Outline
This method replaces a damaged edge contact with a new edge contact. The new edge contact is bonded to the circuit board surface using liquid epoxy.
Caution: It is essential that the board surface be smooth and flat. If the base material is damaged, see the appropriate procedure.
Note: This method uses replacement edge contacts that are fabricated from copper foil. They are available in hundreds of sizes and shapes and are generally supplied in either plain copper, solder plated, or nickel and gold plated. If a special size or shape is needed, it can be custom fabricated.
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 - 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.
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.
Wipes
Nonabrasive, low-linting wipes for cleanup.
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.
Images and Figures
Damaged Edge Contact
Figure 1: Remove the defective edge contact and remove solder mask from the connecting circuit.
Figure 2: Select a replacement contact that matches the missing contact.
Figure 3: Cut out the new edge contact.
Figure 4: Place the new edge contact in place using Kapton tape.
Figure 5: File overhanging piece of new edge contact to blend with existing bevel.
Figure 6: Completed repair .
Procedure
Clean the area.
Remove the defective edge contact and a short length of the connecting circuit. The heat from a soldering iron will allow the old contact to be removed more easily. (See Figure 1)
Use the knife and scrape off any epoxy residue, contamination, or burned material from the board surface.
Caution: Abrasion operations can generate electrostatic charges.
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.
The area for the new edge contact on the board surface must be smooth and flat. If internal fibers of the board are exposed or deep scratches exist on the surface, they should be repaired. Refer to appropriate procedure.
Select a new edge contact that most closely matches the edge contact to be replaced. (See Figure 2)
Cut out and trim the new edge contact. Cut out from the plated side. Cut the length to provide the maximum allowable joint if lap soldering. Minimum 2 times the circuit width. Leave the new edge contact extra long. The excess material will be trimmed after curing. (See Figure 3)
Note: The new replacement edge contact may be trimmed from a copper sheet.
Mix the epoxy and apply a small amount to the surface where the new contact will be placed.
Place a piece of High-Temperature Tape over the top surface of the new edge contact. Position the new edge contact on the circuit board surface using the tape to aid in alignment. (See Figure 4)
Note: Allow the edge contact to overhang the edge of the circuit board. Leave the tape in place during the bonding cycle.
Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Caution: Some components may be sensitive to high temperatures.
After the epoxy has cured, remove the High-Temperature Tape used for alignment. Carefully clean and inspect the new pad for proper alignment.
Note: Additional epoxy can be applied around the perimeter of the new edge contact to provide additional bond strength.
If the new edge contact has a connecting circuit apply a small amount of liquid flux to the lap solder joint connection area and solder the circuit from the new edge contact 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 edge contact to prevent excess solder overflow.
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.
Remove the tape and clean the area.
Trim the extending edge of the new edge contact with a file. File parallel to the beveled edge until the excess material has been removed. (See Figure 5)
If sealing the lap solder joint connection is required, mix epoxy and coat the lap solder joint connections. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
If plating is required refer to appropriate procedure.
Apply surface coating to match prior coating as required.
Evaluation
Visual examination, measurement of new pad width, and spacing.
