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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
Recommended for technicians with soldering and component rework skills and exposure to most repair/rework procedures, but lacking extensive experience.

Conformance Level - High
This procedure most closely duplicates the physical characteristics of the original, and most probably complies with all the functional, environmental and serviceability factors.

Acceptability References
IPC-A-600 2.0 Externally Observable Characteristics
IPC-A-610 10.0 Laminate Conditions
Procedure References
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
Kits and Systems
201-2100
Professional Repair Kit
Kit to repair damaged pads, lands, conductors, base material, and plated holes.
201-2400
Master Repair Kit
Kit to repair circuit board damage including pads, lands, conductors and base material.
201-5231
Circuit Bonding System
System to thermally bond replacement conductors, BGA pads, and SMT pads.
110-6380
Flex-Rack PCB Holder
Sturdy holder supports PCBs for rework, drilling, pad repair, and positioning.
201-6100
Gold Contact Plating Kit
Kit to repair and replate damaged gold edge contacts and pads on circuit boards.
201-4350
Repair Skills Practice Kit
Training kit to practice circuit board repair skills prior to testing for certification.
Tools and Materials
115-3210
Bonding Iron, 120 VAC
Delivers the optimal heat for curing adhesive bonding film.
CircuitMedic Part
Bonding Iron Tips
Used with a Bonding Iron to heat, cure and bond adhesive backed Circuit Frames.
circuit-frames
Circuit Frames
Circuit Frames
115-3302
Circuit Bond Epoxy
Clear, superior strength epoxy in two-compartment plastic packages.
235-3050
High Temp Tape Discs
High temperature polyimide tape discs, .50" diameter.
355-0614
Knife with #16 Blades
A must-have tool for precise cutting, scraping and trimming.
335-3197
Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.
Additional Items and Supplies
Cleaner
Cleaner
General purpose cleaner for removing contamination.
Microscope
Microscope
Precision microscope with stand and lighting for work and inspection.
Oven
Oven
General purpose oven for drying, baking and curing epoxies.
Solderinmg Iron
Soldering Iron
Properly maintained soldering iron and properly sized soldering iron tips.
Hot Plate
Tweezers
Multiple sizes and tip configurations of tweezers for various small parts handling needs.
Wipes
Wipes
Nonabrasive, low-linting wipes for cleanup.
Bonding Iron Tips
Bonding Iron Tips fit into the handheld Bonding Iron. The bottom surface of each Bonding Tip is used to apply heat and pressure to bond adhesive-backed replacement lands, pads, and edge contacts to a circuit board surface. The pressure/force listed is the recommended load in pounds to apply to the top surface of the replacement adhesive-backed pads, lands, and conductors. The load is based on the Bonding Tip surface area to meet the recommended load for Circuit Frames at 200 - 400 psi.
Part No. Size Pressure/Force
115-2801 115-2801 Bonding Tip, Tapered N/A
115-2802 115-2802 Bonding Tip, .080" (2.03 mm) Diameter 1.00 lbs
115-2803 115-2803 Bonding Tip, .120" (3.05 mm) Diameter 2.26 lbs
115-2804 115-2804 Bonding Tip, .040" x .060" 0.48 lbs
115-2805 115-2805 Bonding Tip, .080" x .120" (2.03 x 3.05 mm) 1.92 lbs
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
Packaging2 gram pre-measured packages
Mix ratio4 parts resin to 1 part hardener
Mix Ratio by Weight (R/H)100/25
ColorClear, transparent
Pot life30 minutes
Cure cycle24 hours at room temp (25 °C) or 4 hours @ 65°C
Thixotropic Index1
Specific Gravity1.20
Percent Solids100%
Viscosity (after mixing)2000 cps
Operating temperature range-55°C to 135°C
Hardness88 Shore D
Lap Shear, Alum to Alum1100 psi
Glass Transition Temperature, Ultimate92°C
Coefficient of Expansion, cm/cm/°C6 E-05
Dielectric strength400 volts/mil
Dielectric Constant, 1KHz@25°C4
Shelf Life6 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
4.6.2 Edge Contact Repair, Film Adhesive Method
Damaged Edge Contact.
4.6.2 Edge Contact Repair, Film Adhesive Method
Figure 1: Remove the defective edge contact and remove solder mask from the connecting circuit.
4.6.2 Edge Contact Repair, Film Adhesive Method
Figure 2: Select a replacement contact that matches the missing contact.

4.6.2 Edge Contact Repair, Film Adhesive Method
Figure 3: Scrape off the adhesive bonding film from the solder joint area on the back of new contact.
4.6.2 Edge Contact Repair, Film Adhesive Method
Figure 4: Cut out the new edge contact. Cut from the plated side.
4.6.2 Edge Contact Repair, Film Adhesive Method
Figure 5: Place the new edge contact in place using high temperature tape.

4.6.2 Edge Contact Repair, Film Adhesive Method
Figure 6: Bond the new edge contact with a Bonding Iron.
4.6.2 Edge Contact Repair, Film Adhesive Method
Figure 7: File overhanging piece of the new edge contact to blend with existing bevel.
4.6.2 Edge Contact Repair, Film Adhesive Method
Figure 8: Completed repair.

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. (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.
  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. 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.
  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 7)
  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.
Procedure for reference only.