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4.2.5 Conductor Repair, Through Board Wire
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 wire will be subsequently subjected to a mass soldering operation.
Minimum Skill Level - Advanced
Recommended for technicians with soldering and component rework skills and exposure to most repair/rework procedures, but lacking extensive experience.
Conformance Level - Medium
This procedure may have some variance with the physical character of the original and most likely varies with some of the functional, environmental and serviceability factors.
Acceptability References
IPC-A-610 11.0 Discrete Wiring
Procedure References
1.0 Foreword
2.1 Handling Electronic Assemblies
2.2 Cleaning
2.5 Baking And Preheating
2.7 Epoxy Mixing and Handling
IPC7721 4.2.5 Conductor Repair, Through Board Wire Method
Tools and Materials
Cleaner
Cleaner
General purpose cleaner for removing contamination.
CircuitMedic Part
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
Microscope
Microscope
It is a challenge to undertake precision repair without a good microscope.
CircuitMedic Part
Micro Drill System
Versatile power tool for milling, drilling, grinding, cutting and sanding circuit boards.
Soldering Iron
Soldering Iron, Solder and Flux
A well maintained soldering iron is a must at every tech bench.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Wire
Wire
Solid conductor wire for conductor repair and jumpers.
CircuitMedic Part
Wire Dots
Polymer film coated on one side with a high performance adhesive for tacking wires.
CircuitMedic Part
Wire Guide
Use to form bends in wires and hold wires during soldering and bonding.
Images and Figures
4.2.5  Conductor Repair, Through Board Wire Method
Damaged Conductor
4.2.5  Conductor Repair, Through Board Wire Method
Figure 1: Scrape off any solder mask or coating from the ends of the remaining circuits
4.2.5  Conductor Repair, Through Board Wire Method
Figure 2: Drill through the board adjacent to both ends of the remaining circuits.
4.2.5  Conductor Repair, Through Board Wire Method
Figure 3: Bend the stripped wire over the prepared circuits in line with the circuits.
4.2.5  Conductor Repair, Through Board Wire Method
Figure 4: Lap solder the wire to the circuits on the circuit board surface.
***image6***
Procedure 
  1. Clean the area.

  2. Remove the damaged section of 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. 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 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 temperature.  

  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.

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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