Material Selection and RF Design

Estimated reading time: 1 minute

Innovation rarely sleeps in this industry, and the RF laminate segment offers a perfect example. RF materials have continued to evolve, providing PCB designers much more than an either/or choice. I asked materials expert Alun Morgan, technology ambassador for the Ventec International Group, to walk us through the available RF material sets and how smart material selection can ease the burden on RF designers and design engineers.

Andy Shaughnessy: Alun, just give us a quick refresher: How are RF materials different from traditional PCB laminates?

Alun Morgan: RF covers a broad range of frequencies, often defined as the spectrum from 3 KHz to 300 GHz. At the low end, traditional materials are fine; however, the influence of the material becomes much more critical as frequency increases.

Shaughnessy: How does RF differ from HSD (high-speed digital)?

Morgan: They are two different worlds, with very different design requirements. RF is primarily concerned with the propagation of analog waveforms, whereas HSD is primarily concerned with the transmission of binary digital bitstreams. Each has its particular benefits and drawbacks. The good news is that materials designed for high-speed digital applications are also generally suitable for high-frequency analog circuits.

Shaughnessy: What do PCB designers moving into the RF space need to understand about material selection?

Morgan: There are some very specific electrical properties that are important when selecting materials for RF or HSD applications. The first is the dielectric constant (Dk) of the material. The Dk is the ability of the substrate to store electric energy in an electrical field. It is a dimensionless property and is quoted as a value relative to a vacuum, which has a Dk of 1. Why does it matter? It matters because it determines transmission speed and must be accounted for when calculating the timing and synchronization of high-speed signals; it is also crucial for impedance matching and control. The Dk is very much a design consideration, and specific designs may require higher or lower values.

To read this entire article, which appeared in the April 2025 issue of Design007 Magazine, click here.