[cr0sh]

For something this large, it likely isn't "encapsulated" like a normal chip. I'd almost expect it to be left more or less "bare", mounted to some kind of very stiff PCB-like material (which is probably bonded to aluminum or something). Then wire bonds from the "chip" to the PCB.

The whole thing is probably then immersed into some kind of non-conducting fluid (mineral oil or fluorinert would be my two first guesses), probably vertically to take advantage of thermal circulation. Mechanical circulation of the coolant would likely be very gentle so-as not to disturb the wire bonds, unless they have something special to keep them in place (maybe the bonds and edge of the chip are encapsulated leaving the center bare?).

All of this is just guesses from somebody not an expert or even ever touched stuff like this, just based on what little I know about how normal sized chips are packaged.