Handling high power in an RF/microwave printed-circuit board (PCB) requires not only effective circuit-design techniques, but PCB material capable of “getting the heat out.” High-power handling for a PCB material is synonymous with low loss and higher thermal conductivity. But in choosing a circuit material for high-power applications, such as power amplifiers and power combiners/dividers, many other PCB parameters come into play. This includes the maximum operating temperature (MOT) for a given material, which essentially describes a danger temperature above which performance and reliability problems can be aggravated.

Three approaches are commonly used for bonding multiple layers of PTFE-based circuit laminates, such as Rogers RT/duroid® 6000 series and RO3000®series materials. These three approaches rely on thermoplastic films, thermoset prepregs, and direct bonding methods, such as fusion bonding processes. The first two techniques require additional films or prepreg materials which function like glue to keep the multiple layers in one piece. The third approach employs heat and pressure to bond the multiple PTFE-based material layers into one piece.

Dielectric constant (Dk) is a key parameter to consider when choosing a microwave printed-circuit board (PCB). But what microwave circuit designers may not always appreciate is the “choice within a choice” with some PCB materials, or when it might make sense to select a circuit material with a higher Dk value. High-Dk circuit materials can make it possible to miniaturize high-frequency circuits beyond what is possible with lower-Dk circuit materials. Understanding where high-Dk circuit materials fit within an RF/microwave designer’s toolkit can provide engineers with a great deal of flexibility when developing both active and passive high-frequency circuits.

Dissipation factor, also known as loss tangent, is a printed-circuit-board (PCB) material parameter probably often overlooked when engineers size up their possible choices for PCB materials. But it is a parameter that can tell a great deal about how a material will perform in different applications and environments. And it is a PCB parameter that is certainly worth spending a little time to get to know better.

Achieving high reliability for a high-frequency circuit or system starts with the printed circuit board (PCB). The PCB material must deliver consistent performance over time and changing conditions, such as temperature. As explained in the previous Blog (part one of this two-part series), it is possible to spot PCB materials that are “built to last” by assessing a number of their key performance parameters, such as coefficient of thermal expansion (CTE). In fact, PCB materials such as Rogers RO4835™ laminates can be engineered for high reliability through a careful combination of material components resulting in specific performance characteristics.

High reliability is a goal and desire for all designers and end-users of high-frequency printed-circuit boards (PCBs). Since all of the components mounted on the PCB depend on it, it is expected to deliver dependable and consistent performance over time. But depending on the operating conditions, it can sometimes be difficult to achieve. In an attempt to help, the next two Blogs will explore PCB material reliability: this blog, Part 1, will review some of the general obstacles for a PCB material to achieve good long-term reliability while the next blog, Part 2, will take a close look at how the characteristics of one particular PCB material add up to good long-term reliability.

Millimeter-wave frequencies (about 30 to 300 GHz) were once associated with at least two things: circuits for these frequencies are extremely difficult to fabricate, and they will probably be used for some military-electronics application. Because these frequencies are available for use without licenses, a growing number of circuit designers are considering different applications at these higher frequencies and, of course, choosing the right printed-circuit-board (PCB) material is an important part of any practical efforts to realize millimeter-wave circuits. Here are some things to be aware of and tips on how to design for millimeter-wave circuits.

Transmission lines are akin to electronic roadways, routing signals along different paths of a printed-circuit board (PCB). At RF/microwave frequencies, circuit designers often create PCBs based on three popular planar transmission line approaches: microstrip, stripline, or coplanar waveguide (CPW). Each uses circuit-board materials in a different way, with different results in terms of insertion-loss performance. By getting a grasp on the insertion-loss mechanisms for these different transmission-line formats, circuit designers can better match the mechanical and electrical characteristics of their circuit substrates to their intended applications and transmission lines when choosing PCB materials.