deskthority

I have one of those PCB in a group buy damage:

The double-sided PCB has some keys (QWERT keys and some function keys) not working and I have identified that two traces of the circuits are damaged and broken, e.g. likely by the sharp pins of switches when inserted carelessly so the pins bent and scratched the surface of the PCB and took out a sand grain size trunk of the paint together with the circuit. The two damaged areas are right next to the insert of the pins for switches and a thick jumper cable will block the insertion of a switch.

For repair, I have to reconnect those thinner than hair traces. First,I scratched open both ends of the opened circuit so the copper underneath exposes. But then, my attempts to reconnect them were. Things I tried included applying flux and then trying to use just solder, but solder doesn't stick, despite the gap is ~<0.5mm and the total exposed length of copper on both ends is shorter than 5mm. I also tried soldering a hair-thin copper wire of about 5mm, but a single drop of solder when melt is way bigger than the whole thing of the wire and the scratched copper circuit area with the open circuit in the middle.

I have watched videos of circuit board repair with workers doing things with surgical precisions, but it can still be that the areas I need to fix are really tiny and my skill and knowledge is too much of a beginner.
I wonder what I can still try.

How would you approach such a repair?
I am in Germany by the way.

Conductive ink or solder rarely give a successful repair on tiny traces, especially on something like a keyboard where the PC board sees physical stress. In my experience the best fix is to follow the traces to the next solder pads and run a small wire from pad to pad (after the components or switches are installed). Avoid lead-free solder; rosin core 60/40 or 63/37 works best for PC boards.

Menuhin wrote: I have one of those PCB in a group buy damage:

The double-sided PCB has some keys (QWERT keys and some function keys) not working and I have identified that two traces of the circuits are damaged and broken, e.g. likely by the sharp pins of switches when inserted carelessly so the pins bent and scratched the surface of the PCB and took out a sand grain size trunk of the paint together with the circuit. The two damaged areas are right next to the insert of the pins for switches and a thick jumper cable will block the insertion of a switch.

For repair, I have to reconnect those thinner than hair traces. First,I scratched open both ends of the opened circuit so the copper underneath exposes. But then, my attempts to reconnect them were. Things I tried included applying flux and then trying to use just solder, but solder doesn't stick, despite the gap is ~<0.5mm and the total exposed length of copper on both ends is shorter than 5mm. I also tried soldering a hair-thin copper wire of about 5mm, but a single drop of solder when melt is way bigger than the whole thing of the wire and the scratched copper circuit area with the open circuit in the middle.

I have watched videos of circuit board repair with workers doing things with surgical precisions, but it can still be that the areas I need to fix are really tiny and my skill and knowledge is too much of a beginner.
I wonder what I can still try.

How would you approach such a repair?
I am in Germany by the way.

Thanks for your suggestions.

I tried lead-free solder in the past and that did not work for me on anything, and I am currently using rosin core solders.

Here is a photo of the PCB that needs to be repaired, the tiny black dots in the middle of the two red circles are the opened traces that need to be connected again.

These are the PCB trace repair technique videos that I talked about, while the trace in these demonstrations are still a bit wider than those I have to deal with above, these guys are equipped with microscopes and really fine soldering tips and many more tools and materials designed for the job:

If you want to make a jumper, what you do is actually run a new wire between the endpoints like Polecat said. These are the two wires you need to run. The top one on the switches I would do after the switches are installed. You can also just make the one with the board passthroughs use whatever pads each leads to on the other side.

Menuhin wrote: I tried lead-free solder in the past and that did not work for me on anything, and I am currently using rosin core solders.

FYI: Leaded/lead-free != flux type (rosin core / water soluble / no-clean)