First-Aid Kits for Circuit Boards
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3.5.3 Base Material Repair, Edge Transplant Method
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.
Minimum Skill Level - Expert
Recommended for technicians with advanced soldering and component rework skills and extensive experience in most repair/rework procedures.
Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.
| Acceptability References |
| IPC-A-600 2.0 |
Externally Observable Characteristics |
| IPC-A-610 10.0 |
Laminate Conditions |
| Tools and Materials |
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Cleaner
General purpose cleaner for removing contamination. |
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Color Agents
Use for matching epoxy to existing solder mask and coating colors. |
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End Mills
Designed for end cutting and hole boring. |
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Epoxy Kit
High temperature epoxy for masking and structural repairs to circuit boards. |
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Microscope
It is a challenge to undertake precision repair without a good microscope. |
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Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards. |
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Milling Machine
Use for precision milling of circuit board materials. |
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Oven
General purpose oven for drying, baking and curing epoxies. |
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Precision Drill
Precision drill press for accuracy and controlled depth drilling. |
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Syringes
Polypropylene syringe barrels with stainless steel dispensing tips. |
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Wipes
Nonabrasive, low-linting wipes for cleanup. |
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| Images and Figures |
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| Damaged Base Material |
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| Figure 1: Cut away damaged base material with the Saw or milling cutter. |
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| Figure 2: Cut a groove into the edge of the circuit board. |
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| Figure 3: Mill a tongue onto the edge of the replacement base material |
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| Figure 4: Check fit of new base material. The tongue must mate with the groove in circuit board. |
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| Figure 5: Excess material trimmed to size. |
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| Figure 6: Completed repair. |
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Procedure
- Clean the area.
- 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.
- Clean the area.
- 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).
- Cut a piece of replacement base board material that is the same thickness and type as the piece removed. The replacement piece may be over-sized, the excess material will be removed after the replacement piece has been epoxied in place.
- 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).
- Where required apply Kapton tape to protect exposed parts of circuit board bordering the prepared area.
- Check the fit to be sure the new base material properly mates with the groove in the circuit board. (See Figure 4).
- Mix the epoxy.
- Coat both the tongue and groove surfaces with epoxy and fit together. Remove excess epoxy.
- Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
- After the epoxy has cured remove the Kapton tape.
- If needed, scrape off any excess epoxy using the knife or scraper.
Note
If needed, apply additional thin coating to seal any scrapped areas.
- Saw or mill off excess base material and file flush with existing edge. (See Figure 5).
- Clean the area.
- Complete by drilling holes, slots, etc. or adding circuitry as required. (See Figure 6).
- If needed, replace solder mask or conformal coating. (See Figure 6).
Evaluation
- Dimensions of area replaced should be checked to conform to specifications required.
This procedure is for reference only. Refer to the Procedure References listed above, or contact Circuit Technology Center for appropriate industry approved references.
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CircuitMedic
22 Parkridge Road, Haverhill, MA 01835 USA
Phone: 978-373-1600 - Fax: 978-372-5700
Division of Circuit Technology Center, Inc.
Copyright © 2012 All rights reserved.
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ISO9000:2008 Certified
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Member Since 1986
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