Advanced MCM-D micro-processor module for ATM wide-area network switching systems

This paper describes an advanced MCM-D microprocessor module and its high-performance cooling technologies for an ATM-WAN (wide area network) switching system. The MCM-D is fabricated on 2 Si-substrates using the stacking RAM technique to reduce module size. The MCM has 4-layer Si substrates, a microprocessor LSI, 4 ASIC-LSIs, 12 high-speed SRAMs, an FPGA and bus-driver ICs. By using the stacking RAM technique, MCM-D size was reduced to 63 mm×85 mm. This is 14% of the assembly area (200 mm×200 mm) of a conventional circuit using conventional packaging technologies. The MCM-D was mounted on an ATM line interface circuit board, and realized 25 MHz microprocessor functions with high-speed (access time 25 ns) and large-capacity (4 MBytes) SRAM cache and ATM line interface circuit functions in an ATM-WAN switching system. The line interface circuit board-mounted MCM-D has a high-performance cooling architecture without fin structure. The MCM-D module is mounted on a sub-board and has thermal contact to the main board through a rubber spacer with low thermal resistance. By using this high-performance cooling architecture, the MCM-D microprocessor module and the ATM line interface circuit board operate under conventional forced air cooling conditions without a fin structure. This MCM technology and high-performance cooling technology can be applied to ATM-WAN switching systems and future B-ISDN ATM switching systems