A simulated differential TDR probed the differential pair. However, this field solver does not display or output the actual differential impedance it must be teased out from a simulation.Ī virtual prototype of a uniform differential pair transmission line was set up with parameterized geometry and material properties. In this study, Keysight’s Path Wave Advanced System Designer, ADS, which has an integrated 2D field solver, was used for the analysis of a virtual prototype. Only a 2D field solver can accurately calculate the differential impedance. The challenge for fine line analysis is that the aspect ratio of trace thickness to line width can exceed 1, which means approximations are not suitable for analysis. The goal in exploring design space is to find a combination of parameter values that optimizes some feature, while maintaining the target impedance.

Dielectric constant of the soldermask, Dk_sm.

Dielectric constant of the laminate, Dk.

The design space for a microstrip consists of the following geometry terms: In this initial study, a differential impedance of 100 ohms is the target, specifically for microstrip transmission lines. Methodology to Explore Fine Line Geometries But this new geometry realm introduces a set of design tradeoffs.

A special feature of these traces is that their aspect ratio (thickness/width) can exceed 1.

In this paper we extend the exploration of design space to ultra-fine line features. With the recent introduction of the Averatek Semi-Additive Process (A-SAP™) process, linewidths under 1 mil are possible using the same fabrication processing equipment as for traditional 4 mil wide lines. Our subsequent papers will apply this methodology to differential pairs with no return plane, to cross talk analysis, and to attenuation analysis. The same methodology can apply to stripline geometry as well. This paper focuses on a novel technique of optimizing the geometry and material properties to achieve a target impedance using ultra-fine line microstrip differential pairs as an example. 224 Gb/s Per Lane: Options and Challenges

Transmission line geometry