4.2.4 Conductor Repair, Surface Wire Method

Outline

This method is used on circuit boards to replace damaged or missing circuits on the circuit board surface. A length of standard insulated or non-insulated wire is used to repair the damaged circuit.

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

Minimum Skill Level - Intermediate

Conformance Level - Medium

Tools and Materials

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

Cleaner General purpose cleaner for removing contamination.

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

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 Drill System Versatile power tool for milling, drilling, grinding, cutting and sanding.

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

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

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

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

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

Wire Solid conductor wire for conductor repair and jumpers.

Wire Dots Pre-cut polymer film tape with a high performance adhesive designed for tacking wires.

Wire Guide Use to form bends in wires and hold wires during soldering and bonding.

Wire Stripper Sharp wire strippers for stripping insulated wire.

Procedure

Procedure

1. Clean the area.
2. Remove the damaged section of the circuit using the knife. The damaged circuit should be trimmed back to a point where the circuit still has a good bond to the circuit 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
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 wire to match the width and thickness of the circuit to be replaced. Cut a length approximately as needed. See Table 1 for Solid Wire Equivalents.
   
   Table 1 - Solid Wire Equivalents
   

   Conductor Width 2 oz. Copper	Equivalent Solid Wire Diameter
   .010" (0.25 mm)	#34, .006" (0.15 mm)
   .015" (0.38 mm)	#32, .008" (0.20 mm)
   .020" (0.50 mm)	#31, .009" (0.23 mm)
   .031" (0.78 mm)	#29, .011" (0.28 mm)
   .082" (2.08 mm)	#26, .018" (0.46 mm)
   .125" (3.18 mm)	#23, .023" (0.58 mm)

   
   When using solid wire to repair a conductor, there should be no reduction in the cross-sectional area.
8. Strip the wire and tin the ends if needed. A non-insulated wire may be used for short repairs if conductors are not crossed.
9. Clean the wire.
10. If the wire is long or has bends, one end may be soldered prior to forming the new shape. Place the wire in position. The wire should overlap the existing circuit a minimum of 2 times the circuit width. The wire may be held in place with High-Temperature Tape tape during soldering.
    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.
11. Apply a small amount of liquid flux to the overlap joint.
12. Lap solder the wire to one end of the circuit on the circuit board surface. Make sure the wire is properly aligned. (See Figure 2)
13. Bend the wire as needed to match the shape of the missing circuit. (See Figure 3)
    Note: A Wire Guide Tool can be used to form the wire as needed.
14. Lap solder the other wire end to the remaining circuit on the circuit board surface using solder and a soldering iron. Make sure the wire is properly aligned. (See Figure 4)
15. Remove any tape and clean the area.
    Note: It may be necessary to encapsulate the solder joint connection if the electrical spacing is reduced or the connection is beneath a component.
16. If desired, bond the wire to the circuit board surface with adhesive, epoxy, or Wire Dots. (See Figure 5) Refer to Procedure 6.1.
    Caution: Some components may be sensitive to high temperatures.
17. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
18. After the epoxy has cured, clean the area.

Evaluation

1. Visual examination for alignment and overlap of wire.
2. Electrical tests as applicable.

Images

Conductor Repair, Surface Wire Method

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

Lap solder the wire to one end of the circuit on the circuit board surface.

Form wire using a Wire Guide.

Form the final shape of the wire and solder in place.

Bond the wires to the surface with adhesive or Wire Dots.