I am not an engineer but that board design looks crazy to me. Why on earth would there be 26 chips on 1 side of the PCB and 3 on the other side.
That looks like it would be a disaster to cool and the traces look whacky with the square layout of the chips on the side with 26.
My personal guess, which can be confirmed or rejected from ukrcoin, but ...
The 26 chips are the 16nm hashing chips - they will be cooled from the topside with a single large heatsink as there are no different voltage levels there (like it is at bottom of the chips). The board is designed for 12V operation and the chips are in string, so 12V / 26 = 0.4615V per chip (or even lower as there is MOS transistor and current sense resistor to control the power with their own voltage drop). The problem I can see here is that this voltage may not be enough for 100GH per chip and 2 boards will have a hard time to deliver the advertised 5TH, which is 2.5TH per board or 96GH per chip. On my opinion (according to the DEMO videos from Bitfury) for that hashrate 0.477V are required or a higher clockrate per chip, but only the test will show if it is still stable then.
The 3 chips from the other side are just communication chips and they do not produce extensive heat, so no cooling is necessary for them.
What you can see on 'hashside' of the board are not traces, but the borders of the power pads (VCC) per chip, because they are chained and the (two lines of) white dots at the edges are vias to connect VCC of one chip to GND of the other.