In this paper we discuss how the problem of substrate-coupled switching noise (dI/dt and dV/dt noise) in mixed signal designs can be solved by using the substrate analysis capabilities in the SeismIC tool to drive the placement of macro cells using the Virtuoso Custom Placer (VCP) for Mixed Signal designs. An objective function consisting of area, wire length and other constraints such as substrate noise is minimized by VCP's annealing engine and the Constraint Manager.