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3.4.1 Key and Slot Repair, Epoxy Method More Guides
Outline
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
CircuitMedic Part
Alcohol Swab
Self-saturating Isopropyl alcohol swab. Squeeze handle to release alcohol.
CircuitMedic Part
Ball Mills, Abrasives, Cutting Tools
Ball mills, abrasives and cutting tools for working on circuit boards.
CircuitMedic Part
Cleaning Brushes
Disposable brushes for use with solvents for cleaning and application of coatings.
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.
CircuitMedic Part
Micro Probes
Use to dispense a minute amount of adhesive and for micro-positioning of small objects.
CircuitMedic Part
Scraper
Hardened stainless steel tip for scraping solder mask and removing defects.
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.
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 keyslot. (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 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 temperature.

  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 additional thin coating to seal any scraped areas. 

  11. Clean the area.

Evaluation

  1. Visual examination and measurement of key slot location and dimension.
Procedure for reference only.
Customer Comments
"We had never considered sending our rework projects until recently. The cost savings since we started using Circuit Technology Center has been significant. I hope we never have such a massive rework project again, but if we, do you'll be the first to get a call"
N.C. Fort Wayne, IN USA
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