On Working WITH Your Layout Engineer

Tuesday, October 8, 2019

Author: Donald Telian, SI Guys - Guest Blogger

I have a distant cousin who spent his career doing high-speed PCB layout. At a family gathering we were learning what each other did for a living, and when he learned I’m in Signal Integrity he looked at me warily. I was one of “those” guys. He then shared how we was going crazy routing, re-routing, and re-routing a high-speed PCB because an SI Engineer was giving him constraints that were impossible to meet. Lots of time wasted, and he was clearly upset. Then I learned this was a “normal” part of his job. What should have been a simple exchange of familial pleasantries went haywire. Viewed from his eyes, I had to agree that we SI Engineers have a way of complicating things and can be difficult to work with. I apologized. Even more, I told him that someday I was going to write an appeal to SI Engineers to do a better job of working *with* their layout engineers. That day has come.

If you are a Signal Integrity Engineer, we are about to venture into one of the critical “soft skills” you’ll need to succeed at your job. If you are a Layout Engineer, please forward this article to the SI Engineers you work with.

If there were ever two jobs at odds with each other, it is the Signal Integrity (SI) Engineer and the Layout Engineer. The two tasks have grown up together, yet exploited compute power in very different ways. In an odd quirk of history, around the time Layout systems became automated (remember hand-taping?) we also entered the “high-speed era”. Just when it seemed the layout task was going to simplify, a new type of “digital” signal arrived; one that was looking far more analog than digital. As signals increased to tens of MHz an engineering discipline called “Signal Integrity” emerged. While automated netlists, back-annotation, and such ensured “Connectivity Integrity”, the Layout task had to jump another hurdle. “High-speed” meant it wasn’t enough to confirm the connection was made, SI would require specific things about the way the connection was made. Things like lengths, impedances, couplings, along with a dizzying array of ideas and terminology foreign to mostly everyone at the time.


In the Beginning

…there was Layout. Layout was clearly the incumbent and SI the new kid on the block. While it’s hard to picture in 2020, there was a time when SI engineers struggled to find something to do – even to justify our existence. We marketed our “skills” to design teams, trying to invent language to explain why and how we could be helpful. One of my favorite pictures at the time was a couple SI Engineers (although, we weren’t called that yet) sitting on a street corner holding a cardboard sign “will do analog simulation for food”. Really.

During the transition to the high-speed era, I cut my SI teeth at Intel working on the PC. While I didn’t realize it at the time, one of the greatest boons in my career was getting paired up with a savvy and seasoned layout guy named Gary. Gary had grey hair, knew his craft well, knew how to be the incumbent, and had a way of looking at me when I wanted him to do something in layout that was edgy if not unreasonable. In time SI Engineers would gain the upper-hand – and perhaps even abuse it – yet in the beginning there wasn’t the slightest chance we’d get away with imposing anything on layout that couldn’t be justified. This was particularly true on the PC, where commoditization and cost defined everything we did. So the gifts I was given were two-fold:

A. I had to learn the complexities and intricacies of the layout task, and fit my SI ideas and constraints around that.

B. I had to justify layout complexities I wanted to impose with real data, accompanied by a clear and compelling explanation of why.

If you began working in SI after the year 2000, it’s possible you were not given those gifts. Instead, you simply became a gatekeeper tasked with defining a “good” or “bad” layout – even though you may have little layout experience. Whatever the case, I strongly recommend all SI Engineers learn how to do those two things (A and B, above); we might call them the “Golden Rules of SI’s Interaction with Layout”. Your Layout Engineer is your conduit into manufacturing the product, and as such is an invaluable asset to help you understand how your ideas fit in the real world. 


On Working With your Layout Engineer, 7 Axioms and Guidelines

I like Layout Engineers, and have found them to be a unique set of individuals. Overall, they are hard-working, practical, focused, experienced, humorous, good communicators, and masterful at negotiating. I like to think SI Engineers have these qualities too, but sometimes SI positions get filled with Engineers who have theoretical training yet lack pragmatism; in short, more hard skills than soft skills. To help bridge the gap between SI and Layout, here are 7 things you should find helpful when working with your Layout Engineer.


