I am working on restoring an old Intel Motherboard with a 478 PGA Socket, an accompanying Intel Pentium 4 Prescott, and various expansion cards that have some form of dry mold coating it. I am working on cleaning the surface level mold off with electronics grade isopropyl alcohol but the only solution I could think of to ensure the board mold free would be to completely submerge it in the isopropyl alcohol. I know many people that restore retro electronics do clean PCB's that way but I have never actually done that myself. Are there any pitfalls of submerging a board in a cleaning solvent?
For what it's worth, on moldy 8-bit machines I've often used a fungicidal product on the Danish market called Rodalon which I think may be more or less equivalent to Lysol, but you can look it up for a break down of the component chemicals.
While IPA has good cleaning properties, I've found that it can still be hard to get rid of the "basement" smell after mold, and the Rodalon solution cures that.
It can be sprayed on but to be most effective I prefer to submerge the PCBs or cases in a solution of destilled water and Rodalon and brush the board carefully, fx with a toothbrush. The caveat is the same as for any kind of deep board washing: it should only be done if there are no components such as relays or other components that could react poorly to or retain water.
Rinse in clean destilled water, blow dry, rinse in IPA to help displace the water, and dry again carefully with warm air, especially around switches, under ICs and other places that could retain water.