4.2.4 Conductor Repair, Surface Wire Method

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Printed Board Type: N/A
Skill Level: Intermediate
Conformance Level: Medium
Revision: D
Revision Date: Jul 7, 2000

Damaged Conductor

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.  

ACCEPTABILITY REFERENCES
IPC-A-610 11.0	Discrete Wiring
PROCEDURE REFERENCE
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 & MATERIALS
Cleaner
Epoxy
Flux, Liquid
Knife
Microscope
Oven
Scraper
Solder
Soldering Iron with Tips
Tape Dots
Tape, Kapton
Wipes
Wire
Wire Guide

PROCEDURE

1. Figure 1: Scrape off any solder mask or coating from the ends of the remaining circuits

   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. Figure 2: Lap solder the wire to one end of the circuit on the circuit board surface.

   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. Figure 3: Form wire using a Wire Guide.

   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 Kapton 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. Refer to 7.1 Soldering Basics.  

11. Apply a small amount of liquid flux to the overlap joint.
    
    

12. Figure 4: Form the final shape of the wire and solder in place

    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 Kapton 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. Figure 5: Bond the wires to the surface with adhesive or Tape Dots.

    If desired bond the wire to the circuit board surface with adhesive, epoxy or Tape 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.