Microvias effect on high‐frequency signal integrity

Abstract

Microvias or high density interconnects (HDI) printed circuits are now being designed in ever increasing quantities. HDI brings some interesting new solutions to age‐old signal integrity (SI) concerns, and concerns that will grow as rise‐times continue to drop.This article focuses on five major areas of SI concerns—(1) noise: (a) noise‐reflections, (b) noise‐crosstalk, (c) noise‐simultaneous switching; (2) electro‐magnetic interference (EMI); (3) interconnect delays.In each case, HDI offers improvements and alternatives—but it is not a panacea. A couple of “cautions” are listed that can be a major stumbling block to HDI implementation, fortunately, they are not SI based. Important to SI is the materials used in HDI. Although not the focus of this article, the materials selected, as well as the dimensional stack‐up and PCB design rules, will influence SI and electrical performance (impedance, crosstalk and signal conditioning). Miniaturization provided by HDI will be a major contributor to SI performance.Finally, the SI example is also a case study in cost reduction. The “before” and “after” conditions are reviewed to emphasize the cost reduction and “time‐to‐market” advantages of HDI technology.