DESIGN AUTOMATION FOR MULTICHIP MODULE — ISSUES AND STATUS

In this paper we will review the current state of commercial electronic design automation (EDA) tools for the design of multichip modules. MCM can be classified in terms of its substrate technology. The choice of substrate technology has important implications for the selection of design automation tools. A PCB EDA system seems more appropriate for MCMs with stacked via substrate which closely resembles the through-hole printed circuit board (PCB). A chip layout system may be more appropriate for MCMs with low-cost thin-film silicon substrate which typically uses staircase vias. The cofired ceramic substrate MCM which evolved from the hybrid integrated circuit technology may use the specialized hybrid EDA software packages available for the designing of hybrid integrated circuits. Historically, printed circuit board and integrated circuit design automation software evolved separately. There exists a boundary between the printed circuit board and integrated circuit design automation tools in the physical design hierarchy. This boundary can be an important limitation for the repartitioning of the physical design hierarchy within the MCM. We shall discuss in detail the impact of MCM on various aspects of EDA. In the area of physical design, we must face the traditional placement and routing problem for any high speed design. Problems such as system clock skew and tight timing requirements must be considered. As one push clock frequency higher, one also must consider discontinuities due to vias and bends besides the classical transmission line effect due to long wires. Other traditional physical design problems such as ground and power plane generation, physical design verification and mask tooling must be revisited in the context of various MCM substrate technologies. The thermal aspects of MCM design are strongly influenced by the placement of chips on the MCM substrate. Thermal design is especially important for high density MCMs using the flip-chip mounting technology. Here, the heat must be dissipated through the back of the substrate via thermal pillars or bumps. We still need to deal with the traditional coupled transmission line problems. Due to the small cross section, high performance MCM substrate interconnects are resistive and the transmission lines they form are lossy. Noise is another main problem for MCM design. For high speed MCM with many CMOS buffers, the ground bouncing noise resulting from simultaneous switching of a large number of CMOS drivers must be controlled through proper substrate and package design. We will conclude the paper by comparing existing VLSI and PCB EDA tools for MCM design.