Apologies in advance for the noobness of this post - but I am genuinely curious about what might have happened here.

I got a 20L ultrasonic cleaner for various projects, including PCB cleaning and restoration. Of course before dumping anything in that I care about, I reached into my “non functional” pile, and pulled a couple of expansion cards, as well as a dead Intel VC820 (as in, dead dead, no obvious damage, but does not power up at all).

After some pretty incredible results, I went for it and cleaned a few working parts, including an nForce2 motherboard. Everything still worked great and now look great as well.

A day later however, I looked at the VC820 and the solder is doing..something! A white powder/paste of sorts has emerged from the surface mounted components. Interestingly, nothing on the backside of the board.

Cleaning process for everything was:
- Distilled water and 5% Elma Tec A1 PCB cleaner, at 60C
- Degas
- Sweep, 2 minutes cleaning per side
- post cleaning, 99% IPA bath for approximately 10 seconds
- initial dry using air compressor
- 24 hour dry time before any reassembly

I can clean the the substance using IPA and a brush or cotton swab, but, again I am very interested to understand what this might be.