A Three-Layer Gridless Channel Router with Compaction

This paper presents a channel router that is designed to handle channels having irregularly-spaced terminals on different layers. The development of this router has investigated combining several basic wiring functions in distinct stages to achieve the required performance. Both grid-based and river routing techniques are used to provide a preliminary wiring of the channel. Subsequent routing phases employ via reduction and vertical compaction to improve the channel wiring. Layer changes in wires that are introduced during the via reduction stage tend to enhance the results achieved during the compaction process. The router resulting from this approach acts as a gridless router capable of handling three layers of interconnect. Details of the approach and the results obtained are discussed. The adaptation of the router to variable-width wiring is also discussed and illustrated.