Issue link: https://iconnect007.uberflip.com/i/1520701
16 DESIGN007 MAGAZINE I MAY 2024 Shaughnessy: We are always saying that designers should talk to their fabricators, but then they don't. What would you ask your fabricator in this case? How would you approach that communication? Moyer: Yes, one of the big things to work on with your fabricator is when your loss require- ments are tighter than normal, affecting dielec- tric thicknesses, trace width variances, and so on. If you need to hold constraints tighter than the IPC standards or you need to hold ±5% on dielectric layer thickness, work with your fab- ricator. You must ask, "Can you do that?" As the designer, I want to go to a stairwell con- struction, which means our structure will be between my outer layer, and my reference plane is now prepreg, which has variants. e overall dielectric thickness is based on the fabri- cator's hydraulic press, venting patterns, and so on. Can my fab- ricator hold the tolerance I need or do I have to go to construction? Kelley: Don't just talk with the fabricators, but also with the base materials suppliers on those specific topics because, in some cases, you can choose one prepreg style over another and get a little bit better thickness control for your dielectric. So, it's worth having those conver- sations with the CCL supplier as well. Shaughnessy: Ed, you previously mentioned that the traditional CCL folks weren't really into the RF space because there is a lot of communication between the RF guys and RF designers. That's already there for them in the existing system. Kelley: Yes, absolutely. at's changing over time. ere are several examples of CCL sup- pliers that are trying to develop the expertise internally or find people they can bring on board who already have experience in those applications. It's getting better, but it's still a work in process. Historically, there is a long list of great products that weren't successful simply because there wasn't the technical or applications engineering support to educate customers on what the product can do. Shaughnessy: What else do the designers need to know in this area, Kris? Moyer: It makes sense to start looking at these "traditional" materials in place of the histori- cal RF materials. To summarize, designers need to understand both Dk and Df. Df is oen overlooked by many designers with no experi- ence in the RF realm. When you start getting these loss considerations and high fre- quency analog signals, designers need to be educated, so having those intelligent conver- sations with your fab- ricators and bringing in the laminate (CCL) supplier becomes more important. Kelley: I wanted to mention that you typically can get Dk and Df tables for each of the constructions of laminate and prepreg that a CCL supplier offers. It is important to note that from a user perspective, you need to be really careful about those tables because most of them are still designed for digital applications and may not fully account for conductor losses. So, before you really get going, the user and the supplier need to have that conversation about how those numbers were derived and if they're meaningful for the designer within the context they are working. Moyer: We talked about the surface rough- ness of the copper foil. You need to have those conversations with your fabricator and lami- nate supplier. is can factor in with a lot of the consumer-grade RF, Bluetooth, and such, which are technically in the RF spectrum, but where you are not in the X- or K-band, and so on. Don't just talk with the fabricators, but also with the base materials suppliers...