4-17. Printed Circuit Boards - Continued
Follow the foil repair procedure in (2) below.
Foil Repair Procedure.
Choose a matching foil, copper, aluminum, wrought copper, or gold ribbon.
Measure the conductor width and select the proper size for repair.
Cut foil length 1/4 inch longer than the break.
Prepare surface to be repaired by solvent or abrasion.
Lap reflow solder along the center of the conductor.
Inject epoxy filler under repair foil with a hypodermic needle.
Clean residue from the repair area.
Recoat the solder joint with conformal coating.
Figure 4-44.5. Foil Repair
Conductor Repair Procedures for Multilayer Boards. Use the parallel gap welding technique to repair defective
printed circuit conductors on double-sided and multilayer boards. This method can be used to repair breaks on both inner
and outer layers. Refer to the procedure below:
Locate break and chisel or mill away base until enough conductor is exposed to perform a weld (0.1 inch of
conductor on each side of the break)
Clean conductor to a shiny color for a proper weld.
Select a gold ribbon the same width as the conductor being repaired (preferred material).
Position gold ribbon over the break.
Apply a spot weld on each side of break with a parallel gap welder.
Control the interelectrode spacing for consistent results.
2 Vary the spacing according to the materials and the bond to be produced.
3 Fit the electrodes tight against the work for good electrical and thermal conductivity.
4 Use a spacing at least 1-1/2 times the thickness of the upper material.
Change 6 4-46.3