Damaged Conductor Repair - Like Circuit Brain Surgery

Figure 1: X-ray of subject location with out damage.

WOW! A batch of circuit boards were improperly and dramatically drilled in a spot they weren't supposed to be drilled in. That can be a tough error to recover from when applied to today's complex boards.   

Figure 1 is an x-ray of one of these boards before the inadvertent drilling.  Figure 2 is an x-ray of what this location looked like post-drill. As a result the customer found himself with a scrap heap of worthless product where once there were very valuable and difficult to replace printed circuit boards.

What to do? Here's the quick and dirty. As you can see by the x-rays, the area drilled has many circuits running through it.  Including the top and bottom surfaces, there are four layers of circuitry running through the board.  Still it can be repaired and the approach is like the answer to the old saw "How do you eat an elephant?" 

Figure 2: X-ray of same area after drill damage.

 

"One bite at a time."  That is we have to rebuild the location, one connection and one layer at a time.

The first step - if you can believe it - is to drill again (Figure 3). We drill to make the hole a common size so we can manufacture a replacement plug that will be a uniform shape for all the holes in the batch of circuit boards.  Additionally we drill to make the hole walls a consistent surface for positioning and adhering the repair material.

With each hole is a consistent size we can begin to re-construct the internal stack up. A specially machined plug is inserted and adhered into the hole to replace the core of the board. Once that piece is cured in place the internal circuitry that occupied the space on either side of the core is replaced.

Figure 3: Hole re-drilled.

Every circuit in the board must be individually exposed, tinned and connected using copper circuit track material.  You can see the material by following this link http://www.circuitmedic.com/products/201-3130.shtml.

The circuits also must be insulated from the power and ground planes that may run through the area. After the internal traces were connected and tested, each open side of the plug was filled to the top and bottom surface with high strength thermo setting epoxy.

Figure 4: Replaced internal conductors.

Figure 5: Replaced internal conductors and some surface conductors.

Figures 4 and 5 show the specially manufactured dowel plug adhered in-place and the replacement circuit tracks either laying on the dowel surface (internal traces) or suspended in place (top and bottom traces). In this case the circuit tracks for all layers were connected prior to the epoxy fill.

Finally top and bottom surfaces were blended cosmetically to complete the repair.  Figures 6 and 7 show the bottom and top sides of repaired boards.  Sorry, these pictures are of other repaired units, but I hope you'll get the point.

Figure 6: Completed board.

Figure 7: Completed repair.

That's it! Believe me that's one tough repair and post repair testing has proven that the repaired units work just fine.

We're mighty proud of our team of techs who had the patience, skill and discipline to undertake such a challenging project and do so successfully.

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