Outline
This method is used on circuit boards to replace damaged or missing circuits on the circuit board surface.
Caution: The circuit widths, spacing, and current carrying capacity, must not be reduced below allowable tolerances.
Minimum Skill Level - Advanced
Recommended for technicians with soldering and component rework skills and exposure to most repair/rework procedures, but lacking extensive experience.
Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.
Micro Probes Sharp probes for dispensing adhesive and positioning small objects.
$5.00 Pkg/5
Scraper, Curved Tip Hardened stainless steel tip for scraping solder mask and removing defects.
$10.00 Each
Additional Items and Supplies
Cleaner General purpose cleaner for removing contamination.
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Continuity Meter Meter and probes to test for electrical continuity.
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Microscope Precision microscope with stand and lighting for work and inspection.
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Oven General purpose oven for drying, baking and curing epoxies.
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Solder Flux Used to prepare solder surfaces and to prevent formation of oxides during soldering.
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Soldering Iron Properly maintained soldering iron and properly sized soldering iron tips.
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Wipes Nonabrasive, low-linting wipes for cleanup.
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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
Circuit Tracks
Circuit Tracks are rectangular-shaped conductors made of 99.9% pure CDA 11000 copper. These rectangular ribbons closely conform to the original conductor dimensions. The replacement Circuit Track is bonded in place using epoxy.
115-5530 Circuit Track, .005" x .030" (.127 mm x .762 mm)
Color Agents
Color Agent is a one-part, air-drying, semi-paste ink commonly used to print hard surfaces, including circuit board base materials. Color Agent can be used to tint the color of epoxy used for solder mask repair or circuit baseboard repair. To use, mix a small amount of color agent with 2 part epoxy as the epoxy is initially mixed. Add more color agents to increase the color intensity if needed.
Figure 1: Scrape off any solder mask or coating from the ends of the remaining circuits.
Figure 2: Place the new Circuit Track in position and hold in place with high temperature tape.
Figure 3: Bend Circuit Track using 2 wood sticks.
Figure 4: Wide circuits that cannot be easily formed may be folded over to produce a sharp bend.
Figure 5: Form the final shape of the Circuit Track then hold in place with high temperature tape while soldering.
Figure 6: Coat the top and sides of the Circuit Track with epoxy.
Circuit Tracks
Circuit Tracks are rectangular-shaped conductors made of 99.9% pure CDA 11000 copper. These rectangular ribbons closely conform to the original conductor dimensions. The replacement Circuit Track is bonded in place using epoxy.
115-5530 Circuit Track, .005" x .030" (.127 mm x .762 mm)
Procedure
Clean the area.
Remove the damaged section of the circuit using a 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.
Note: It is essential that the board surface be smooth and flat. If the base material is damaged, see the appropriate procedure.
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 Circuit Track to match the width and thickness of the circuit to be replaced. (See Table Above) Cut a length approximately as needed. The Circuit Track should overlap the existing circuit a minimum of 2 times the circuit width.
Gently abrade the top and bottom surface of the Circuit Track with a buffer to remove the protective coating.
Note: A thin protective coating is applied to the Circuit Track to prevent oxidation.
Clean the Circuit Track.
If needed, the ends of the Circuit Track may be tinned with solder before lap soldering it in place.
If the Circuit Track is long or has bends, one end may be soldered before forming the new shape. Place the Circuit Track in position. The Circuit Track should overlap the existing circuit a minimum of 2 times the circuit width. The Circuit Track may be held in place with High-Temperature Tape. (See Figure 2)
Apply a small amount of liquid flux to the overlap joint.
Lap solder the Circuit Track to the circuit on the circuit board surface using solder and a soldering iron. Make sure the Circuit Track is properly aligned.
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.
Bend the Circuit Track as needed to match the shape of the missing circuit. (See Figure 3)
Note: Two wood sticks can be used to make sharp bends in the replacement Circuit Track. Use one stick to hold the Circuit Track at the bend location and use the other wood stick to form the shape as needed.
Wide circuits that cannot be easily formed may be folded over to produce a sharp bend. (See Figure 4)
Form the final shape of the jumper and hold it in place with tape. Lap solder the Circuit Track to the remaining circuit on the circuit board surface using solder and a soldering iron. Make sure the Circuit Track is properly aligned. Remove the tape used to hold the foil jumper. Clean the area. (See Figure 5)
Mix the Epoxy. If desired, add a color agent to the mixed epoxy to match the circuit board color.
Coat the top and sides of the Circuit Track with epoxy. The epoxy bonds the Circuit Track to the circuit board surface and insulates it. A wooden stick sharpened at one end may be used to apply and spread the epoxy. (See Figure 6)
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Caution: Some components may be sensitive to high temperature.
Apply surface coating to match prior coating as required.
Evaluation
Visual examination for alignment and overlap of foil jumper.
Visual examination of epoxy coating for texture and color match.
