PCB Microsurgery Puts The Bodges Inside The Board

PCB internal bodge

We all make mistakes, and there’s no shame in having to bodge a printed circuit board to fix a mistake. Most of us are content with cutting a trace or two with an Xacto or adding a bit of jumper wire to make the circuit work. Very few of us, however, will decide to literally do our bodges inside the PCB itself.

The story is that [Andrew Zonenberg] was asked to pitch in debugging some incredibly small PCBs for a prototype dev board that plugs directly into a USB jack. The six-layer boards are very dense, with a forest of blind vias. The Twitter thread details the debugging process, which ended up finding a blind via on layer two shorted to a power rail, and another via shorted to ground. It also has some beautiful shots of [Andrew]’s “mechanical tomography” method of visualizing layers by slowly grinding down the surface of the board.

[Andrew] has only tackled one of the bodges at the time of writing, but it has to be seen to be believed. It started with milling away the PCB to get access to the blind via using a ridiculously small end mill. The cavity [Andrew] milled ended up being only about 480 μm by 600 μm and only went partially through a 0.8-mm thick board, but it was enough to resolve the internal short and add an internal bodge to fix a trace that was damaged during milling. The cavity was then filled up with epoxy resin to stabilize the repair.

This kind of debugging and repair skill just boggles the mind. It reminds us a bit of these internal chip-soldering repairs, but taken to another level entirely. We can’t wait to see what the second repair looks like, and whether the prototype for this dev board can be salvaged.

Thanks to [esclear] for the heads up on this one.

23 thoughts on “PCB Microsurgery Puts The Bodges Inside The Board

  1. Wow! #1 having the ability to mill anything at that scale.
    Wow! #2 having the ability to mill fractional depths of a PCB layer
    Wow! #3 removing the PCB from the mill and returning to the same spot to mill some more at those tiny distances
    Wow! #4 soldering the tiny jumper
    Wow! #5 filling the tiny hole with epoxy.

    I am in awe.

  2. Seeing the first picture that shows the scale is a real Wow moment.

    We have a product here called solder wick (generically?) I use Chemwick, it would have been good to mop up the excess solder on the USB pad. It’s like the copper braiding of a shielded cable with (or without) a bit of flux added. The one with flux is far superior.

  3. It’s all about the tools. If you’ve got a FIB (focused ion beam) rework station, it makes this setup look like stone knives and bearskins. And having the tools that this guy has makes common hobbyist tools look like stone knives and bearskins. Of course, the coarser your tools, the better your skills need to be to get the job done. This is very impressive work.

    1. That’s within the territory of milling into the top of a chip package and inserting jumper wires to access data in “inaccessible” registers or glitch power supplies for a portion of a cpu.

      1. This is actually how Apple independent repair works Today due to DRM locking hardware to stored data:

        Long screw damage = multilayer board microsurgery


        ripped BGA pads on the CPU/NAND itself? microsurgery to dig it up


        blowing a short inside the CPU


        There was also one where you CNCed into the CPU to remove a short, but cant find the video now :(

  4. Really love to know how long such a repair takes – seems like one of those repairs it actually makes no sense to bother with except as practice or for fun. Really damn good stuff though, and great production quality on the images so you can really see as a newcomer to the PCB at a glance what you are actually seeing, and what it should be.

    1. Did you follow it up with a joke that if the posts get any longer you should stop posting them on twitter? Or just stop using twitter period?

      Nice work, though. I did something similar but a lot less impressive on a macbook that had the fan connector knocked off the board. Sharpened up my multimeter probes and found alternate soldering spots based on continuity readings after boring out the area beneath the connector footprint. I heard it worked flawlessly until the computer died for unrelated reasons. It’s hard work, but very satisfying.

      I’m curious why Femtoduino wanted this one prototype to be bodged when they knew what the problem was, or did they not? Why not just make new boards that weren’t shorted? Surely it would be cheaper than getting you to go through all this hassle?

    1. I can understand the pain of “not working and nobody knows why”
      A few days of micro surgery are annoying but well spent if this resolves the issue. Looks like this can be a manufacturing defect that is hard to prove even with xray.

      We’ve had cases where a board house claims “sure we can do pcbs for 0.4mm BGA pitch” – and half a year later you are in a dispute why the prototype boards are not working

  5. It’s fantastic work, but two things strike me as funny or odd. The first is that I just don’t get Twitter as a means to communicate things like this. It reads like stream of consciousness when people try to string tweets together, and this is one of the better ones.

    The second thing though is that with all these skills, Andrew didn’t immediately think “Huh, this is a 1/32″ board” when he picked it up. That’s the first thing I notice when I pick up a circuit board. Not so much a criticism, as an observation that everyone’s different.

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