Circuit Technology Center

3.4.1 Key and Slot Repair, Epoxy Method

This method is used to repair 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 damage to the conductive patterns, contacts and components.

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.

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 3.4.1 Key and Slot Repair, Epoxy Method
Tools and Materials
Ball Mills, Abrasives, Cutting Tools
Ball mills, abrasives and cutting tools for working on circuit boards.
General purpose cleaner for removing contamination.
Cleaning Brushes
Disposable brushes for use with solvents for cleaning and application of coatings.
Color Agents
Use to tint the color of epoxy used for solder mask repair or circuit base board repair.
Circuit Bond Epoxy
Clear, superior strength epoxy in two-compartment plastic packages.
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 circuit boards.
Micro Probes
Use to dispense a minute amount of adhesive and for micro-positioning of small objects.
General purpose oven for drying, baking and curing epoxies.
Hardened stainless steel tip for scraping solder mask and removing defects.
Nonabrasive, low-linting wipes for cleanup.
Images and Figures
3.4.1 Key and Slot Repair, Epoxy Method
Damaged Key Slot
3.4.1 Key and Slot Repair, Epoxy Method
Figure 1: Mill away the damaged board base material using a Micro-Drill System and ball mill.
3.4.1 Key and Slot Repair, Epoxy Method
Figure 2: Apply epoxy to the edges of the key slot using a mixing stick or micro-probe.

3.4.1 Key and Slot Repair, Epoxy Method
Figure 3: Completed key slot repair.
3.4.1 Key and Slot Repair, Epoxy Method
Figure 4: Micro-Drill System.
  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 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.
    Caution: Abrasion operations can generate electrostatic charges.
  3. Remove all loose material and clean the area.
  4. Apply high-temperature tape to the surface of the circuit board adjacent to the slot. The tape should protect any adjacent contacts or components.
    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.
  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 micro-probe may be used. (See Figure 2)
    Note: A slight overfill of epoxy may be desired to allow for shrinkage when 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. If needed, use a knife or scraper and scrape off any excess epoxy.
  10. If precision is required, machine the edges of the slot using a milling machine or precision drill system and appropriate milling cutter. Use great care to correctly relocate the slot.
    Note: If needed, apply an additional thin coating to seal any scraped areas.
  11. Clean the area.
  1. Visual examination and measurement of key slot location and dimension.
Procedure for reference only.