PERFORMANCE DRIVEN LAYOUT FOR THIN-FILM MULTICHIP MODULES

This paper addresses some of the problems encountered in propagating high speed signals on lossy transmission lines on the substrates of thin-film multichip modules. The interconnect lines on thin-film substrate are relatively lossy in the respect that the total resistance of such a line is typically comparable to its characteristic impedance. If such a line were terminated with a load resistor appropriately valued to minimize signal reflections and resonances, the voltage divider formed by the terminating resistance and line resistance causes undesirable attenuation of the output signals. In addition, each terminating resistor dissipates quiescent power on a high density substrate, generating a substantial amount of heat in a small area. Instead of being terminated by resistors, the distributed resistance of the lines are used to critically damp out the signal resonances. With the flexibility of the rubber-band routing and the efficiency of a dynamic data representation based on the constrained Delaunay triangulation, lossy and unterminated transmission lines can be generated to successfully propagate high speed signals. The SURF (Santa-Cruz ULSI Routing Framework) layout system is being developed specifically for thin-film MCM substrate design. The system is performance driven, featuring variable width, variable spacing, evenly distributed spacing, and thermal via insertion. A flexible topological routing model, called rubber-band sketch, together with a dynamic layer representation based on the constrained Delaunay triangulation, is used to control the reflected noise, coupled noise (crosstalk), simultaneous switching noise, and thermal resistance.