Brad, We used a crude but effective scheme to fly a roach I on high altitude balloon in Sept 2011. Since weight for us is not a big issue, the approach is to use a thick sheet of aluminum plate (~0.25 in thick) and larger than the roach assembly as a heat spreader. We mounted the roach board upside-down using spacers to clear parts and connectors. (Xilinx heatsink and fan removed) To contact the Xilinx chip and the PPC, we machined aluminum blocks matching the chip footprint and matching the chip to plate clearance (within a few mil). Any gaps were accommodated by Berquist thermal pad material. We also put a similar heatsink on the ADCs using a copper strap and thermal pad. We put spring loaded fasteners in the holes in the roach board near the Xilinx chip to prevent the board from warping away from the heatsink block in flight.
We build up a 28VDC ATX-type power supply using Vicor modules. These have a high power density, are easy to heat sink and we've used these type on many balloon flights. Finally, we put a metal cover over the entire roach and power supply assembly. Heat from the heat spreader plate was dumped through small radiator plate that extended outside the gondola insulation. In flight, the FPGA internal sensor read about 65C peak during the day at float (~4hPa) and at night cooled to ~20C. Hope this helps a bit. Bob Stachnik - * Robert A.Stachnik, M/S 183-401| [email protected] * Jet Propulsion Laboratory, | Office: (818) 354-1921 * 4800 Oak Grove Drive, | Cell: (818) 653-8738 * Pasadena, CA 91109-8099, USA | FAX: (818) 354-5148 ********************************************************************** ________________________________________ From: Jason Manley [[email protected]] Sent: Tuesday, April 16, 2013 4:37 AM To: dana whitlow Cc: Steve Maher; Vaughan Moss; Casper Lists Subject: Re: [casper] Roach Conduction Cooling > Merely dunking things in liquid will just get you hot liquid. And I'd be > concerned > about the chip packages' leak integrity. Excellent point. In fact, the Xilinx packages have breather holes that prevent us from washing the boards after manufacture. So I'd be very nervous about this. > My point is, don't forget the radiator. Then ask, perhaps, "Can I just > attach the > chips to the radiator?". Perhaps this is already what Jason is getting at, > but he > didn't say how his "heatsink" was going to dispose of the heat. Yeah, big fins on the other side of the alu! You'd have to run the numbers to see how big and how many fins you'd need at altitude/thin air. Jason
