I think
@hallux was referring to the fact that the damage to that board looks like it could have come from a typical welding arc, not the fact that it was soldered with too hot of an iron or other tool.
A while back, I changed the PRAM batteries on my Mac II board. Unfortunately, my board was one of the early ones for this model that had the batteries soldered to the board. In addition, it is one of a very Mac models that requires a working PRAM battery to boot(many will not boot with a dead battery installed, but are perfectly content to boot with no battery). In any case, I had no issue with getting the old batteries off and new ones in place(once I found the batteries with soldered leads in China). As things go, though, it's a pretty simple repair as the solder leads go all the way through the board.
Unfortunately, that board had other issues and I ended up replacing it completely(with a new in box Apple service part!). There was actually a service bulletin issued on the early Mac II boards that any which came in for repair with soldered batteries should have them replaced with a battery holder, and my replacement board had such a holder.
Now that I have a working Mac II, I want to pull an
@eyoungren and connect 6 monitors to it. I have enough NuBus video cards to make it happen, although I need to set up the space to do it. System 6 actually handles multiple monitors quite elegantly-the control panel is fundamentally unchanged even in Sierra(albeit it's been "prettied up" a lot from 1980s aesthetics and added a few features) and with some of the cards I have I can get 24 bit color at 1024x768. I'd consider that impressive for a 1986 computer, although you'd have been well into 5 figures to do it then(I think a basic system with a 4-bit color card and a 12" Trinitron was right at $10K) and I also don't think some of my cards were even on the market until closer to 1990.
All of that aside, I've also repaired key switches on the Apple Extended keyboards, a process which requires unsoldering the switch from the board. These are single layer boards with big traces, so fortunately they're also relatively easy.