PCB Layout is Not a Job for Introverts

From the outside looking in, PCB layout looks like playing a video game. Maybe a boring video game when it comes to moving the silkscreen text away from pads and other exposed metal but a game nonetheless. That’s not entirely wrong. To differing degrees, I like doing placement, fan-out, routing and especially tuning a memory bus. Time flies while sitting there solving these puzzles. Even the tedium of generating drawings and data have their charms. 

That noted, there is much more than Tetris and Connect-the-Dots going on when you are responsible for fleshing out a schematic to create a virtual printed circuit board. This is a lesson I had to learn the hard way. While there is significant heads-down work, the collaboration must take place along the way.

The obvious input comes from mechanical and electrical engineers. The EE is with you almost every step of the way while the ME is there at the start and is looped back in before tape-out. Working shoulder-to-shoulder, or more likely, monitor to monitor with the author(s) of the schematic creates a bond between us.

My heroes burn the midnight oil to get all of their work done. Guiding the PCB design is one of their many tasks. I can forgive a sloppy last-minute addition to the schematic. By using pattern recognition, I might even be able to show them a potential error. “Where is the bypass cap?” “Why does this resistor only have one net?”

Understanding that the EE has a lot on their plate is one thing. Understanding that they, like me, have parts of their job that they really like and other parts that they do so that they can get back to the good stuff resonates. Of course, I like CAD. Maybe they don’t. They passed all of those winnowing Calculus and Chemistry courses because they are wired for that kind of thing.

Image Credit: One of our whitewater rafting guides - That was the entire Chrome OS Hardware team circa 2013. (Mr. shirtless is the other guide) I’m in the tank top showing off my farmer-tan!

In order to get a solid B average in college, I had to supplement Trigonometry with Poetry and History. I didn’t even realize that Pre-Calculus came before Trig. Those are high school courses but I skipped the Junior and Senior years so I missed out. Entering college at 17, I could choose whatever I wanted and it wasn’t math!

I went back on Qualcomm’s dime starting with Algebra. By the time I got to Calculus, I had to pair that up with Badminton. My father had health problems and after visiting him for a week, I couldn’t reboot. The point is that all of those engineers are really good at things with which I struggle.

Doing PCB layout requires a wide skill set. When it comes to design, there are three types of electrical engineers; those that think they can do it, those that know they can’t and the ever-so-rare one that really can. Beyond the CAD tools, there is the knowledge gained from experience with the fabrication and assembly houses and many others that I will outline below.

The IPC distills that information in their Certified Interconnect Designer program but that’s still just an overview. We continue to build on that knowledge by collaborating with the fab and assembly teams. Their capabilities may be current with the IPC standards or they might be well ahead. Our job is to steer the design towards the sweet spot on the cost/performance continuum.

That sweet spot will have a number of factors in play. First is the end-use market for the product. That is why we have class 1, 2 and 3 and why we may allow/require exceptions to those classes. In a perfect world, the fabrication notes would read as follows: “CLASS 2”. That covers just about everything except the color of the soldermask.

The reality, of course, is that the fab-drawing will specify materials tailored to the assembly process. We have to be tuned into the process in order to generate the correct exceptions to the standard. As an organization matures, they learn more and more about what can go wrong. This often leads to more and more standard notes on the fab drawing as they try to prevent recurrences of past issues.

Image Credit: Author - In the space of two years, the Chrome OS Hardware team had grown significantly - taking up the entirety of the Squaw Valley resort.

Have you ever heard of the Knoops scale of hardness? If you ever wanted hard or soft gold and wound up with medium, you might have had to resort to spelling out exactly what you wanted for the gold fingers or the wirebond pads. In this and other ways, the fabrication and assembly notes start to take up an entire page - especially in the more established hardware companies.

Aside from our favorite engineer and the reliable fabricator, the PCB designer is a hub around which many spokes radiate. Here is a list of folks who will take an interest as stakeholders.

• SI/PI: signal integrity and power integrity. I feel exposed without these people. If you’re interviewing and they ask if you have any questions, ask if they have SI and PI engineers on the team.
  
  Chances are those folks are too busy to be interviewing PCB designers. Simulating in software prior to committing to hardware is the mark of a company willing to invest in success. Without them, I’m inclined to over-constrain the board which is a cost driver and a time sink.

• Test Engineering: A test plan is essential to post-silicon verification and board bring-up. Placement and routing milestones should include their input so that the final product is ready to go on tape-out day.

• The Librarian: Be grateful if your company has one or a team of librarians to allow you to focus on the PCB layout. The board cannot be any better than the underlying footprints. Their job is low visibility until something goes wrong. Help them maintain their invisibility by suggesting improvements when called for. Do not be tempted to do those updates to a padstack at the board level because that will surely be lost the next time that device is used. If you are also the librarian, bear that in mind anyway.

• Various subject matter experts: Depending on what your company produces, there will be specialists who inform the final design. Much like the other engineers, they won’t be able to tell you exactly what they want until they see what you’ve done. You may not even know who these people are until the end. If that happens, it’s because you didn’t ask. Here’s a tip, ask.
  
  Once you know who the stakeholders are, you can include them in some of the preliminary discussions. The other option is to wait for them to come out of the woodwork after all of the docs are drawn up.

• Program Management: Someone has to keep the wheels turning in the right direction. If there is no program manager, chances are that at least some of that effort will wind up on your plate. Driving schedule is one of those thankless jobs that has to be done.

• Sales and Marketing: Beyond schmoozing customers, understanding what is required to be successful is of huge significance. The most successful companies have very visible and powerful marketing teams. A perfect board that didn’t hit the market window is not so perfect after all.

• Document Control: My first designer role was at a company that was run by two founders with the last names of Johnson and Wisherd. Coincidently, the two ladies who ran the document control room had the same last names. I learned early on that doc control seems like a clerk job but can be a power base.
  
  They don’t have to be the wives of the president and vice president to wield their power. All I can say is to humor them when they reject your ECO and want a more specific description in the title block. 

• Procurement: The buyers coordinate the entire bill of materials for cost and lead time. Getting all of the parts in-house on an on-going basis for all of the company’s projects is no small matter. Buying the right things at the right time for the right price is important and the PCB is one of the most important of those line items.

• Your boss: The boss answers to someone too. They can’t afford to be surprised but they can help you if they know you’re in over your head. Progress reports should be volunteered weekly if they are not already required. They have a distinct interest in you looking good because that’s how they look good.

Image Credit: Author - A wall of server boards to remind us to serve one another.

There are certain to be other entities that come into play depending on the specifics of the job. Coworkers, regulatory compliance, legal, HR, IT, and so on. Other than your manager, you don’t work for these people but if you want to be successful, you have to work WITH these people. Nobody does all of this alone.