Thanks for the feedback, 0xDEADBEEF and f95toli. Based on your advice and my own research, this is the solution I'm going with:
Ceramic LCC carriers from EverGreen Semiconductor:
http://www.evergreensemiconductor.com/ceramic-leadless-chip-carrier.html
PLCC sockets by 3M...
Hi f95toli, thanks for the reply!
Good call about the CMR carriers. At this point, I don't think I'll need non-magnetic carriers.
I decided to go for a carrier/socket solution because I want to be able to switch in and out samples quickly without disturbing them or having to re-bond them...
The quest continues.
I've been recommended to check out CMR's LCC carriers: http://www.cmr-direct.com/en/sample-mounting/cryogenic-sample-mounting/mpuck-system/mp-llcc20-nm The guy who recommended them says they work well in HV and down to cryo temperatures. However, he recommended against...
I'm looking for chip carriers and sockets that will work well down to 4 K. Most aren't rated below -70 C, but I know in the past I've seen sets used down to 1.6 K. (Wish I could remember what they were!) Does anyone have specific recommendations? Or general advice, plastic vs ceramic, etc...