Why Oil Made The System Crash
In your article concerning the vegetable oils you wrote:
"Our initial attempts had shown that the poured oil sporadically led to crashes. The cause was also quickly found: The processor base together with the CPU and the heat sink had to be made impermeable to the liquid. Quite a bit of labor and time are necessary for this, since just like for the case, we first had to use special glue and then silicon. After successful sealing, the system works without a hitch."
We have the following explanation for this phenomenon: On the motherboard in the area of the CPU base, the oil is responsible for increasing the capacitive resistance between the individual wiring. In short, the oil acts as a dielectric material. Since very high frequencies occur on the motherboard, the capacitive resistance goes down. Accordingly, this then influences (or tampers with) the digital signals, particularly in the area of the CPU base. After all, 939 pins are located there in a very tight space. I believe you're on the right track, as proven by your experiments.
I'd like to offer this additional information: Vegetable oil is primarily a triglyceride. What this means is it's primarily a big molecule that consists of a glycerine [compound] holding onto three long-chain ester groups. This makes for a nice non-conductive medium that's fairly stable and readily available. However, at high temperatures this triglyceride will lose one, or more of its ester groups, which are then referred to as free fatty acids. These free fatty acids have vastly different dielectric properties, and (I'm assuming) a higher conductivity. I postulate that the higher temperature immediately surrounding the processor, and thus the pins, is increasing the concentration of free fatty acids, until a suitable conductivity exists to afford an errant discharge between pins. While the immediate fix is to seal off the processor/pin sockets/pins from the oil, I can't help but think that over time, the free fatty acid concentration may increase throughout the system, thus lowering pH, and increasing conductivity. This may give rise to the necessity for an oil change, or buffering of the acids with a material that would not increase the dielectric properties of the medium. I don't know how much time this lowering of the pH by vice of the free fatty acids (FFA) would take, but a calculation of the watt-density of the hottest parts acting on the volume of oil would be able to estimate the FFA concentration increase, and thus the pH decrease. Then again, this increase may take a year - or it may take a millennium - so it might be a moot point for the system as a whole.
Ed's Experiences With Liquid-filled Electronics
Nice work Frank.
Just a few comments from someone that has worked on a lot of liquid filled electronics. Water would work, but:
1. As you learned, you must protect all high frequency areas
2. You need continuous demineralization treatment. You need to keep the resistivity of the water high.
Better than vegetable oil would be white mineral oil (baby oil without the smell). Vegetable oil and auto oil will both attack many plastics and rubbers over time. There are some exotic fluids, but mineral oil or a synthetic with no lubricant additives is the best. And they are very clear.
Good Luck, Ed Blessman