4.2.5 Conductor Repair, Through Board Wire Method

Printed Board Type: R
Skill Level: Advanced
Conformance Level: Medium
Revision: D
Revision Date: Jul 7, 2000

OUTLINE

Damaged Conductor

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.   

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 4.2.5	Conductor Repair, Through Board Wire Method

TOOLS & MATERIALS
Cleaner
Flux, Liquid
Knife
Micro-Drill System
Microscope
Solder
Soldering Iron with Tips
Tape Dots
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: Drill through the board adjacent to both ends of the remaining circuits.

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

   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. Figure 4: Lap solder the wire to the circuits on the circuit board surface.

    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.