Circuit Board Rework and Repair Guide

3.5.3 Base Material Repair, Edge Transplant Method

Printed Board Type: R/W
Skill Level: Expert
Conformance Level: High
Revision: D
Revision Date: Jul 7, 2000

OUTLINE

Damaged Base Material

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
2.1	Handling Electronic Assemblies
2.2	Cleaning
2.3.1	Coating Removal, Identification Of Coatings
2.4.1	Coating Replacement, Solder Mask
2.4.2	Coating Replacement, Conformal Coatings/Encapsulants
IPC7721 3.5.3	Base Material Repair, Edge Transplant Method

Figure 1: Cut away damaged base material with the Saw or milling cutter.

TOOLS & MATERIALS
Ball Mills
Base Board Repair Kit
Base Board Material
Brushes
Cleaner
Color Agent
End Mills
Epoxy
Foam Swabs
Knife
Micro Drill System
Microscope
Milling Machine
Oven
Precision Drill System
Saw
Scraper
Tape, Kapton
Wipes

PROCEDURE

1. Figure 2: Cut a groove into the edge of the circuit board.

   Clean the area

    

2. Cut away the damaged board material using the Saw or milling cutter. Remove all evidence of the damaged material. No fibers of laminate material should be exposed. File the edge to ensure that the edge is flat. (See Figure 1).

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

    

3. Clean the area.

    

4. Figure 3: Mill a tongue onto the edge of the replacement base material

   Install a carbide saw into the Micro-Drill System. Set the speed to maximum and machine a groove in the edge of the circuit board where the new base material will be installed. The groove must be centered in the edge to ensure that the new piece will fit properly. The groove width should be approximately 1/3 of the PC board thickness. The groove depth should be approximately double the groove width. (See Figure 2).

    

5. Cut a piece of replacement base board material that is the same thickness and type as the piece removed. The replacement piece may be oversized, the excess material will be removed after the replacement piece has been epoxied in place.

    

6. Figure 4: Check fit of new base material. The tongue must mate with the groove in circuit board.

   Install an end mill into the chuck of a milling machine. Machine a tongue onto the entire mating edge of the replacement base material. The dimensions of the tongue should match the size of the milled groove. (See Figure 3).

    

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 groove in the circuit board. (See Figure 4). 
   
   
9. Mix the epoxy.

    

10. Coat both the tongue and groove surfaces with epoxy and fit together. Remove excess epoxy.

     

11. Figure 5: Excess material trimmed to size.

    Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling

     

12. After the epoxy has cured remove the Kapton tape.

     

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

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

     

14. Saw or mill off excess base material and file flush with existing edge. (See Figure 5).

     

15. Clean the area.

     

16. Figure 6: Completed repair.

    Complete by drilling holes, slots, etc. or adding circuitry as required. (See Figure 6).

     

17. If needed, replace solder mask or conformal coating. (See Figure 6).

EVALUATION

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