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3.4.2 Key and Slot Repair, Transplant Method
Outline
This method is used to modify or repair 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. A new cut is then machined into the repaired area if needed.

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
Recommended for technicians with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.

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
IPC-A-610 10.0 Laminate Conditions
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 3.4.2 Key and Slot Repair, Transplant Method
Tools and Materials
CircuitMedic Part
Alcohol Swab
Self-saturating Isopropyl alcohol swab. Squeeze handle to release alcohol.
Cleaner
Cleaner
General purpose cleaner for removing contamination.
CircuitMedic Part
Cleaning Brushes
Disposable brushes for use with solvents for cleaning and application of coatings.
End Mills
End Mills
Designed for end cutting and hole boring.
CircuitMedic Part
Circuit Bond Packs
Clear, superior strength epoxy in two-compartment plastic packages
CircuitMedic Part
High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.
CircuitMedic Part
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
CircuitMedic Part
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
Milling Machine
Milling Machine
Use for precision milling of circuit board materials.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
Precision Drill
Precision Drill
Precision drill press for accuracy and controlled depth drilling.
CircuitMedic Part
Scraper
Hardened stainless steel tip for scraping solder mask and removing defects.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
3.4.2 Key and Slot Repair, Transplant Method
Damaged Key Slot
3.4.2 Key and Slot Repair, Transplant Method
Figure 1: Mill out the damaged area using a milling machine or Precision Drill System.
3.4.2 Key and Slot Repair, Transplant Method
Figure 2: Cut a groove into both sides of the key slot using a Micro-Drill System and carbide saw.
3.4.2 Key and Slot Repair, Transplant Method
Figure 3: Machine a tongue onto both sides of the replacement base material.
3.4.2 Key and Slot Repair, Transplant Method
Figure 4: Insert the replacement piece into the slot.
3.4.2 Key and Slot Repair, Transplant Method
Figure 5: Cut off excess material and file to match edge.
3.4.2 Key and Slot Repair, Transplant Method
Figure 6: Micro-Drill System.

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 carbide end mill. (See Figure 1)

  3. Clean the area.

  4. Install 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 in the edge to ensure that the new piece will fit properly. The groove width should be approx. 1/3 of the circuit board thickness. The groove depth should be approx. double the groove width. (See Figure 2)

  5. Cut a piece of replacement base board material that is the same thickness and type as the circuit board. The replacement piece should be longer than the length of 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 circuit board bordering the prepared area.

  7. Carefully check the fit of the replacement piece and then clean both the replacement piece and the slot. The replacement base material should fit firmly into the slot so that it will not move or fall out when epoxied in place.

  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 to the inside edges of the slot.

  11. Insert the replacement piece into the slot. Check alignment. Remove excess epoxy. (See Figure 4)

  12. If needed, apply additional epoxy to the edges of the slot. 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 temperature. 

  14. After the epoxy has cured remove the tape.

  15. If needed use a knife or scraper and scrape off any excess epoxy.

    Note
    If needed, apply additional thin coating to seal any scraped areas. 

  16. Cut off excess length of replacement material and file to match contour of existing edge. (See Figure 5)

  17. If a new slot is needed, machine using milling machine and appropriate milling cutter. Use great care to correctly relocate the slot.

  18. Clean the area.

Evaluation

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

Procedure for reference only.