4.7.6 Surface Mount Pad Repair, Film Adhesive Method, Butt Joint Method
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Outline
This method replaces damaged surface mount pads with new adhesive-backed dry film pads. The new pads are 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 surface mount pads. The new pads are fabricated from copper foil. They are available in many sizes and shapes and are generally supplied solder plated.
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.
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| Kits and Systems
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Master Repair Kit
Kit to repair circuit board damage including pads, lands, conductors and base material.
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| Tools and Materials
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Bonding Film
Dry film adhesive used to bond lifted lands, pads and conductors.
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Bonding Iron Tips
Used with a Bonding Iron to heat, cure and bond adhesive backed Circuit Frames.
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Circuit Tracks
Copper conductors to repair circuit board damage including traces and conductors.
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Cleaning Brushes
Disposable brushes for solvent cleaning and application of coatings.
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Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.
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| Additional Items and Supplies
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Cleaner
General purpose cleaner for removing contamination.
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Microscope
Precision microscope with stand and lighting for work and inspection.
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Oven
General purpose oven for drying, baking and curing epoxies.
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Soldering Iron
Properly maintained soldering iron and properly sized soldering iron tips.
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Tweezers
Multiple sizes and tip configurations of tweezers for various small parts handling needs.
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Wipes
Nonabrasive, low-linting wipes for cleanup.
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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.
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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.
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Circuit Bond has a working pot life of 30 minutes. It should not be mixed until ready to use. |
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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. |
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Cut a corner off the package and squeeze all the contents into a Plastic Cup. Stir the contents to ensure it is thoroughly mixed. |
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Circuit Bond may contain bubbles from the mixing process. If needed, use a vacuum system to remove bubbles. |
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Color Agent can be mixed in with Circuit Bond to match surface colors if desired. |
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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 |
| Packaging | 2 gram pre-measured packages |
| Mix ratio | 4 parts resin to 1 part hardener |
| Mix Ratio by Weight (R/H) | 100/25 |
| Color | Clear, transparent |
| Pot life | 30 minutes |
| Cure cycle | 24 hours at room temp (25 °C) or 4 hours @ 65°C |
| Thixotropic Index | 1 |
| Specific Gravity | 1.20 |
| Percent Solids | 100% |
| Viscosity (after mixing) | 2000 cps |
| Operating temperature range | -55°C to 135°C |
| Hardness | 88 Shore D |
| Lap Shear, Alum to Alum | 1100 psi |
| Glass Transition Temperature, Ultimate | 92°C |
| Coefficient of Expansion, cm/cm/°C | 6 E-05 |
| Dielectric strength | 400 volts/mil |
| Dielectric Constant, 1KHz@25°C | 4 |
| Shelf Life | 6 months minimum |
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Circuit Tracks
Circuit Tracks are rectangular-shaped conductors made of 99.9% pure CDA 11000 copper. These rectangular ribbons closely conform to the original conductor dimensions. The replacement Circuit Track is bonded in place using epoxy.
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Size |
| 115-5204 |
115-5204 Circuit Track, .002" x .004" (.051 mm x .102 mm) |
| 115-5205 |
115-5205 Circuit Track, .002" x .005" (.051 mm x .127 mm) |
| 115-5206 |
115-5206 Circuit Track, .002" x .006" (.051 mm x .152 mm) |
| 115-5208 |
115-5208 Circuit Track, .002" x .008" (.051 mm x .203 mm) |
| 115-5210 |
115-5210 Circuit Track, .002" x .010" (.051 mm x .254 mm) |
| 115-5312 |
115-5312 Circuit Track, .003" x .012" (.076 mm x .305 mm) |
| 115-5315 |
115-5315 Circuit Track, .003" x .015" (.076 mm x .381 mm) |
| 115-5520 |
115-5520 Circuit Track, .005" x .020" (.127 mm x .508 mm) |
| 115-5530 |
115-5530 Circuit Track, .005" x .030" (.127 mm x .762 mm) |
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Images and Figures
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Damaged Surface Mount Pad
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Figure 1: Remove the defective pad and remove soldermask from the connecting circuit.
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Figure 2: Select a replacement pad that matches the missing pad.
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Figure 4: Place the new pad in position using high-temperature tape.
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Figure 5. Place the circuit board on a PCB holder and bond the new pad using a Bonding System.
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Figure 6: Place a Circuit Track in poisition for soldering.
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Figure 7: Completed repair.
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Procedure
- Clean the area.
- Remove the defective pad and a short length of the connecting circuit. (See Figure 1)
- Use a knife and scrape off any epoxy residue, contamination, or burned material from the board surface.
- Scrap any solder mask or coating from the connecting circuit. (See Figure 1)
- 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 pad on the board surface must be smooth and flat. If internal fibers of the board are exposed, or if there are deep scratches on the surface, they should be repaired. Refer to the appropriate procedure.
- Select a replacement surface mount pad that most closely matches the surface mount pad to be replaced. If a special size or shape is needed, they can be custom fabricated. (See Figure 2)
Note: New surface mount pads are fabricated from copper foil. The foil is plated on the top with solder, and an adhesive bonding film is applied to the bottom.
- Cut out and trim the new pad. Cut out from the plated side. Cut the length of the connecting circuit so it butts up to the connecting circuit on the circuit board surface.
Note: A small copper Circuit Track jumper soldered to the traces will complete the electrical connection in a later step.
- Place a piece of High-Temperature Tape over the top surface of the new pad. Place the new pad into position on the circuit board surface using the tape to help in alignment. (See Figure 4)
- Select a bonding tip with a shape to match the shape of the new pad. See the bonding tip chart in the replacement parts section of the manual provided with the repair system or repair kit.
Note: The tip used for bonding should be as small as possible but should completely cover the entire surface of the new pad.
- Position the circuit board on a PCB holder so it is flat and stable. If a bonding system is used, align the tip. Gently place the hot bonding tip onto the High-Temperature Tape covering the new pad. Apply pressure as recommended in the manual of the repair system or repair kit for 5 seconds to tack the new pad in place. Carefully peel off the tape. (See Figure 5)
Caution: Excessive bonding pressure may cause measling in the circuit board surface or may cause the new pad to slide out of position.
- Gently place the bonding tip directly onto the new pad. Apply pressure as recommended in the manual of the repair system or repair kit for an additional 30 seconds to bond the pad fully. After the bonding cycle, remove the tape used for alignment. The new pad is fully cured. Carefully clean the area and inspect the new pad for proper alignment.
- Place a short length of Circuit Track in position over the top of the connecting circuits. Hold in place on each side with high-temperature tape. (See figure 6.)
- Apply a small amount of liquid flux to the overlap joint connection areas and solder the connections. Use minimal flux and solder to ensure a reliable connection.
- Trim the excess Circuit Track.
Caution: When trimming any excess Circuit Track, avoid damage to the circuit traces.
- Mix epoxy and coat the lap solder joint connection. Cure the epoxy per Procedure 2.7 Epoxy Mixing and Handling.
Note: Additional epoxy can be applied around the perimeter of the new pad to provide additional bond strength.
Caution: Some components may be sensitive to high temperatures.
- Apply surface coating to match prior coating as required.
Evaluation
- Visual examination.
- Measurement of new pad width and spacing.
- Electrical continuity measurement.
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Procedure for reference only.
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