Stephen H. Hall

Multigigahertz Causal Transmission Line Modeling Methodology Using a 3-D Hemispherical Surface Roughness Approach

As computer clock speeds continue to increase at a rate dictated by Moores Law, the system buses must also scale in proportion to the processor speed. As data rates increase beyond ~5 Gb/s, the historical methods used to model transmission lines start to break down and become inadequate for the proper prediction of signal integrity. Specifically, the traditional approximations made in transmission line models, while perfectly adequate for slower speeds, do not properly account for the extra losses caused by surface roughness and do not model the frequency dependence of the complex dielectric constant, producing incorrect loss and phase-delay responses, as well as noncausal waveforms in the time domain. This paper will discuss the problems associated with modeling transmission lines at high frequencies, and will provide a practical modeling methodology that accurately predicts responses for very high data rates.

A Practical Method for Modeling PCB Transmission Lines with Conductor Surface Roughness and Wideband Dielectric Properties

This paper discusses the modeling techniques to account for transmission line high frequency effects, and proposes a method to integrate these techniques into a practical and design-worthy model generation flow. The frequency tabulated transmission line models are capable of predicting wideband dielectric characteristics and high frequency conductor losses due to skin effect and surface roughness. They can be used to accurately model high volume, low cost printed circuit board traces which often have roughened trace surfaces and pronounced frequency variation in dielectric properties. The model accuracy is verified up to 20 GHz in frequency domain, thus suitable for multi-gigabit signaling analysis

Fundamentals of a 3-D “snowball” model for surface roughness power losses

SEM photographs of a typical copper conductors prepared by the PCB industry exhibit a 3-D snowball structure of copper surface distortions. We have developed an analytical basis for the electromagnetic scattering by the copper snowballs to predict additional power losses to those presented by the propagating medium that compare well with the observed measurements for a set of rough microstrip lines. In this paper we describe the fundamental concepts involved with the 3D scattering theory of our analysis.

Broadband Characterization of Complex Permittivity for Low-Loss Dielectrics: Circular PC Board Disk Approach

We present a nondestructive method for determination of the permittivity and loss tangent of low-loss dielectrics using printed circuit board (PCB) circular disks. Because it utilizes multiple resonances, this method is in high precision and broadband (500 MHz-12 GHz), covering the UHF, GSM 850/1800, 802.11b/g, WiMax, WLAN, and UWB bands. The method is simple and accurate based on closed-form analytic expressions of cylindrical symmetry, taking into account disk rim fringing fields and radiation loss. Numerical results are conducted for popular PCB material, FR4, and the self-consistent Kramers-Kronig (KK) relation is verified.

iNEMI HFR-Free Leadership Project report

Recent environmental concerns over the safety of the halogenated flame retardants (HFR) used in commonplace FR4 based printed circuit boards (PCB) has prompted market demand for HFR-free computer systems. Unfortunately, this transition has been made difficult by concerns of the Thermo-Mechanical and Electrical properties on the HFR-Free laminates. As an example, the critical electrical properties of most HFR-free dielectrics currently on the market make high-speed bus designs such as DDR3 problematic without increasing the cost of the system. The iNEMI HFR-Free Leadership Project was developed to address these industry concerns. This paper shows the project plan and status to date.

iNEMI HFR-free program report

The electronics industry is aggressively pursuing the removal of potentially toxic compounds from their products, including the halogenated flame retardants (HFRs) that were once widely used in electronics housings and cases and are still used extensively in printed circuit boards. Several leading electronics companies have publicly stated their intent to remove brominated and/or halogenated flame retardants from some or all of their products. The International Electronics Manufacturing Initiative (iNEMI), an industry-led consortium, is working with a number of its OEM and supply chain members to assess the feasibility of a broad conversion to HFR-free PCB materials. While IPC and JEDEC are developing halogen-free standard specifications and numerous companies have compliant materials, significant questions remain regarding overall readiness to make a transition to these materials. This paper will discuss results & conclusions from the completed iNEMI HFR-free PCB Materials Project, as well as outline current projects, which include the HFR-free High-Reliability PCB project, the HFR-free Signal Integrity Project and the HFR-free PCB Material Development Project.

Flexible printed circuit meshed ground plane modeling methodology

Flexible Printed Circuits (FPCs) are widely used inside electronic devices because they are easy to customize, enable relatively dense interconnect routing, and are the most physically flexible. Physical flexibility can be further enhanced by using a meshed ground/reference plane. Unfortunately, meshed ground planes can induce significant signal integrity problems that can roadblock high-speed channel design if not properly modeled. This introduces unique modeling challenges that commercially available software are ill equipped to solve. This paper presents a new simulation methodology to model FPC meshed ground planes in high-performance compute systems using existing quasi-TEM solvers with excellent measurement correlation.

Network Analysis for Digital Engineers

This chapter contains sections titled: High-Frequency Voltage and Current Waves Network Theory Properties of Physical S-Parameters References Problems