Hey Jason,
I don't know of anyone who's actually done this, but we do also have a passive-cooled concept for our new digitiser board (loosely based on ROACH2). We've been thinking about a prototype that'd essentially be turning a ROACH2 board upside-down and bolting it onto a giant metal plate that's been appropriately milled out of a solid chunk of alu. The FPGA, PPC, QDR and other hot bits would make contact with the plate and use it as heatsink. The other high-profile parts (RAM DIMM, for example) needs holes or cavities milled out the alu.
Talk to Brent Carlson at DRAO (Canada). The EVLA correlator boards have a massive heatsink with a 3D profile machined on the PCB-side to accommodate the various heights of the devices on the board. Verification of the installation of the heatsink involved using an IR camera to view the rear side of the board to look for "hot spots". The EVLA boards are huge. Installation of a heatsink on your digitizer board should not have to be as complicated :) Cheers, Dave
