A 640-Gb/s high-speed ATM switching system that is based on the technologies of advanced MCM-C, 0.25-mum CMOS, and optical wavelength-division-multiplexing (WDM) interconnection is fabricated for future broadband services. A 40-layer, 160 x 114 mm ceramic-MCM forms the basic ATM switch module with 80-Gb/s throughput. It consists of an 8 advanced 0.25-mum CMOS LSIs and 32 I/O bipolar LSIs. The MCM has a 7-layer high-speed signal line structure having 50-Omega strip lines, high-speed signal lines, and 33 power supply layers formed using 50-mum very thin ceramic layers to achieve high capacity. A uniquely structured closed-loop-type liquid cooling system for the MCM is used to cope with its high-power dissipation of 230 W. A three-stage ATM switch is made using optical WDM interconnection between the high-performance MCMs. For WDM interconnection, newly developed compact 10-Gb/s, 8-WDM optical transmitter and receiver modules are used. These modules are each only 80 x 120 x 20 mm and they dissipate 9.65 W and 22.5 W, respectively. They have special chassis for cooling. The chassis contains high-performance heat-conductive plates and micro-fans. An optical WDM router based on an arrayed waveguide router is used for mesh interconnection of boards. The optical WDM interconnect has 640-Gb/s throughput and easy, simple interconnection. The system, MCM, and optical WDM interconnection will be applied to future broadband backbone networks.