Multichip module packaging for cryogenic computers

A high-speed multichip module for cryogenic data processing systems has been developed using new packaging and cooling techniques. The cryogenic multichip module achieves a cycle time of 1.5 ns by using high-speed high-electron-mobility-transistor (HEMT) ICs, low-stress cryo-multichip module (MCM) packaging, and a stable cryocooling system. The HEMT multichip module consists of 20 3 K-gate HEMT ICs on a high-density, 115-mm/sup 2/ ceramic substrate. The chips are mounted by flip-chip bonding on a cryogenic ceramic multilayer substrate which has a thermal expansion coefficient similar to the HEMT GaAs material chip. The low-stress bonding material and cooling system are analyzed for reliability. Heat generated by the chip, which has a 12-W/cm/sup 2/ heat flux and totals 100 W per module, is removed by LN/sub 2/ (77 K) immersion boiling cooling. Dual refrigerators and a closed-loop system were used for reliability.<>