do the chips really transfer more heat into the PCB than to the upper side?
Yes, they are designed this way. And you shouldnt put a heatsink on top. Yifu said this will have a negative effect instead.
Can anybody verify this?
On computer mainboards. (NB/SB , MOSFETS) or RAM you can cool with out problem from the top.
The differential temperature in one chip should be less than 1°C ... i can not image that this would have a negativ effect.
The only can explain the negativ effect throuhg wrong/to high mounting force. (so that the chip will break)
Regards
Finn
Hey guys, to all who are concerned about cooling from the other side of the PCB, please chill (pun intended) and study "thermal vias" - a common method to cool modest wattage surface mount components from the back of the board. Read up here and feel better:
http://www.electronicproducts.com/Thermal_Management/Heat_Sinks_and_Thermal_Materials/PCB-cooling_techniques_and_strategies_for_IC_packages.aspxBottom line: Don't put heat sinks on top of your avalons - it won't do anything good or bad, but will risk breaking the chips off of the board if the heat sink gets twisted or bumped or over tightened. SMC's are not the strongest type of chip package, and these babies are not really designed for top cooling. Chips you should cool with top heat sinks were designed for top heat sinks - and if you study the package form factors closely you will see clever reasons why they should be top or bottom cooled. (Like for top cooled chips, too many lead contacts on the bottom, or the chip fits in a socket which blocks downward thermal flow, or the wattage is just too high for through PCB cooling, blah blah etc..)
These asics want back side cooling, and we should rejoice because it's a reliable and easy (cheap) way to go. They have a metal pad on the bottom designed for heat flow into the PCB, with a kind of thick layer of plastic on top which does not really conduct heat that well.
And to all the liquid coolers and mineral oil guys - the wattage of these ASIC's is not super high so they don't make big heat like a hard core top end zillion core super clocked beast chip. So spend the money on fancy cooling systems if you want, but the only real benefit might be noise reduction. I don't think the ROI would be in your favor on technical merits, Burnin has demonstrated that he knows what he's doing. Now I love liquid cooling as much as the next guy and have a pretty sweet water chilled silent rig, but pragmatism is a virtue. ;-) Remember these ASICS are killer tech because they do more work for less power which means dramatically less total heat per square mm per hash (generally speaking) than an equivalent old school rig (cpu, gpu, fpga, whatever).
So keep cool when keeping it cool, peace out.
