Microwave materials form the foundations for almost all high-frequency circuits and systems. Although they are often treated as commodity items, such as the FR-4 printed-circuit boards (PCBs) that are a "necessary evil" required for holding delicate metallized circuit traces and components, advances in microwave materials are as essential to the future of this industry as research and development in test equipment or semiconductor devices. In fact, without improved materials, there would be little improvement in semiconductors. As a way of paying tribute to the all-important suppliers of microwave materials, this issue features a special report on that very topic (p. 98).
The term "microwave materials," of course, is some what nebulous and can apply to a wide range of substances. Even in subcategories like PCBs, there are many types and formats, including those based on ceramic materials, on synthetic plastics such as polytetrafluoroethylene (PTFE), those that are laminated with conductive metal for forming circuits, and raw circuit boards awaiting metallized layers. Shielding materials also encompass a wide range of products. The cynical-at-heart circuit designer may see only the shortcomings in these various materials, such as the difficulty in matching the coefficient of thermal expansion (CTE) of a PCB with the metal circuit traces and components attached to it. In truth, however, all materials expand and contract with temperature. Experienced circuit designers learn to incorporate a material's behavioral characteristics into a final product design.
A jaded circuit designer may also feel that microwave-materials designers charge too much for their products, investing little in enhancements that would merit such prices. Having visited more than a handful of firms over the last few years, including WL Gore & Associates (www. gore.com) and Arlon (www.arlon-med.com), it is clear that these and other "top-shelf" microwave materials suppliers make major investments in research & development (R&D) on an ongoing basis. Sometimes these investments surface as a major new-product introduction. Frequently, the results of R&D investments are more subtle, materializing as performance improvements in existing product lines.
The special report on microwave materials provides an example of extensive research performed at Arlon in order to understand the thermal dissipation of the company's high-frequency PCB materials, in the hopes of improving microwave-circuit power-handling capability. That R&D helped to create a drastically improved version of FR-4 material that will benefit a wide range of RF/microwave circuit designers with improved structural and electrical stability at higher power levels. Perhaps such investments will help RF designers appreciate a bit more the value of microwave materials.