Unique Ground Plane Transplant Repair

In the world of rework and repair, there can never be a standard procedure for every emergency. Things can happen quickly, and there can be an urgent need to go above and beyond the recognized standards outlined in IPC and other industry guides.

These kinds of situations demand innovation and new processes. So, we've had many occasions to work closely with our customers and partners to create leading-edge solutions through the years.

In this example, we developed a procedure to repair large ground plane voids. Again, we worked hand-in-hand with a customer who provided critical reliability data for the completed repair, confirming the repair process was sound.

Several challenging and unique approaches were attempted before a final process was certified. Although this is a bit extreme, it represents an example of the relationship we have with many of our customers developing leading-edge circuit board repair processes.

Outline
This method is used to repair damaged surface ground planes. The damaged areas are repaired with dry film adhesive-backed copper foil disks. They are bonded to the circuit board surface using a bonding press.

Instructions

Damaged Surface Plane

Clean the area.
Secure the circuit board in a Precision Drill/Milling System with a microscope available for viewing. Use an end mill slightly larger than the void in the surface ground plane and make a counterbore through the surface plane only. Do not mill into the laminate material; you may expose inner layer circuits.
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 the appropriate procedure.
Figure 1: Milled area to remove damaged foil .

Select a replacement adhesive-backed disk that matches the end mill size used to make the counterbore. 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.

Figure 2: Transplant new foil disk into milled out area.

Position the circuit board to be flat and stable. 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 for 5 seconds to tack the adhesive-backed disk in place. Carefully peel off the tape.
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 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.
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.
Remove any excess solder Using the "Blade" shaped soldering tip and desolder braid. Clean the area.
Using the Electric/Hand Eraser, clean and buff the soldered area to blend the repair to the circuit surface.

Figure 3: Solder tin the area and blend in.
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 further as necessary. (See Figure 3)
Clean the area.
Blend the surface using an appropriate buffing material.

Another common defect was solved using a not-so-common solution.

Several members of the Circuit Technology Center team contributed to this feature story.