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.
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.
Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.
Wire Dots, Variety Pack
High-performance polymer film adhesive tape designed for tacking wires.
Wire Guide
Use to form bends in wires and hold wires during soldering and bonding.
Additional Items and Supplies
Cleaner
General purpose cleaner for removing contamination.
Microscope
Precision microscope with stand and lighting for work and inspection.
Oven
General purpose oven for drying, baking and curing epoxies.
Soldering Iron
Properly maintained soldering iron and properly sized soldering iron tips.
Wire
Solid conductor wire for conductor repair and jumpers.
Wire Stripper
Sharp wire strippers for stripping insulated wire.
Circuit Bond Epoxy
Circuit Bond is a clear, low viscosity, superior strength epoxy precisely measured out into two-compartment plastic packages, so it's easy to use, and there's no measuring. For over a decade, this high-strength epoxy has been qualified and used by thousands of high-rel electronics manufacturers across the globe.
1.
Circuit Bond has a working pot life of 30 minutes. It should not be mixed until ready to use.
2.
To use Circuit Bond, remove the plastic clip separating the resin and hardener. Squeeze back and forth from one half of the package to the other to mix the contents.
3.
Cut a corner off the package and squeeze all the contents into a Plastic Cup. Stir the contents to ensure it is thoroughly mixed.
4.
Circuit Bond may contain bubbles from the mixing process. If needed, use a vacuum system to remove bubbles.
5.
Color Agent can be mixed in with Circuit Bond to match surface colors if desired.
6.
Apply using a Foam Swab, Micro Probe, or Mixing Stick as required.
7.
Cure Circuit Bond for 24 hours at room temperature or 4 hours at 65°C (150°F).
Specifications
Packaging
2 gram pre-measured packages
Mix ratio
4 parts resin to 1 part hardener
Mix Ratio by Weight (R/H)
100/25
Color
Clear, transparent
Pot life
30 minutes
Cure cycle
24 hours at room temp (25 °C) or 4 hours @ 65°C
Thixotropic Index
1
Specific Gravity
1.20
Percent Solids
100%
Viscosity (after mixing)
2000 cps
Operating temperature range
-55°C to 135°C
Hardness
88 Shore D
Lap Shear, Alum to Alum
1100 psi
Glass Transition Temperature, Ultimate
92°C
Coefficient of Expansion, cm/cm/°C
6 E-05
Dielectric strength
400 volts/mil
Dielectric Constant, 1KHz@25°C
4
Shelf Life
6 months minimum
Wire Dots
Wire Dots are a wire tacking system consisting of pre-cut shapes of a thin, flexible polymer film coated on one side with a high-performance, electronics-grade permanent pressure-sensitive adhesive. The result is a highly conformable, high-strength bond, ideal for bonding jumper wires. Wire Dots perform well after exposure to high humidity, UV, immersion in water, and hot/cold cycles. Wire Dots will hold secure after exposure to numerous chemicals, including cleaning solutions/sprays, saponifiers, mild acids, and alkalies. And will hold secure through a typical circuit board hot water wash.
Short term (minutes/hours) 400°F (204°C) | Long term (days/weeks) 300°F (149°C)
Application
Specifically designed for long-term bonding to printed circuit boards and high surface energy plastics for the aerospace, medical and industrial equipment, automotive, appliance, and electronic
markets.
Figure 1: Scrape off any solder mask or coating from the ends of the remaining circuits
Figure 2: Lap solder the wire to one end of the circuit on the circuit board surface.
Figure 3: Form wire using a Wire Guide.
Figure 4: Form the final shape of the wire and solder in place.
Figure 5: Bond the wires to the surface with adhesive or Wire Dots.
Procedure
Clean the area.
Remove the damaged section of the 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.
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. A non-insulated wire may be used for short repairs if conductors are not crossed.
Clean the wire.
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.
Apply a small amount of liquid flux to the overlap joint.
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)
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.
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)
Remove any tape and clean the area.
Note: It may be necessary to encapsulate the solder joint connection if the electrical spacing is reduced or the connection is beneath a component.
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 temperatures.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
After the epoxy has cured, clean the area.
Evaluation
Visual examination for alignment and overlap of wire.
