Issue link: https://iconnect007.uberflip.com/i/1520701
MAY 2024 I DESIGN007 MAGAZINE 45 What measurements determine whether you can get away with using a traditional laminate for a high-speed board? Is it Df, Dk, or the need for low loss? Based on experience, observations, and many discussions with industry subject matter experts like John Johnson, director of busi- ness development at American Standard Circuits (ASC), the predominant determin- ing factor for design is frequency. Once it surpasses the 10 to 20 GHz threshold, there emerges a heightened requirement for transi- tioning to materials with lower losses, ideally 0.003 or below. With increasing frequency values, loss mitigation assumes greater sig- nificance. is is particularly evi- dent in frequen- cies exceeding 50 GHz, where attention shis towards the sur- face roughness of the foil employed and the fabrica- tion processes employed by board manufacturers to prepare copper signals. What are your thoughts on "hybrid stack- ups" with RF materials on the outer layers and FR-4 on inner layers? That sounds like it would be complex to fabricate, but is it the best of both worlds? You'd better know what you're doing, and you should be collaborating with your sup- plier from the earliest stages when attempt- ing hybrid stackup PCB designs. I've had the opportunity to design such hybrid PCBs, spe- cifically to address RF signal performance. But you can't focus solely on the signal per- formance of the PCB. You must account for the manufacturability of the PCB as well, due to the mismatch of materials being combined in hybrid PCB stackups. Ironically, hybrid stackups oen present as favorable solutions. However, material mismatches can arise as a potential challenge, and if not addressed and/ or accounted for up front, you are sure to have downstream issues. Integrating early-genera- tion pure PTFE materials with FR-4 materials, for instance, may pose difficulties in metalliz- ing plated holes, demanding meticulous atten- tion and precision to achieve optimal results. Nonetheless, there are a lot of excellent low Dk and Df materials currently available that har- monize effectively with FR-4, offering poten- tial cost reductions in the fabrication process. Is there anything else you'd like to add? Yes. I strongly reiterate that it's crucial to involve your PCB manufacturer at the earli- est stages of your design process. ey possess extensive experience work- ing with these materials on a daily basis. Understand- ing their capabilities is equally important, because certain PCB manufac- turers may lack the necessary exper- tise to successfully bring your project to fruition. erefore, a good, reliable, and proven manufacturing partner will offer valuable assistance not only in the initial stages, but throughout the entire design pro- cess, providing suggestions to improve design costs up front and optimize PCB performance and manufacturability. is collaborative and proactive approach will help you avoid costly delays and countless revisions throughout the design and manufacturing process. I'd like to thank you and I-Connect007 for allowing me this great interview opportunity. Lastly, I want to thank John Johnson of ASC for continuing to engage with me in many dis- cussions covering industry technology evo- lution, from material selections to UHDI, for today's complex PCB designs. Great speaking with you, Steph. ank you, Andy. DESIGN007 ...you should be collaborating with your supplier from the earliest stages when attempting hybrid stackup PCB designs.