Design Rules Recipe: Solvability, Manufacturability, and Performance


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One thing that we’ve noticed lately: Each designer seems to have his or her own way of using PCB design rules. There doesn’t seem to be much agreement about setting or using design rules.

So, in this true experts panel, Mike Creeden of San Diego PCB joined Freedom CAD’s Scott McCurdy, Jay Carbone, and Rich Kluever  to share their views on PCB design rules. This wide-ranging discussion with Andy Shaughnessy, Nolan Johnson, Barry Matties and Happy Holden covers everything from identifying the required constraints to setting electrical and manufacturing design rules and managing these often disparate requirements.  

Andy Shaughnessy: Welcome, gentlemen. The topic of design rules keeps popping up, and there’s not much agreement about best practices. Or is there? Mike, can you talk about how you go about setting up design rules?

Mike Creeden: Design rules help us utilize the strength of our CAD tool to make the circuit do what we want it to do, and that occurs in three areas. I always talk about what I call the “designer’s triangle,” which are three perspectives when we look at the layout.

The first perspective would be the layout solvability. You have to solve the layout, and your design rules enable you to do that. I’m able to pin-escape from fine-pitch parts, and at the same time, I want to balance that with DFX or DFM. Second, physically speaking, I must address the concerns for the manufacturing process and capabilities of my supply chain. I want to optimize them because the more robust I can make it, the higher producibility and reliability I would have long term and in a production volume. Third, the other perspective is performance. Performance is many things, including signal integrity, power delivery, thermal, etc., and all those things have to be met.

We don’t want to over-constrain anything. And you cannot do one or two of those perspectives I just mentioned and ignore the other one. When we apply our design rules, there might be an EE as well as a layout person—sometimes, that is the same person—and then there’s also design rules from the manufacturing supply chain. They may be different than the physical layout rules to pin escape. All design rules should be added as early on in the layout cycle as possible. Then, it’s correct by construction.

Shaughnessy: Scott, can you take us through your process?

Scott McCurdy: I approach the design industry coming from my background of running a PCB fabrication company, where half the things that came to us had to be put on hold because something was wrong in the design. Sometimes, there was just no adult supervision at the other end. At Freedom CAD, we are a PCB design service bureau and create hundreds of designs each year, so I’m also including Jay Carbone, one of our top designers who lives for this stuff and is one of our better “interactors” with engineers, in this conversation. We deal with a lot of different personalities and skill levels. I also brought Rich Kluever, who was at Solectron for many years at the CM level running Valor, identifying design problems at the factory that was going to have to assemble this stuff.  Rich has tried to bake into our process and people more of a manufacturing perspective because every one of our designs goes through Valor twice.

To read this entire interview, which appeared in the May 2019 issue of Design007 Magazine, click here.

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