4.2.5 Conductor Repair, Through Board 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.

Caution: This method is not allowed when the wire will be subsequently subjected to a mass soldering operation.

Minimum Skill Level - Advanced

Conformance Level - Medium

Tools and Materials

Ball Mills, Abrasives, Cutting Tools Ball mills, abrasives and cutting tools for working on circuit boards.

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.

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.

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

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

Wipes Nonabrasive, low-linting wipes for cleanup.

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 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.
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. Drill through the board adjacent to both ends of the remaining circuits. Drill the hole slightly larger than the wire diameter to be used. (See Figure 2)
    Caution: Review circuit diagrams to be sure no surface or internal circuits will be damaged or shorted.
11. Position the wire on the opposite side from the repair and insert the stripped ends into the drilled holes.
12. Bend the stripped wire over the prepared circuits in line with the circuits. The wire should overlap the existing circuit a minimum of 2 times the circuit width. (See Figure 3)
    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.
13. Apply a small amount of liquid flux to the overlap joint.
14. Lap solder the wire to the circuits on the circuit board surface. Make sure the wire is properly aligned. (See Figure 4)
15. Form the wire on the opposite side to match the shape of the missing circuit, if desired.
16. Clean the area.
    Note: It may be necessary to encapsulate the solder joint connection if the electrical spacing is reduced.
17. If desired, bond the wire to the circuit board surface with adhesive, epoxy or Tape Dots. Refer to Section 6.0.
    Caution: Some components may be sensitive to high temperatures.
18. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling
19. 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, Through Board Wire Method

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

Drill through the board adjacent to both ends of the remaining circuits.

Bend the stripped wire over the prepared circuits in line with the circuits.

Lap solder the wire to the circuits on the circuit board surface.