As with previous designs, the core of the Cray-3 consisted of a number of modules, each containing several circuit boards packed with parts. In order to increase density, the individual GaAs chips were not packaged, and instead several were mounted directly with ultrasonic gold bonding to a board approximately square. The boards were then turned over and mated to a second board carrying the electrical wiring, with wires on this card running through holes to the "bottom" (opposite the chips) side of the chip carrier where they were bonded, hence sandwiching the chip between the two layers of board. These "submodules" were then stacked four-deep and, as in the Cray-2, wired to each other to make a 3D circuit.