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.
Tools and Materials
Abrader
Mild abrasive for removing oxides and contaminates from conductive surfaces.
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.
Scraper
Hardened stainless steel tip for scraping solder mask and removing defects.
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.
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.
