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4.2.4 Conductor Repair, Surface Wire Method
Outline
This method is used on circuit boards to replace damaged or missing circuits on the PC 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
Recommended for technicians with skills in basic soldering and component rework, but may be inexperienced in general repair/rework procedures.

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
6.1 Jumper Wires
IPC7721 4.2.4 Conductor Repair, Surface Wire Method
Tools and Materials
CircuitMedic Part
Alcohol Swab
Self-saturating Isopropyl alcohol swab. Squeeze handle to release alcohol.
Cleaner
Cleaner
General purpose cleaner for removing contamination.
CircuitMedic Part
Cleaning Brushes
Disposable brushes for use with solvents for cleaning and application of coatings.
CircuitMedic Part
Circuit Bond Packs
Clear, superior strength epoxy in two-compartment plastic packages
CircuitMedic Part
High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.
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.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
CircuitMedic Part
Scraper
Hardened stainless steel tip for scraping solder mask and removing defects.
Soldering Iron
Soldering Iron, Solder and Flux
A well maintained soldering iron is a must at every tech bench.
Wire
Wire
Solid conductor wire for conductor repair and jumpers.
CircuitMedic Part
Wire Dots
Pre-cut polymer film tape with a high performance adhesive designed for tacking wires.
CircuitMedic Part
Wire Guide
Use to form bends in wires and hold wires during soldering and bonding.
Wire Stripper
Wire Stripper
Sharp wire strippers for stripping insulated wire.
Images and Figures
4.2.4 Conductor Repair, Surface Wire Method
Damaged Conductor
4.2.4 Conductor Repair, Surface Wire Method
Figure 1: Scrape off any solder mask or coating from the ends of the remaining circuits
4.2.4 Conductor Repair, Surface Wire Method
Figure 2: Lap solder the wire to one end of the circuit on the circuit board surface.
4.2.4 Conductor Repair, Surface Wire Method
Figure 3: Form wire using a Wire Guide.
4.2.4 Conductor Repair, Surface Wire Method
Figure 4: Form the final shape of the wire and solder in place
4.2.4 Conductor Repair, Surface Wire Method
Figure 5: Bond the wires to the surface with adhesive or Tape Dots.

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 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. 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 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 temperature.  

  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.

Procedure for reference only.