vs3, can you tell us about the heat of the chips, without any dissipation layer, how much temperature rises?
I happened to make a big hole in the GND pad and once the bitfury soldier is padded on the backside with tin or thermal compound to insert a rear heatsink.
I had the sample boards that I made over the weekend run for a while without any heatsink on the back - just using the entire copper backside as a heatsink. They worked just fine at 50 bits speed (and I also let them run for a while at 51 and they worked fine too but I didn't let them run for long enough to be certain).
Also - keep in mind that the chips are not the only heat source. Chips produce about 80-85% of all the heat, but also the coil and regulator produce another 15-20% too. So heatsink on the back side helps them as well.
What we know for sure is that the bitfury chips can take a lot of beating - and I mean A LOT :
Chips have been tested to run at extreme temperatures. One user used a soldering iron to heat the chip to the point it desoldered. Hashing stopped only when chip started floating on solder and shortcircuited.
