4.6.1 Edge Contact Repair, Epoxy Method

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Printed Board Type: R/F/W/C
Skill Level: Advanced
Conformance Level: Medium
Revision: C
Revision Date: Jul 7, 2000

OUTLINE

Damaged Edge Contact

This method is used to replace 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 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 either plain copper, solder plated or nickel and gold plated. If a special size or shape is needed it can be custom fabricated. 

ACCEPTABILITY REFERENCES
IPC-A-600 2.0	Externally Observable Characteristics
IPC-A-610 10.0	Laminate Conditions
PROCEDURE REFERENCE
1.0	Foreword
2.1	Handling Electronic Assemblies
2.2	Cleaning
2.5	Baking and Preheating
2.7	Epoxy Mixing and Handling
IPC7721 4.6.1	Edge Contact Repair, Epoxy Method

Figure 1: Remove the defective edge contact and remove solder mask from the connecting circuit.

TOOLS & MATERIALS
Bondintg System
Circuit Frames, Edge Contacts
Cleaner
Epoxy
File
Gold Contact Repair Kit
Knife
Flux, Liquid
Microscope
Oven
Tweezers
Solder
Soldering Iron
Scraper
Tape, Kapton
Wipes

PROCEDURE

1. Figure 2: Select a replacement contact that matches the missing contact.

   Clean the area.
   
   
2. Remove the defective edge contact and a short length of the connecting circuit. 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. Figure 3: Cut out the new edge contact.

   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 in 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. Figure 4: Place the new edge contact in place using Kapton tape.

   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 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 Kapton tape over the top surface of the new edge contact. Position the new edge contact on the circuit board surface using the Kapton tape to aid in alignment. (See Figure 4).

    
    NOTE
    Allow the edge contact to overhang the edge of the circuit board. Leave the Kapton tape in place during the bonding cycle.
    
    

12. Figure 5: File overhanging piece of new edge contact to blend with existing bevel.

    Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.

13. CAUTION
    Some components may be sensitive to high temperature.
    
    

14. After the epoxy has cured, remove the Kapton 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.
    
    

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. Kapton 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. Figure 6: Completed repair .

    Remove the Kapton 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 5).
    
    
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.
    
    
19. If plating is required refer to appropriate procedure.
    
    
20. Apply surface coating to match prior coating as required.
    
    

EVALUATION

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