Pad assignment for die-stacking System-in-Package design

Wire bonding is the most popular method to connect signals between dies in System-in-Package (SiP) design nowadays. Pad assignment, which assigns inter-die signals to die pads so as to facilitate wire bonding, is an important physical design problem for SiP design because the quality of a pad assignment solution affects both the cost and performance of a SiP design. In this paper, we study a pad assignment problem, which prohibits the generation of illegal crossings and aims to minimize the total signal wirelength, for die-stacking SiP design. We first consider a variety of special cases and present a minimum-cost maximum-flow based approach to optimally solve them in polynomial time. We then describe an approach, which uses a modified left edge algorithm and an integer linear programming technique, to solve the general case. Encouraging experimental results are shown to support our approaches.