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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.
Happy Holden, I-Connect007
I am always surprised when a colleague produces a statement about PCB laminates that seems incorrect or out of date. This need not happen today as the specialists at Isola have written an excellent book about high performance materials, now available for download from I-Connect007. Author Michael Gay, a 25-year veteran of laminate manufacturing, meticulously guides readers through the most pertinent questions regarding rigid laminates. This is essential information for everyone, including the experts, because the materials and applications for laminates in printed circuits are constantly changing.
I-Connect007 Editorial Team
In "The Printed Circuit Designer’s Guide to... High Performance Materials," the latest release from I-007eBooks, readers will learn how to overcome challenges associated with choosing the right material for their specific application. Author Michael Gay of Isola provides a clearer picture of what to know when determining which material is the most desirable for which products. PCB materials and DFM expert Mark Thompson says, “I love this book, particularly the sections on the effects of the glass weave, the history of laminate, and the difference between Dk and effective Dk."
I-Connect007 Editorial Team
Any discussion about high-speed PCB design techniques would be incomplete without considering the properties and requirements of the materials. Your material selection drives much of your design strategy when you’re operating at 28 gigabits per second or faster.
We recently spoke with high-speed design expert Lee Ritchey of Speeding Edge, and electronic materials veteran Tarun Amla of Avishtech and Thintronics, about the relationship between advanced PCB materials and high-speed design techniques. They discuss the challenges facing designers and engineers working with materials at speeds that were considered unreachable not long ago, and what designers need to know about material selection as board speeds continue rising toward the stratosphere.