4.2.2 Conductor Repair, Foil Jumper, Film Adhesive Method
Outline
This method is used to replace damaged or missing circuits on the circuit board surface.
Caution: It is essential that the board surface be extremely smooth and flat. If the baseboard is damaged see appropriate procedure.
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.
Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.
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.
Tweezers
Multiple sizes and tip configurations of tweezers for various small parts handling needs.
Bonding Iron Tips
Bonding Iron Tips fit into the handheld Bonding Iron. The bottom surface of each Bonding Tip is used to apply heat and pressure to bond adhesive-backed replacement lands, pads, and edge contacts to a circuit board surface. The pressure/force listed is the recommended load in pounds to apply to the top surface of the replacement adhesive-backed pads, lands, and conductors. The load is based on the Bonding Tip surface area to meet the recommended load for Circuit Frames at 200 - 400 psi.
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 Frames
Circuit Frames have a dry-film adhesive backing that is heat-cured in 30 seconds. Use Circuit Frames to repair and replace damaged surface mount pads, lands and conductors without the mess of liquid epoxy, with a bond strength equal to the original, in just a few minutes. The dry-film adhesive backing makes this delicate repair procedure easy, fast, and highly reliable. Circuit Frames are available with a bright tin, tin/lead and nickel/gold plating finishes. This reliable IPC recommended procedure meets the highest conformance level for this type of repair. For over 30 years Circuit Frames have been used by thousands of commercial, medical and military manufacturers around the globe. Below are examples for some Circuit Frame patterns.
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: Remove solder mask from the connecting circuit.
Figure 2: Sample frame or replacement conductors with dry film adhesive backing.
Figure 3: Scrape off epoxy bonding film from solder joint connection area on back of new conductor.
Figure 4: Cut out the new circuit. Cut from the plated side
Figure 5: Place the new conductor in place using high temperature tape.
Figure 6: Bonding Iron used to thermally bond dry film adhesive backed replacement conductors.
Figure 7: Completed repair.
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 PC board surface.
Use the knife and scrape off any epoxy residue, contamination, or burned material from the board surface.
Scrape off any solder mask or coating from the connecting circuit. (See Figure 1)
Clean the area.
Apply a small amount of liquid flux to the connection area on the board surface and tin with solder. Clean the area. The length of the overlap solder connection should be a minimum of 2 times the circuit width.
Select a replacement circuit with film adhesive backing that most closely matches the size of the conductor to be replaced. If a special size or shape is needed, it can be custom fabricated. (See Figure 2)
Note: New conductors are fabricated from copper foil. The foil is plated on the top side with solder, and an epoxy bonding film is applied to the bottom side.
Before trimming out the new conductor, carefully scrape off the adhesive epoxy film from the solder joint connection area on the back of the new conductor. (See Figure 3)
Caution: Scrape off the epoxy backing only from the joint connection area. When handling the new conductor, avoid touching the epoxy backing with your fingers or other materials that may contaminate the surface and reduce the bond strength.
Cut out and trim the new conductor. Cut out from the plated side. Cut the length to provide the maximum allowable circuit overlap for soldering. Minimum 2 times the circuit width. (See Figure 4)
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.
Place a piece of High-Temperature Tape tape over the top surface of the new conductor. Place the new conductor into position on the circuit board surface using tape to help in alignment. Leave the tape in place during the bonding cycle. (See Figure 5)
Select a bonding tip with a shape to match the shape of the new conductor.
Note: The bonding tip should be as small as possible but should completely cover the entire width of the new conductor.
Position the circuit board so that it is flat and stable. Gently place the hot bonding tip onto the High-Temperature Tape covering the new circuit. Apply pressure as recommended in the manual of the repair system or repair kit for 5 seconds to tack the circuit in place. Carefully peel off the tape. (See Figure 6)
Gently place the bonding tip directly onto the new circuit. Apply pressure as recommended in the manual of the repair system or repair kit for an additional 30 seconds to fully bond the new circuit. The new circuit is fully cured. Carefully clean the area and inspect the new circuit for proper alignment.
Apply a small amount of liquid flux to the lap solder joint connection area and solder the circuit foil jumper from the new conductor to the circuit on the circuit board surface. Use minimal flux and solder to ensure a reliable connection. High-Temperature Tape may be placed over the top of the new conductor to prevent excess solder overflow.
Mix epoxy and coat the lap solder joint connections. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Caution: Some components may be sensitive to high temperatures.
Apply surface coating to match prior coating as required.
