OUTLINE
This procedure is used to repair minor damage to circuit base board material. Scrapes and scratches in the base board material may be caused by accidents during handling. Burns in the base material may be caused by improper use of soldering and desoldering tools.

CAUTION
This method may be used when the damage extends deep into the base material, but not completely through. If the base board material is damaged completely through, see Procedure No. 3.5.2 or 3.5.3.

CAUTION
Surface circuits may need to be replaced in the damaged area. Be sure that the appropriate circuit diagrams, or photographs reflecting the original circuits are available so that they may be replaced after repairing the base board material. Damage to internal circuits or planes may have to be restored using surface wires.
  

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	3.5.1	Base Material Repair, Epoxy Method

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

PROCEDURE

1. Clean the damaged area.



2. Scrape away the damaged base board material using a knife. All damaged base board material and solder mask must be removed at the surface. (See Figure 1).


or

Mill away the damaged base board material using the Micro-Drill System and ball mill. All damaged base board material and solder mask must be removed. (See Figure 2).



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.



NOTE
An undercut to enhance mechanical strength may be desired for class 3 product. (See figure #3).

 

3. Remove all loose material and clean the area.



4. Where needed, apply Kapton tape to protect exposed parts of circuit board.




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. Fill the area with epoxy up to and flush with the circuit board surface. No fibers of laminate material should be exposed. A mixing stick sharpened at the end may be used to apply and spread the epoxy. For large areas, apply the epoxy with a foam swab to create a texture in the surface. (See Figures 4 and 5).




NOTE
A slight overfill of epoxy may be desired to allow for shrinkage when epoxy cures.

NOTE
Epoxy may be applied using a foam swab to restore the surface appearance.

 

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. Scrape until the new epoxy surface is level with the surrounding PC board surface.



10. Remove all loose material. Clean the area




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

 

EVALUATION

1. Visual examination for texture and color match.



2. Electrical tests to conductors around the repaired area as applicable.