctly.
18. Clean the area.

Evaluation

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

Images

Key and Slot Repair, Transplant Method

Mill out the damaged area using a milling machine or Precision Drill System.

Cut a groove into both sides of the key slot using a Micro-Drill System and carbide saw.

Insert the replacement piece into the slot.

Cut off excess material and file to match edge.