1. There is not one thing an SI Engineer can ask for that makes the layout task easier. Not one. Feel free to accuse me of hyperbole in the Comments section below, but it’s helpful if you face this truth sooner than later. SI and Layout are intrinsically in tension, so you need to figure out how to work together and focus on the one factor uniting you: a working product delivered on schedule.

2. Your Layout Engineer has already been over-constrained by SI Guidelines and Engineers before you even arrived. This puts your tasks more than just in tension; it puts you at a disadvantage before you say anything.

3. Layout Engineers want the design to work too, and generally care more about schedule than SI. Actually, Layout is accustomed to being asked to get the Project’s fabrication back on track after others were late on their tasks. So don’t be surprised if and when your layout engineer is focused on schedule and presses you for efficient, clear, and actionable interaction.

4. If you enjoy a challenge, on your next project measure your success by the layout engineer’s opinion of you when the project is done. I do this; it’s how I ensure I’m succeeding at the two skills listed in the previous section.

5. If Layout asks for guidance on a certain intricacy and you’re not sure of the answer, say “I don’t know”. These are powerful words. Then, when possible, go find the answer using simulation, published literature, measurement or all the above. Given technology’s rate of change, some questions don’t have answers and “I don’t know” can be the first step in getting one.

6. When there are multiple ways to get the job done, let Layout choose whatever is most convenient for them. When Layout and SI reach an impasse, defer to layout. If that thought unnerves you, offer more or better data to tip the scales to SI.

7. Layout needs SI to make clear statements and requests in plain English. Better yet, using Layout’s terminology. If you are sensing I’m suggesting you learn how to look at the project from layout’s perspective and understand what they’re up against including their tools, clearances, DRCs, tasks and schedules, you’re right.

These are some helpful ideas from my perspective as an SI Engineer, but here are some thoughts directly from the perspective of layout engineers. 


Thought from Layout Engineers

To help SI Engineers improve our interaction with layout, I interviewed experienced layout engineers who I have found to be masterful at both layout and managing interaction with SI. Combined, they represent well over 100 years of layout experience. We talked about the habits of good SI Engineers, and what SI could do to improve how we interact with layout. Here’s what they told me.

a. As PCBs get more complex, the design process becomes increasingly a negotiation. All perspectives need to explain what they need and why, and know how to work with other perspectives across design tasks. This applies not just to SI and Layout, but also to Mechanical, Power, and so on. Engineering is multi-disciplinary, and layout brings the perspective of what is reasonable and manufacture-able.

b. It’s important to get to know the person you’re working with, and how to interface with them. Some want and need more explanation; others readily accept what you say. Once the relationship is established and respected, communication and progress becomes simpler. One Layout Engineer suggested “Go to lunch with your layout guy to form a good working relationship. Most of the time lunch will crumble any unwanted wall. Start the conversation at the beginning of the project, and then everything will flow.” See Figure 1. A good working relationship can be more difficult to achieve with remote design teams and functions. If you are in that situation and get a chance to meet distant team members in person, do it. Another Layout Engineer stressed: “If you meet someone in person they are easier to work with.”


Lunch with a Layout Engineer.

Figure 1: Lunch with a Layout Engineer. Lany has 34 years of layout experience.

c. When asked to describe what a positive interaction with SI looks like, they replied “we need specific information about what needs to be done” and the best engineers to work with are “the ones who can explain why”. They said a single SI person is helpful because “I can go to 5 different SI engineers and get 5 different answers”, which is frustrating. In fact, it’s a normal experience for IC Guidelines, SI Engineer A and SI Engineer B to specify contradicting layout rules. Imagine using a model or simulator that gave you a different result every time you used it – wouldn’t that would be frustrating? So a single source to interact with is helpful. It’s also helpful when hardware engineering gets involved to understand the issues, mediate the negotiation, take responsibility and make decisions. 

