4.6.2 Edge Contact Repair, Film Adhesive Method

Outline

This method replaces a damaged edge contact with a new edge contact. The new edge contact has a dry-film adhesive backing and is bonded to the circuit board surface using a Bonding Iron.

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 and have a dry film adhesive coating on the back. They are available in hundreds of sizes and shapes and are generally supplied nickel and gold plated. If a special size or shape is needed, it can be custom fabricated.

Minimum Skill Level - Advanced

Conformance Level - High

Tools and Materials

Bonding Iron Delivers the optimal heat for curing adhesive bonding film.

Bonding Tips Bonding Tips used to bond adehesive backed Circuit Frames.

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.

Gold Contact Plating Kit Kit to repair damaged gold contacts and pads on circuit boards.

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.

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)
   Note: The new replacement edge contact may be trimmed from a copper sheet.
9. Before trimming out the new edge contact, carefully scrape off the adhesive film from the solder joint connection area on the back of the new edge contact. (See Figure 3)
   Caution: Scrape off the epoxy backing only from the joint connection area. When handling the replacement contact, avoid touching the epoxy backing with your fingers or other materials that may contaminate the surface and reduce the bond strength.
10. 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 bonding. (See Figure 4)
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 5)
    Note: Allow the edge contact to overhang the edge of the circuit board.
12. Select a bonding tip with a shape to match the shape of the new edge contact.
    Note: The bonding tip should be as small as possible but completely cover the entire surface of the new edge contact.
13. 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 edge contact. Apply pressure as recommended in the manual of the repair system or repair kit for 5 seconds to tack the contact in place. Carefully peel off the tape.  
    Caution: Excessive bonding pressure may cause measling in the circuit board surface or may cause the new contact to slide out of position.
14. Gently place the bonding tip directly onto the contact. Apply pressure as recommended in the manual of the repair system or repair kit for an additional 30 seconds to fully bond the contact. The new edge contact is fully cured. Carefully clean the area and inspect the new edge contact for proper alignment.
15. 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. 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.
16. Remove the tape and clean the area.
17. 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 6)
18. 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.
    Caution: Some components may be sensitive to high temperatures.
    Note: Additional epoxy can be applied around the perimeter of the new edge contact to provide additional bond strength.
19. Apply surface coating to match prior coating as required.

Evaluation

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

Images

Edge Contact Repair, Film Adhesive Method

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

Select a replacement contact that matches the missing contact.

Scrape off the adhesive bonding film from the solder joint area on the back of new contact.

Cut out the new edge contact. Cut from the plated side.

Place the new edge contact in place using high temperature tape.

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

Completed repair.