For that SEM cathodoluminescence gizmo I mentioned in the distributed attenuator thread, I need to cool a multi-pixel photon counter (MPPC) down to about -10C. It's on the end of a piece of aluminum with about 5 K/W thermal resistance, so I need to keep the heat leak to a minimum or I'll run out of Q-dot.
So I'm sort of breathing on the cold plate design. Silver epoxy is a good option, because it eliminates the heat leak through the screws, but I really want to put a compressive preload on the TEC, because that improves its shear strength and shock resistance.
One traditional approach is to use nylon screws. Switching from #2 stainless to #6 nylon reduces the heat leak by 20x. However, nylon isn't good in a vacuum, because it outgasses, dries out, and falls apart. (At least it's reasonably cheap--a nickel a screw or thereabouts.)
I looked at other plastic screws at McMaster-Carr, and the price difference is fairly shocking--even screws made of some totally garden-variety plastic such as PVC cost dollars apiece, and just forget Vespel or any of the other plastics you really want.
Anybody got a source of plastic screws other than nylon?
Cheers
Phil Hobbs