Robust layer assignment for via optimization in multi-layer global routing

Abstract

In this paper, we study a layer assignment problem which arises during multi-layer global routing. Our layer assignment problem takes the total wire overflow and the maximum wire overflow of a given 2D global routing solution to form the wire congestion constraints, and asks to find a 3D counterpart through layer assignment such that the total via overflow and the total via count of the 3D result are both as small as possible while the wire congestion constraints are satisfied. To solve this layer assignment problem, we present an algorithm which first determines a net order, then applies a dynamic programming technique to perform layer assignment in a net-by-net manner according to the net order, and finally refines the solution iteratively until convergence. Our algorithm is guaranteed to always generate a layer assignment solution satisfying the wire congestion constraints. We tested our layer assignment algorithm on the ISPD'07 and ISPD'08 benchmarks and the results are very encouraging.