If it was BGA I wouldn't be messing with it. The QFN is bad enough by itself. I wish this chip had a larger cross-section of pad at the edge, which would make checking solder jobs better because it'd wrap around a bit. I think the most problem I have right now is being able to stick the chips down reliably. The alignment is difficult because there's basically zero reference for when it's in place (and it has to be correct within a quarter millimeter on two axes) and I can't trust floatation because if there's enough solder on the belly pad to float into place the pins might not get soldered, and if I press it down to connect those the belly solder could bulge out and short across to anything, including the corner Vcore pads and short out basically anything.
I've succeeded in getting two of four sticks hashing unstably and unreliably but I have seen submitted shares. I can't say for sure what the issue is that gets the chip working haphazardly at about 10% capacity, because the breakout boards were pretty much all-or-nothing. Could be signal integrity issues, I really don't know but I hope that's not the case because if it's a result of PCB layout we got problems. The signal traces are between ground planes - at least they should be if the etch fab didn't get layers out of order.
Anyway, here's a sneak peek at the sticks.
Got ya a fully populated boar with heatsink temporarily attached. The final heatsinks will probably be that dimension but anodized green. Note that about 2/3 of the visible area is the bigass regulator, complete with external FETs and 360uF of output capacitance for handling about 20A of low-volt DC. The adjustment pot is in the bottom corner.
Here's some crap plugged into my jankety powered hub. The crapstack in the back you might recognize as a 1384 breakout board on the test regulator and running off one of Novak's USB adapters. The thing in the foreground is literally everything I just said except on one board quite a bit smaller. You might note a lot of flux crust and such around the ASIC. That's because I've pulled the thing, restuck the thing, wicked pads, pushed it around and whatever probably close to a dozen times. Ain't fun when every piece of the circuit seems to work just fine except for the core. Let's think of it as "in a vegetative state".