4.6.1 Edge Contact Repair, Epoxy Method

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

Conformance Level - Medium

Tools and Materials

Abrader Mild abrasive for removing oxides and contaminants.

Abrasive Pads Light duty abrasive scrubbing pads to remove contamination and blend surfaces.

Ball Mills, Abrasives, Cutting Tools Ball mills, abrasives and cutting tools for working on circuit boards.

Circuit Bond Epoxy Clear, superior strength epoxy in two-compartment plastic packages.

Circuit Bonding System System to repair damaged conductors, BGA pads, and SMT pads.

Circuit Frames Circuit Frames for surface mount pad, BGA pad and conductor repair.

Cleaner General purpose cleaner for removing contamination.

Flex-Rack PCB Holder Sturdy rack for PCBs used for rework and positioning.

High Temp Tape Discs High temperature polyimide tape discs, .50" diameter.

Knife with #16 Blades A must-have tool for precise cutting, scraping and trimming.

Microscope Precision microscope with stand and lighting for work and inspection.

Oven General purpose oven for drying, baking and curing epoxies.

Precision Tool Set Nine precision-crafted tools for detailed circuit board work.

Repair Skills Practice Kit Training kit to practice circuit board repair skills prior to testing for certification.

Scraper, Curved Tip Hardened stainless steel tip for scraping solder mask and removing defects.

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.

Procedure

Procedure

1. Clean the area.
2. 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)
3. Use the knife and scrape off any epoxy residue, contamination, or burned material from the board surface.
   Caution: Abrasion operations can generate electrostatic charges.
4. Scrape off any solder mask or coating from the connecting circuit. (See Figure 1)
5. Clean the area.
6. 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.
7. 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.
8. Select a new edge contact that most closely matches the edge contact to be replaced. (See Figure 2)
9. 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.
10. Mix the epoxy and apply a small amount to the surface where the new contact will be placed.
11. 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.
12. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
    Caution: Some components may be sensitive to high temperatures.
13. 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.
14. 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.
15. Remove the tape and clean the area.
16. 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)
17. 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.
18. If plating is required refer to appropriate procedure.
19. Apply surface coating to match prior coating as required.

Evaluation

1. Visual examination, measurement of new pad width, and spacing.
2. Electrical continuity measurement.

Images

Edge Contact Repair, Epoxy Method

Remove the defective edge contact and remove solder mask from the connecting circuit.

Select a replacement contact that matches the missing contact.

Cut out the new edge contact.

Place the new edge contact in place using Kapton tape.

File overhanging piece of new edge contact to blend with existing bevel.

Completed repair .