In a past life..... I had to repair an IBM PS/2 Model 50 for a customer, who used it to run his industrial controls (that I serviced).
I got a replacement motherboard, and sometime about 10pm changed it out. IBM in their infinite wisdom used slotted head screws to attach the motherboard to chassis. I slipped, and busted thru about a dozen really, really fine traces.
Exacto knife at the ready, I was able to clean up the spaces between the traces. Then I used some really fine... probably 600 grit paper to expose the copper of each trace on each side of the break. Fluxed and tinned the whole mess at once. Then grabbed a spare modular phone cable and broke it down to individual strands of ....I dunno 40gauge or so wire. Really fine stuff. Tin one end of the fine wire. Solder to the tinned trace. Stretch it across the break. Solder to the other side of the break. One down... eleven or so more to go. I staggered the places I soldered. Got it all done, cleaned it up with alcohol and made sure nothing was touching. Fired up fine. Since it seemed to work, power down and cover the repair with some dope to make sure it sort of got insulated and would remain undisturbed. Worked for years until they upgraded to something newer.
That repair will stick in my memory till I croak. I don't think there was anything special about my soldering setup, although I've used PACE equipment for decades. I'm guessing it was just a medium tip at perhaps a bit higher than normal heat to be quick in/out things.