This is a topic I have written about a few times, most recently in my August 2017 column, and with good reason. The answer, “it depends,” typically annoys engineers; fortunately, there is a list of items that can help the PCB designer answer the question of when to transition from FR-4 to high-frequency materials.
The bottom line is that FR-4 materials have been around a long time, and they work well within the range they are formulated to work. The same can be said for high-frequency circuit materials, which are also thought of as low-loss materials. However, there is a definite gray area that can muddy the waters when a designer is weighing a possible decision to switch from FR-4 to low-loss materials. High-frequency materials also have inherent properties that can benefit some applications that are not related to high frequencies or low loss. The material property differences between FR-4 and high-frequency materials are critical for the designer to understand when considering the use of either material.
It may be a good idea to compare properties of FR-4 to a commonly used high-frequency material. The low-loss material to be considered here is the RO4835 laminate. The FR-4 material that will be examined is a higher-quality, high-Tg FR-4 material. This comparison is mostly meant to trigger a designer’s thought process; there are admittedly exceptions with these materials and the properties mentioned.
To read this entire column, which appeared in the August 2018 issue of Design007 Magazine, click here.