OUTLINE
This procedure is used to repair mechanical or thermal damage to circuit board base material. This method is used when extended areas of base material must be completely replaced. This method may be used on single sided, double sided or multilayer circuit boards or assemblies.

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 7722	2.2	Cleaning
CTC 7721	2.5	Baking and Preheating
CTC 7721	3.5.2	Base Material Repair, Area Transplant Method

TOOLS & MATERIALS

Ball Mills
Base Board Repair Kit
Base Board Material
Cleaner
Color Agents
End Mills
Epoxy
Knife
Micro-Drill System
Microscope
Oven
Precision Drill System
Scraper
Surgical Saw
Tape, Kapton
Wipes

PROCEDURE

1. Clean the area



2. Mill away the damaged board material using the Micro-Drill System and ball mill. Remove all evidence of the damaged material. No fibers of laminate material should be exposed. At the surface file the edges to ensure that the opening is rectangular or uniform in shape. (See Figure 1).




CAUTION
Abrasion operations can generate electrostatic charges.

 

3. Clean the area.



4. Bevel the edge using the Micro-Drill System and ball mill or using a file. (See Figure 2).


Or

Install an end mill into the chuck of a Precision Drill System. Set the speed to maximum and machine a step or lap joint in the edge of the circuit board where the new base material will be installed. The depth and width of the step should be approximately 1/2 of the circuit board thickness. (See Figure 3).



CAUTION
Exercise care to avoid damage to any internal conductors. If any internal conductors are damaged, surface wires may be required.

 

5. Cut or machine a piece of replacement base board material that is the same thickness and type as the piece removed. The replacement piece must be precisely the same size and shape of the opening including the step joint.



6. Install an end mill into the chuck of a Precision Drill Press. Machine a step onto the entire mating edge of the replacement base material. The dimensions of the step should match the size of the step in the circuit board milled groove. (See Figure 4).



7. Where required apply Kapton tape to protect exposed parts of circuit board bordering the prepared area.



8. Check the fit to be sure the new base material properly mates with the step in the circuit board.



9. Mix the epoxy.



10. Coat both the tongue and groove surfaces with epoxy and fit together. (See Figure 5). Remove excess epoxy.



11. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.



12. After the epoxy has cured remove the High Temperature Tape.



13. If needed scrape off any excess epoxy using a knife or scraper.




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

 

14. Clean the area.



15. Complete by drilling holes, slots, etc. or adding circuitry as required.



16. If solder mask replacement or conformal coating is needed see appropriate procedure.

EVALUATION

1. Dimensions of area replaced should be checked to conform to specifications required.