Overconstrain? Underconstrain? Selecting Materials for High-speed Designs

Estimated reading time: 2 minutes

When selecting materials for a high-speed design, you need to be very familiar with the materials’ electrical characteristics, as well as the requirements of the PCB you’re designing. There are myriad details that need to be considered during the material selection process, and missing one iota can lead to your job being put on hold.

We asked Stephen Chavez, principal technical product marketing manager at Siemens, to share his thoughts on material selection for high-speed designs. Steph discusses material constraints, stackups, and the cut-off point when a “traditional” laminate will (and won’t) work for a high-speed board.

Andy Shaughnessy: What do designers need to keep in mind when selecting materials for a high-speed design?

Stephen Chavez: Regarding high-speed design, paying close attention to details is more critical than ever. This starts with dialing in and locking down a good foundation for the PCB, which is the stackup. The PCB stackup comprises the appropriate materials and structures to meet the design requirements and performance expectations. Locking in a good PCB stackup can be challenging, if not overwhelming when it comes to material selection.

Today, there exists a wide array of materials available for selection, encompassing diverse electrical, thermal, and other critical properties. Choosing the appropriate dielectric material hinges on the required frequency range and operational environment. As demands shift from conventional dielectric constants and thermal attributes (such as Tg and Td), there may be an associated increase in material costs as we move from standard materials to the more exotic materials. Materials boasting the lowest Dk and Df values tend to be pricier and may suffer from limited inventory availability, significantly impacting lead times. Where the Dk value is known as dielectric constant or relative permittivity, and the Df value is the dissipation factor or loss tangent, it tells a designer how lossy (electrical energy loss) a material may be. In simpler terms, it defines the ability of an insulator to store energy. It measures a material's ability to store electrical energy in an electric field. Additionally, when signal integrity and signal loss are critical, the micro-topography of copper foil cladding requires considerable attention. Numerous low-profile foils are available to mitigate and address signal loss.

To read this entire article, which appeared in the May 2024 Design007 Magazine, click here.