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Connect the Dots: The PCB Design Secret Sauce for RF Applications

Design and manufacture of PCBs for radio frequency (RF) technology is a unique animal. RF had been considered a niche, thought of only in terms of television broadcasts, commercial airline phones, and military radar systems. Now, light industrial and consumer applications ranging from remote meter reading to home security systems are just the tip of the RF iceberg.

More and more new applications are now relying on RF, meaning PCB designers increasingly need to become fluent in the use of high-speed low-loss PCB material used in the production of boards for RF applications. Sooner rather than later, you’ll probably find yourself designing a board manufactured with these less familiar materials, so it’s important to understand challenges and best practices associated with them.

Are the benefits to high-speed, low-loss PCB materials worth it for my design? Yes, these materials are what enable innovation and have been vital to the creation of 5G wireless networks, autonomous vehicle development, and the internet of things (IoT). RF boards are more expensive to prototype, but if you adhere to best practices for working with the materials and specifications required for RF applications, you’ll have more success and be more cost-effective in the long run.

High-Level RF PCB Design Practices
Best practices begin with focus on manufacturability. With RF boards, the materials chosen will impact every element of your design, from thickness to layout to surface mounts. This makes the decisions about materials critical for cost-effective prototype and manufacturing.

Designers accustomed to concentrating on circuit speed and density must adjust their thinking and focus on potential issues with frequency. RF boards should be made from materials that minimize energy loss and maintain dielectric (Dk) uniformity. To do both, designers have to choose among dozens of different controlled-Dk and low-loss materials. What you choose will depend on your outputs, budget, and design requirements.

And your design needs to be cost-effectively manufacturable by your chosen PCB fabricator. Collaborating with them from the outset about materials will help avoid production issues related to copper surfaces, materials varying by layer, blind and buried vias, and surface prep for solder mask. All these elements are interrelated, and decisions made in one area can ripple through your design.

For example, designers must consider how the fabricator’s copper treatments will impact RF performance. It’s also important to factor in via structure as it relates to copper surface thickness. Multilayer RF PCBs can have layers whose properties differ a great deal, so it is vital to work closely with your manufacturer to balance performance with manufacturability.

The real key to optimizing your RF PCB designs is to choose tools, processes, and a manufacturing partner that meet your unique needs. Treat your PCB fabricator as a member of your design team—prioritizing open and persistent collaboration with each.

Best Practices at Work
Trust is everything in these relationships. We have adhered to the open channels mantra working with RF solutions-provider Krytar over the years. Offering the highest standard of RF test and measurement services available to the broadband industry, Krytar supports development of all types of systems, including radar and satellite.

For Krytar’s microwave components and test systems to work as designed, the RF circuit function must be optimal. If the board specs deviate from the PCB design by even a tiny fraction of millimeter, it can compromise functionality. The higher the frequency, the smaller the wavelength—making it critical to maintain tolerances and stick to design specification. That’s no small feat, even in the best of circumstances.

As Krytar’s PCB manufacturing partner, we evaluate the customer’s design to ensure the manufactured RF circuit will function as intended and are not afraid to provide input on the design if we think we have a better idea about how to build a board that will do what it’s supposed to do. This commitment to each other is what ensures positive outcomes.

Focusing on Continuous Improvement
RF applications will keep growing in number and increasing in complexity. For designers and manufacturers alike, this requires continuous evaluation of capabilities and improvement of processes. As RF applications became a bigger part of our business, our focus on continuous improvement grew in importance.

Commitment to quality is just as important as the commitment to the customer relationship. How we deliver quality matters, and that is never truer than during collaboration with designers. Those interactions are where we constantly find new ways to improve both process and product in the RF arena.

Designers should expect their manufacturing partners to exceed their expectations and create value in every aspect of the production process by fostering communication and constantly evaluating customer needs. The production process is not unlike the symbiotic relationship between components on a board. Each element of production should be viewed by all parties as part of a larger ecosystem where individual processes are managed as part of the interrelated whole.

The margin for error in the RF arena is tiny. Even a pixel-width flat spot on an arc can become a false antenna and create bad behaviors. The designer and manufacturer working together—able to focus on granular detail without losing sight of the bigger picture—have the best outlook for producing a quality RF PCB cost-effectively.

This column originally appeared in the February 2022 issue of Design007 Magazine.