Circuit Board Repair and Rework Guide > 4.0 Conductor Procedures > 4.2.5 Conductor Repair, Through Board Wire Method

4.2.5 Conductor Repair, Through Board Wire Method

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

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.

Damaged Conductor

Acceptability References
IPC-A-610	11.0	Discrete Wiring
Procedure References
CTC	1.0	Foreword
CTC	2.1	Handling Electronic Assemblies
CTC	2.2.1	Cleaning, Local
CTC	2.2.2	Cleaning, Aqueous Batch Process
CTC	2.5	Baking and Preheating
CTC	2.7	Epoxy Mixing and Handling
CTC	6.1	Jumper Wires
IPC7721	4.2.5	Conductor Repair, Through Board Wire Method
Tools and Materials
Cleaner Flux, Liquid Knife Micro-Drill System Microscope Solder		Soldering Iron with Tips Wire Dots Wipes Wire Wire Guide

Procedure

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

Clean the area.

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.

Use a knife and scrape off any solder mask or coating from the ends of the remaining circuit. (See Figure 1).

Remove all loose material. Clean the area.

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.

Clean the area.

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.

Strip the wire and tin the ends if needed. Non insulated wire may be used for short repairs if conductors are not crossed.

Clean the wire.

Figure 2: Drill through the board adjacent to both ends of the
remaining circuits.

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.

Figure 3: Bend the stripped wire
over the prepared circuits in line
with the circuits.

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.

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

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 Wire 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.