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.

   

ACCEPTABILITY REFERENCES
IPC-A-600	2.0	Externally Observable Characteristics
IPC-A-610	10.0	Laminate Conditions
PROCEDURE REFERENCE
CTC 7721	1.0	Foreword
CTC 7721	2.1	Handling Electronic Assemblies
CTC 7721	2.2	Cleaning
CTC 7721	2.5	Baking and Preheating
CTC 7721	2.7	Epoxy Mixing and Handling
IPC 7721	3.4.1	Key and Slot Repair, Epoxy Method

TOOLS & MATERIALS
Ball Mills
Base Board Repair Kit
Cleaner
Color Agents
Epoxy
Knife
Micro-Drill System
Mixing Sticks
Oven
Scraper
Tape, Kapton
Wipes

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 Kapton tape to the surface of the circuit board adjacent to the slot. The Kapton tape should protect any adjacent contacts or components.




NOTE
The circuit board may be preheated prior to filling the area with epoxy. A preheated PC 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 PC board color.



6. Apply a small amount of epoxy to the edges of the slot. A mixing stick sharpened at the end 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 Kapton 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