Circuit Board Repair and Rework Guide > 3.0 Base Board Procedures > 3.5.3 Base Material Repair, Edge Transplant Method

3.5.3 Base Material Repair, Edge Transplant Method

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

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.

Damaged Base Material

Acceptability References
IPC-A-600	2.0	Externally Observable Characteristics
IPC-A-610	10.0	Laminate Conditions

Procedure Reference
CTC	2.1	Handling Electronic Assemblies
CTC	2.2.1	Cleaning, Local
CTC	2.2.2	Cleaning, Aqueous Batch Process
CTC	2.3.1	Coating Removal, Identification of Coatings
CTC	2.4.1	Coating Replacement, Solder Mask
CTC	2.4.2	Coating Replacement, Conformal Coatings/Encapsulants
IPC 7721	3.5.3	Base Material Repair, Edge Transplant Method
Tools and 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

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

1.	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.

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

3.	Clean the area.

4.	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).

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

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.	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.

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

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.	Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling

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

Figure 5: Micro-Drill System.

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.

15.	Clean the area.

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

17.	If needed, replace solder mask or conformal coating.

Evaluation

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