Via-based Redistribution Layer Routing for InFO Packages with Irregular Pad Structures

Abstract

The integrated fan-out (InFO) wafer-level chip-scale package is introduced for modern system-in-package designs with larger I/O counts and higher interconnection density. A redistribution layer (RDL) in an InFO package is an extra metal layer for inter-chip connections. To achieve flexible and compact inter-chip connections, the RDL routing problem for InFO packages has become a crucial problem for modern electronic designs. In advanced high-density InFO packages, multiple RDLs with flexible vias are often adopted. On the other hand, to integrate chips of different technology nodes into one package, irregular pad structures need to be considered. To our best knowledge, however, there is no published work for RDL routing considering flexible vias or irregular pad structures. In this paper, we present the first work to handle the routing problem with pre-assigned pad pairs (i.e., the hardest pre-assignment routing problem) on the via-based multi-chip multi-layer InFO package with irregular pad structures. We first propose a layer assignment method based on a weighted maximum planar subset of chords algorithm to concurrently route as many inter-chip nets as possible. We then propose an octagonal tile model with a layout partitioning method to tackle increasingly popular irregular structures. Finally, we develop an efficient linear-programming-based layout optimization algorithm to find solutions with high-quality wirelength and via arrangements. Experimental results demonstrate the effectiveness and robustness of our algorithm.