4.6.2 Edge Contact Repair, Film Adhesive Method

4.6.2 Edge Contact Repair, Film Adhesive Method

Printed Board Type: R/F/W/C
Skill Level: Advanced
Conformance Level: High
Revision: D
Revision Date: May 8, 2001

OUTLINE

Damaged Edge Contact

to the circuit board surface using a bonding iron or bonding press.

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 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.

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 4.6.2	Edge Contact Repair, Film Adhesive Method

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

TOOLS & MATERIALS
Bonding Iron
Bonding Tips
Bonding System
Circuit Frames
Cleaner
Epoxy
File
Flux, Liquid
Gold Contact Repair Kit
Knife
Microscope
Oven
Scraper
Solder
Soldering Iron
Tweezers
Wipes

PROCEDURE

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

Clean the area.
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).
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).
Figure 3: Scrape off the adhesive bonding film from the solder joint area on the back of new contact.

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 in 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).

NOTE
The new replacement edge contact may be trimmed from copper sheet.
Figure 4: Cut out the new edge contact. Cut from the plated side.

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.
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).
Figure 5: Place the new edge contact in place using Kapton tape.

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 5).

NOTE
Allow the edge contact to overhang the edge of the circuit board.
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.
Figure 6: Bond the new edge contact with a Bonding System.

Position the circuit board so that it is flat and stable. Gently place the hot bonding tip onto the Kapton 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. (See Figure 6).

CAUTION
Excessive bonding pressure may cause measling in the circuit board surface or may cause the new contact to slide out of position.
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. After the bonding cycle remove the tape used for alignment. The new edge contact is fully cured. Carefully clean the area and inspect the new edge contact for proper alignment.
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.
Figure 7: File overhanging piece of the new edge contact to blend with existing bevel.

Remove the Kapton 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 7).
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 temperature.

NOTE
Additional epoxy can be applied around the perimeter of the new edge contact to provide additional bond strength.
Figure 8: Completed repair.

Apply surface coating to match prior coating as required.