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PCBs can be subjected to a variety of environmental conditions, which can cause changes in the material and alter how a PCB operates. For those who are less familiar with circuit material properties, there is often an unrealistic expectation that material shouldn’t change electrical performance when subjected to different environments. Actually, all circuit materials will change some properties when evaluated within a changing environment. Some properties may change more than others and some materials may have more change than others, but they all do change.
The materials formulated for use in high-frequency PCB applications are formulated so that critical electrical properties have minimal change when subjected to a changing environment. In the material development process, it is always a juggling act to allow some properties to change more so other properties will change less. All engineers typically struggle with difficult tradeoffs on just about any complex engineering task, and it is no different when formulating circuit materials.
One material property which is often overlooked until a field unit failure demands attention is TCDk (thermal coefficient of dielectric constant). This property is innate to all circuit materials; however, materials not formulated for high-frequency applications often have an extremely poor TCDk. Conversely, high-frequency laminates are formulated to have good TCDk properties and as a general statement, a good value would be 50 ppm/°C or less and this value would be an absolute value in the mathematical sense. Of course, the closer the material is to zero for TCDk the better.
Read the full column here.
Editor's Note: This column originally appeared in the August 2014 issue of The PCB Design Magazine.
Nolan Johnson, I-Connect007
Nolan Johnson checks in with Polar’s Martyn Gaudion on the evolving needs of global PCB manufacturing markets in a post-pandemic world, where generating accurate PCB specification documentation is essential to successfully navigating today's rampant supply chain constraints. Polar has positioned itself to meet these needs through agile software product developments that allow OEMs and fabricators to simulate material interactions and end-product specifications, including in-demand features like a comprehensive "structure view" that allows users to visualize all the transmission lines on a given a PCB. Though keeping pace with the demands of a rapidly growing industry has been challenging, Polar's commitment to innovation has kept its software suite ahead of the curve.
I-Connect007 Editorial Team
It makes a lot of sense: During times when the supply chain is stretched to the breaking point—and the last few years certainly qualify—what if PCB designers created boards that used fewer components and less laminate? Do PCBs still have to be 0.062" thick? Why not reduce layer count while they’re at it? Andy Shaughnessy and Nolan Johnson spoke with I-Connect007 columnist Dana Korf about the idea of designing a PCB with material conservation in mind. Is it a great new idea, or are we opening a whole new can of worms and a separate group of problems?
Didier Mauve and Robert Art, Ventec
As the second in this two-part series, The Printed Circuit Designer’s Guide to... Thermal Management with Insulated Metal Substrates, Volume 2, by Didier Mauve and Robert Art builds on the material presented in the first book by describing up-to-the-minute products and design techniques for thermal management with IMS.