Issue link: https://iconnect007.uberflip.com/i/1520701
MAY 2024 I DESIGN007 MAGAZINE 23 at's a good point. But I know of a military OEM that moved away from a PTFE-based RF-designed laminate material. One of their first steps was to get one of the conventional CCL guys to provide an ultra-low-loss material. ey switched to the new material. It wasn't seamless at first. ey jumped to a higher Dk and Df product and inched their way back with a better high-speed digital material. But they worked with the supplier and eventu- ally got what they needed and made the switch. e point being, it was a military OEM who was willing to look at something different than what they'd always been using. Shaughnessy: A lot of designers now get away with just using RF on the outer layers and then having whatever is needed on the internal layers, and it works. at's actually pretty common. In my previous company, one of our FR-4 products was used all the time with an RF supplier's laminate on the outside and the less expensive FR-4 mate- rial everywhere else. In the end, they're build- ing RF and digital into the same PCB. LaRont: As you mentioned, beyond Dk is also important. at's correct. With high-speed digital, you're talking insertion loss, but it's a similar concept. at is where you can maybe use the combi- nation of a dielectric that might not have been quite as good as the RF product, but with a smoother copper. e copper roughness really drives up losses at higher frequencies. ere's so much more that can be done with these materials, and it's a matter of getting the designer the information they need to be com- fortable designing with them. Shaughnessy: Where is this sort of informa- tion found? Is it in application engineering notes that come with the material, the drawings, fab notes, or all of them? I think it varies by the CCL supplier. Some are better than others at putting that information together. You'll see most of the CCL guys today will have tables of Dk and Df by frequency range for different constructions and prepreg offerings, which is very useful for the high- speed digital world. For the RF designer, I think you need to go above and beyond that. You need to have conversations with the RF designer like, "What informa- tion would help you be more comfortable designing with these products?" Most traditional CCL suppliers would improve by getting that infor- mation together and providing it to the design community, in particular. Also, the Dk and Df information that a con- ventional CCL supplier provides is typically measured by certain test methods, and those aren't always the same methods you want to use for RF. In high-speed digital product, the orientation of electric fields can be different than in RF. Shaughnessy: It's interesting that it matters the way you measure Dk and Df, and how your materials are oriented in the RF design. e direction of the electric fields really dic- tates what type of test method you want to use to provide the Dk and Df data. e CCL sup- pliers have learned a lot in that regard but are probably still gathering and publishing some of that data. Shaughnessy: Is the line being blurred between high-frequency/RF and the more traditional materials? Yes and no, but it's not simple or straightfor- ward. Many materials designed for high-speed digital applications can achieve the high-fre- quency/RF performance requirements, but There's so much more that can be done with these materials...