Reworking an Internal Connection at a Via Hole

This procedure was used to modify a batch of circuit boards with a signal error at a via-hole location. A via hole on this multilayer circuit board was mistakenly connected to layer nine when it should have been connected to layer 15.

This is genuine micro-surgery, but it can be done reliably in the hands of skilled and trained technicians.

Here is how we do it.

1. On the primary side, we completely drill out the plating in the via hole to isolate the hole from layer nine, but leave the perimeter of the surface pad and the connection to the surface pad intact.
2. On the secondary side, we perform a controlled depth mill to expose the layer fifteen ground plane. You can see the ground layer as a crescent shape in the photo.
3. On the secondary side, we solder a wire to the exposed layer fifteen and route the wire through the circuit board.
4. We solder the opposite end of the wire to the via pad on the primary side.
5. On the secondary side, we fill and seal the exposed plane using high-strength epoxy.
6. On the primary side, we seal the attached wire connection using high-strength epoxy.

This task would be very challenging, if not impossible, for most, but not for properly equipped and skilled technicians. Another hearty handshake and a pat on the back to the super techs at Circuit Technology Center who completed this rework.