Is it possible to repair corrosion on the PCB?

[Rico]

@Dave is right.
So the good news is that most probably your MCU is fine.
The bad news is that you will have to desolder switches to clean the mess.
As I’m quite used to this process I would desolder everything to clean the top side of the PCB cleanly.
But it is a time consuming process and you need to have a good desoldering pump.
I made an explanation of the process in this forum at the following link:

Changing key switches of your good old keyboard

Hi all, What I like about mechanical keyboard is of course the great typing feel but also the fact that they can be repaired quite easily. It is a quite unique situation in our 21st century were programmed obsolescence rules. So I slowly began to repair friend’s or colleague’s keyboard just for that reason, and convince them not to put their keeb in the trash. Here is a description of how I did to replace all switches on a colleague’s keyboard, a Das Keyboard 4 Professional for Mac. It may …