4.2.1 Conductor Repair, Foil Jumper, Epoxy Method

Outline

This method is used on circuit boards to replace damaged or missing circuits on the circuit board surface.

Caution: The circuit widths, spacing, and current carrying capacity, must not be reduced below allowable tolerances.

Minimum Skill Level - Advanced

Conformance Level - High

Tools and Materials

Abrader Mild abrasive for removing oxides and contaminants.

Circuit Bond Epoxy Clear, superior strength epoxy in two-compartment plastic packages.

Circuit Tracks Copper conductors to repair circuit board damage including traces and conductors.

Cleaner General purpose cleaner for removing contamination.

Cleaning Brushes Disposable brushes for solvent cleaning and application of coatings.

Color Agents One part, semi-paste ink used to tint the color of epoxy and for direct printing on circuit board surfaces.

Continuity Meter Meter and probes to test for electrical continuity.

Flex-Rack PCB Holder Sturdy rack for PCBs used for rework and positioning.

High Temp Tape Discs High temperature polyimide tape discs, .50" diameter.

Knife with #16 Blades A must-have tool for precise cutting, scraping and trimming.

Micro Probes Sharp probes for dispensing adhesive and positioning small objects.

Microscope Precision microscope with stand and lighting for work and inspection.

Mixing Picks Disposable mixing sticks for mixing and applying adhesives.

Oven General purpose oven for drying, baking and curing epoxies.

Precision Tool Set Nine precision-crafted tools for detailed circuit board work.

Repair Skills Practice Kit Training kit to practice circuit board repair skills prior to testing for certification.

Scraper, Curved Tip Hardened stainless steel tip for scraping solder mask and removing defects.

Solder Flux Used to prepare solder surfaces and to prevent formation of oxides during soldering.

Soldering Iron Properly maintained soldering iron and properly sized soldering iron tips.

Wipes Nonabrasive, low-linting wipes for cleanup.

Procedure

Procedure

1. Clean the area.
2. Remove the damaged section of the circuit using a knife. The damaged circuit should be trimmed back to a point where the circuit still has a good bond to the PC board surface.
   Note: Heat can be applied to the damaged circuit using a soldering iron to allow the circuit to be removed more easily.
3. Use a knife and scrape off any solder mask or coating from the ends of the remaining circuit. (See Figure 1)
4. Remove all loose material. Clean the area.
   Note: It is essential that the board surface be smooth and flat. If the base material is damaged, see the appropriate procedure.
5. Apply a small amount of liquid flux to the ends of the remaining circuit. Tin the exposed end of each circuit using solder and a soldering iron.
6. Clean the area.
7. Select a Circuit Track to match the width and thickness of the circuit to be replaced. (See Table Above) Cut a length approximately as needed. The Circuit Track should overlap the existing circuit a minimum of 2 times the circuit width.
8. Gently abrade the top and bottom surface of the Circuit Track with a buffer to remove the protective coating.
   Note: A thin protective coating is applied to the Circuit Track to prevent oxidation.
9. Clean the Circuit Track.
10. If needed, the ends of the Circuit Track may be tinned with solder before lap soldering it in place.
11. If the Circuit Track is long or has bends, one end may be soldered before forming the new shape. Place the Circuit Track in position. The Circuit Track should overlap the existing circuit a minimum of 2 times the circuit width. The Circuit Track may be held in place with High-Temperature Tape. (See Figure 2)
12. Apply a small amount of liquid flux to the overlap joint.
13. Lap solder the Circuit Track to the circuit on the circuit board surface using solder and a soldering iron. Make sure the Circuit Track is properly aligned.
    Note: If the configuration permits, the overlap solder joint connection should be a minimum of 3.00 mm (0.125") from the related termination. This gap will minimize the possibility of simultaneous reflow during soldering operations. Refer to 7.1 Soldering Basics.
14. Bend the Circuit Track as needed to match the shape of the missing circuit. (See Figure 3)
    Note: Two wood sticks can be used to make sharp bends in the replacement Circuit Track. Use one stick to hold the Circuit Track at the bend location and use the other wood stick to form the shape as needed.
15. Wide circuits that cannot be easily formed may be folded over to produce a sharp bend. (See Figure 4)
16. Form the final shape of the jumper and hold it in place with tape. Lap solder the Circuit Track to the remaining circuit on the circuit board surface using solder and a soldering iron. Make sure the Circuit Track is properly aligned. Remove the tape used to hold the foil jumper. Clean the area. (See Figure 5)
17. Mix the Epoxy. If desired, add a color agent to the mixed epoxy to match the circuit board color.
18. Coat the top and sides of the Circuit Track with epoxy. The epoxy bonds the Circuit Track to the circuit board surface and insulates it. A wooden stick sharpened at one end may be used to apply and spread the epoxy. (See Figure 6)
19. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
    Caution: Some components may be sensitive to high temperature.
20. Apply surface coating to match prior coating as required.

Evaluation

1. Visual examination for alignment and overlap of foil jumper.
2. Visual examination of epoxy coating for texture and color match.
3. Electrical tests as applicable.

Images

Conductor Repair, Foil Jumper, Epoxy Method

Scrape off any solder mask or coating from the ends of the remaining circuits.

Place the new Circuit Track in position and hold in place with high temperature tape.

Bend Circuit Track using 2 wood sticks.

Wide circuits that cannot be easily formed may be folded over to produce a sharp bend.

Form the final shape of the Circuit Track then hold in place with high temperature tape while soldering.

Coat the top and sides of the Circuit Track with epoxy.