4.2.7 Conductor Repair, Surface Plane, Film Adhesive Method
Outline
This method is used to repair damaged circuit surface planes. The damaged areas are repaired with dry film epoxy, adhesive-backed copper foil disks. They are bonded to the circuit board surface using a bonding press or bonding iron.
Caution: It is essential that the board surface be extremely smooth and flat. If the baseboard is damaged, see the appropriate procedure.
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.
Kits and Systems
Professional Repair Kit
Kit to repair damaged pads, lands, conductors, base material, and plated holes.
Master Repair Kit
Kit to repair circuit board damage including pads, lands, conductors and base material.
Land/Pad Repair Kit
Kit to repair circuit board damage including lands and pads.
Circuit Bond Kit
Includes clear, low viscosity, superior strength epoxy for circuit board damage repair.
Circuit Bonding System
System to thermally bond replacement conductors, BGA pads, and SMT pads.
Flex-Rack PCB Holder
Sturdy holder supports PCBs for rework, drilling, pad repair, and positioning.
Precision Tool Set
Nine precision-crafted tools for detailed circuit board work.
Tools and Materials
Abrader
Mild abrasive for removing oxides and contaminants.
Scraper, Curved Tip
Hardened stainless steel tip for scraping solder mask and removing defects.
Additional Items and Supplies
Cleaner
General purpose cleaner for removing contamination.
Desolder Braid
Woven copper wire designed to wick solder from surfaces and holes.
End Mills
Designed for end cutting and hole boring.
Microscope
Precision microscope with stand and lighting for work and inspection.
Milling Machine
Use for precision milling of circuit board materials.
Oven
General purpose oven for drying, baking and curing epoxies.
Precision Drill
Precision drill press for accuracy and controlled depth drilling.
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.
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.
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
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
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
Damaged Surface Plane
Figure 1: Milled area showing removal of damaged surface conductor foil.
Figure 2: The transplant conductor foil in place.
Figure 3: Bond the new adhesive backed disk using a Bonding Iron.
Figure 4: The transplant conductor foil bonded, soldered and blended to the surrounding surface.
Procedure
Clean the area.
Secure the circuit to a Precision Drill/Milling System with a microscope available for viewing. Use an end mill slightly larger than the void in the surface plane and make a counterbore through the surface plane only. Do not mill into the laminate material, you may expose inner layer circuits.
Note: Several adjacent counterbores may be required to fill larger areas.
Clean the area with solvent.
The area for the new Adhesive Backed Disk on the board surface must be smooth and flat. If internal fibers of the board are exposed, or there are deep scratches on the surface, they should be repaired. Refer to appropriate procedure.
Select a replacement adhesive-backed disk that matches the size of the end mill used to make the counterbore. Note: The thickness should be selected to meet the requirements of the circuit board surface plane thickness.
With the adhesive-backed disk positioned film side up, carefully scrape off the adhesive film from the outer 0.005" of the disk diameter.
Position the adhesive-backed disk, film side down. Place a piece of High-Temperature Tape over the adhesive-backed disk, and position the adhesive-backed disk into the counterbore. Press the adhesive-backed disk into position. (See Figure 2)
Select a bonding tip with a shape to match the shape of the adhesive-backed disk.
Note: The bonding tip should be as small as possible but should completely cover the entire surface of the adhesive-backed disk.
Position the circuit board so that it is flat and stable. Gently place the hot bonding tip onto the tape covering the adhesive-backed disk. Apply pressure and heat as recommended in the manual of the Repair System or Repair Kit for 5 seconds to tack the adhesive-backed disk in place. Carefully peel off the tape. (See Figure 3)
Gently place the hot bonding tip directly onto the new adhesive-backed disk. Apply pressure and heat as recommended in the manual of the Repair System or Repair Kit for an additional 30 seconds to fully bond the new adhesive-backed disk. The new adhesive-backed disk is fully cured. Carefully clean the area and inspect the new adhesive-backed disk for alignment.
Note: Several adjacent counterbores may be required to fill larger areas.
Using flux and solder, carefully add a small amount of solder to a soldering iron with a "Blade" shaped tip, and flow solder over the repaired area.
Using the "Blade" shaped soldering tip and desolder braid, remove any excess solder
Clean the area.
Using the Electric/Hand Eraser, clean and buff the soldered area to blend the repair to the circuit surface.
Using High-Temperature Tape, mask off an area larger than the repaired area.
Using the abrasive pad, "lightly" buff the masked area to blend the repair to the circuit surface as necessary. (See figure 4)
Clean the area.
Final Finish
Blend the surface type using an appropriate buffing material or abrasive pad.
Matte and semi-gloss surfaces may require light abrasion in order to blend to the original surface finish type. High gloss will require polishing.
Remove any loose particles as necessary and clean the area.
