and hiding under the solder mask. Nasty.
Obviously the first step is to remove the affected components and neutralize the caustic ...
I usually use 25% vinegar acid and wait until the bubbling stops (which is an indication of the reaction having finished).
When done, the pcb goes into the ultrasonic. Solder mask is removed with a fiberglass pen, any caustic that has crept under the solder mask can be discovered and any hidden corrosion can be removed.
Then it's repairing traces and redoing those little through holes and the contacts ...
A Bungard press is great for that.
After several hours of work the board was back in operations ...
Tools used: scalpel, fiberglass pen, soldering iron and desoldering station, ultrasonic, neutralizing agent (vinegar acid), compressed air, very fine copper wire, bungard press, DMM (for continuity checks), Oscilloscope (for checking the signals at the probe points and I/Os)