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OCTOBER 2021 I DESIGN007 MAGAZINE 83 line coupon with Polar Atlas soware driving an Anritsu VectorStar VNA), you can use the phase delay per unit length to get a very accu- rate measurement of transmission line effec- tive Er vs. frequency. In Figure 1, you can see that above 1 GHz or so, the variation is abso- lutely minimal. Higher-loss substrates will see more variation, but surprisingly less than you expect. Historically, with wider trace transmission lines, TDR measurement of impedance was a simple exercise of reading off the impedance from the TDR reflection, and the reflection over the whole coupon was flat. However, with fine lines, the traces exhibit an upward dri primarily from series resistance of the narrow trace. is upward dri must be removed by DC resistance compensation or launch point extrapolation before attempting correlation. Without correcting the Z O measurement for resistive effects, correlation will be poor, and if Er is used as a variable to correct the correla- tion then a false value for Er will be the result. Conclusion Whatever you are measuring or modelling it is important that you learn enough about the limits within the modelling tools' operation, and the physical limits of the "invisible" prop- erties of the materials in the sample under test. Without background knowledge and intuition based on the knowledge and the careful appli- cation of measurement and modelling it can be easy to be seduced into correcting the wrong variable. DESIGN007 Martyn Gaudion is managing director of Polar Instruments Ltd. To read past columns or contact Gaudion, click here. and related materials is a major and growing challenge. Not addressing thermal issues leads to thermal stress and early failure. As a designer, the typical challenges you face are: • Performance is driving the need for accuracy, and hence the demand, for 3D thermal modeling of the system including all the components—active, passive, and mechanical • Inability to accurately model the conduction, convection, and radiation of heat throughout the system • Simulating and analyzing the thermal behavior of the system, both transient and steady state is becoming impossible with the proven legacy solutions because they are unable to scale to absorb the growing density and complexity of today's system designs • The lack of accurate electrothermal co-simulation often leads to field failures • Extensive prototyping is a major drag on cost and time to market. To continue reading this column, click here. by Suketu Desai In recent years, driven by the demand for smarter electronics, device designers have witnessed enormous scaling of large and hyperscale integrated circuits (ICs) and embraced develop- ment directions toward high density and reliabil- ity. These devices have increasingly higher ther- mal performance requirements—both transient and steady-state—and meeting them is becoming increasingly complex and time consuming. Thermal Integrity and Challenges Today, ensuring thermal integrity of an electronic device is a multi-dimensional problem. It straddles both the active (transistors and ICs) and passive (resistors, capacitors, and inductors) components, as well as the associated mechanical connectors and thermal dissipation elements. With all these mounted on one or more PCBs, ensuring thermal integrity across this full spectrum of components COLUMN EXCERPT: All Systems Go! Comprehensive Thermal Analysis of a System Design

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