d. Timely guidance is imperative. SI needs to understand that layout performs “hundreds of times” what seems to us a single constraint. Not only do constraints need to be practical and reasonable, but changing a constraint after layout has begun forces a significant amount of re-work. Again, layout expressed untimely and changing constraints as a “normal” problem. To mitigate this, “Placement Reviews” before routing starts can be helpful. But “getting SI to participate can be difficult”. Let’s change that. Design re-use is another way to ensure constraints are clear and on-time. In other words, if the interface has already been simulated, constrained, manufactured and tested to work well, do not be afraid to re-use the same constraints – even cut and paste the layout when possible. For a diagram showing concurrent design and implementation, see Figure 2. Note that SI’s “constraints” and Schematic’s “netlist” are both needed for routing to succeed.


Product Development Cycle. SI (red) is concurrentwith Schematic (green) and Layout (blue).

Figure 2: Product Development Cycle. SI (red) is concurrent with Schematic (green) and Layout (blue).

e. In general, layout’s interaction with SI has been positive and manageable. This was good to hear. Yet when asked if SI asks them to do things that are unreasonable if not impossible, they did not hesitate to answer “all the time”. As such, as already stated, these successful layout engineers have learned to be good negotiators, to explain trade-offs, and provide data on what doesn’t work and why. In some ways, that’s engineering’s normal give and take of negotiating dozens of conflicting variables and constraints. However layout’s experience differs substantially based on the attitude of the SI Engineer, and sadly some of us have not yet learned how to partner.

f. Layout provides valuable input to the design and engineering task. Perhaps you’ve noticed I have consistently used the term “Layout Engineer”? Interestingly, in speaking with these experienced layout engineers, the terminology they consistently use is “layout people”, “designers”, or “layout person”. Why is that? It may be the perception imparted by engineering degrees, which they told me many layout engineers do not possess. Instead many have learned their craft “on the job”, gaining practical skills and experience we might lack. In my dealings with layout I have found them well-skilled at “engineering” in every sense of the word – typically providing essential insight and information I need to succeed with my SI task. If you looked at their job title you would see “CAD Engineer” or “PCB Design Engineer”. Titles aside, at times we have under-valued layout. I believe SI Engineers would do well to esteem the skills of Layout Engineers and ensure we do not waste their time as we would not want them to waste ours.

Working on a Team

One way or another, design teams learn to work through the challenges. As one Layout Engineer said “The project doesn’t die, that’s not an option.” From the perspective of job satisfaction, how we cooperate and fit our tasks together makes all the difference. While “schedule” can seem like an arch-nemesis, one layout engineer pointed out that wasting time and cost affects “not the company’s money, but our money”.

Multi-disciplinary collaboration has yielded tremendous progress throughout our industry. I remember when ICs started to arrange their pinouts for PCB route-ability, and now that is commonplace. And how about PCI Express allowing you to connect p to n and n to p if that made layout easier and save vias? Furthermore, multi-lane serial links that de-skew at the PCS (Physical Coding Sublayer) level without requiring length-matching on the PCB was a giant step beyond DDRx matching requirements.

Indeed, every shipping product has found a way to reconcile all the disciplines required for its inception. We all do it every day. My purpose here is to help us, as SI Engineers, find practical ways to improve the way we fit into the larger project team – particularly focusing on our interaction with layout.

In Conclusion

A look at Signal Integrity, In Practice wouldn’t be complete without pausing to consider those we work with and influence the most: Layout Engineers. How can our crafts better complement each other? How can we enhance our cooperation to ensure everyone’s interests are addressed? As you endeavor to do your job well, you will ask yourself these questions again and again. Thankfully, there are answers. Someday if those answers are feeling elusive, my hope is that you can come back to this article for a few fresh ideas.

Donald Telian, SiGuys - Guest Blogger 10/8/2019

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