Environmental Effects on High-frequency Material Properties


Reading time ( words)

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.

Share




Suggested Items

RF Antenna Design on the Bleeding Edge

07/13/2023 | Andy Shaughnessy, Design007 Magazine
At SMTA Atlanta Tech Expo and Forum, I met with PCB designer Albert Gaines, owner of HiGain Design Services. Albert has been working on some really interesting, fragmented aperture antenna designs, and some of this stuff is really pushing the limits. Albert and I discussed his work with RF, the differences between COTS and custom antennas, and his efforts to educate engineers about what they can and can’t do.

Reassessing Surface Finish Performance for Next-gen Technology, Part 1

06/26/2023 | Frank Xu, PhD and Martin Bunce of MacDermid Alpha, and John Coonrod of Rogers Corp.
Over the years, various surface finishes have been successfully utilized, namely organic solderability preservative (OSP), immersion silver (ImAg), immersion tin (ImSn), electroless nickel immersion gold (ENIG), and electroless nickel electroless palladium immersion gold (ENEPIG), as solderable finishes for PCB and package substrates. All these surface finishes have their pros and cons, with no single finish being suited to all applications. As system designers continue to respond to new performance demands, it can be noted that ENIG/ENEPIG finishes have endured as a leading choice in many advanced applications where reliability is prioritized over cost.

Slash Sheets: Don’t Fall Into the Trap

06/08/2023 | Geoffrey Hazelett, Technical Sales
Slash sheets can be confusing, and this is a big topic, so let’s start big and drill down from there. Here’s the big picture regarding slash sheet references: They were designed to provide handy groupings of PCB materials (laminates, polyimides, etc.) that go into a stackup. These groupings are designed around mechanical characteristics to provide insight for PCB fabricators to identify similar laminates with similar properties.



Copyright © 2023 I-Connect007 | IPC Publishing Group Inc. All rights reserved.