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In this issue, we discuss some of the challenges, pitfalls and mitigations to consider when designing non-standard board geometries. We share strategies for designing odd-shaped PCBs, including manufacturing trade-offs and considerations required for different segments and perspectives.
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Estimated reading time: 6 minutes
By Tim Haag
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Tim’s Takeaways: Take It From Scotty, Simple Really is Better
I am, at heart, a die-hard “Star Trek” fan. When I was a kid, I was all about phasers, warp drive, and cool stuff like that. However, these days, I tend to put a higher value on production and storytelling. But like any fan (I’m avoiding “Trekkie” because, frankly, it’s kind of embarrassing), I have certain moments from the hundreds (if not thousands) of hours filmed for the various TV shows and movies that are among my favorites. One of those moments is in “Star Trek III, The Search for Spock,” when our heroes steal the Starship Enterprise from space dock.
The space dock scene is a pivotal moment in the movie. It is highlighted by excellent character interaction, humor, amazing music by the late great James Horner, and marvelous (for its time) special effects and cinematography. After some careful maneuvering to get the Enterprise out of space dock, Kirk and the crew fly away at warp speed, leaving their pursuers in the dust thanks to a little sabotage on the part of Scotty, the chief engineer. As it turns out, Scotty had previously removed some crucial components from the pursuing ship, causing their new and fancy computer to fail, and allowing the Enterprise to make a clean getaway. The scene ends with Scotty’s sarcastic comment about the overly complicated computer on the other ship, “The more they overthink the plumbing, the easier it is to stop up the drain.”
I’ve always liked Scotty more than anyone else on that show because, let’s face it, he was an engineer. But with this movie, I really came to appreciate his common sense and, if I’m being honest, the sarcasm he used to describe it. Even in a universe where transporter beams and deflector shields are as common as the Keurig on my kitchen counter, Scotty still knew when something was too complex to be practical. Wise words, and a lesson here for everyone.
In our industry, we design and manufacture amazingly complex electronics. I’ve laid out circuit boards for everything from large computer systems to small wearable devices, and even though they have had different degrees of design difficulty, they all had the same common objective: They all had to work correctly once they were built. To accomplish this, circuit boards are designed according to several standards to ensure they can be manufactured and work as intended. If you are in the design and layout part of this business, you are no doubt already familiar with many of these different standards. But once you go beyond the industry standards and into the realm of rules, processes, and procedures, the water can get murky.
Take, for instance, the rules and constraints we use in the CAD system to design the board. These are wonderful tools and an essential lifeline for both design and manufacturing, but they can work against you if you aren’t careful. Let’s look at a couple of ways this can happen:
- Too many rules: Our design databases can become afflicted with the same problem that Scotty alluded to, where overthinking the plumbing can stop up the drain. For example, instead of defining a unique rule for each net and thereby managing thousands of rules, group your nets together according to their needs and assign them all to a single net class. This will save you time and system resources.
- Lack of understanding: It is important to be very familiar with what your PCB design CAD system will do with the rules you feed it. I’ve seen some databases where rules have clashed with each other, like keep-out areas that block a copper pour that is supposed to connect to a specific net in that area. If you don’t rethink and redefine the rule, you have to either break it or turn checking off.
- Old data: Sometimes CAD databases get inundated with rules they simply don’t need. This can happen when people read in stock rules from their corporate library, fail to clean out older rules already in their databases, or both. I’ve opened up some designs that have rules not even intended for that design but reside in the database, taking up additional resources.
Mismanaged design rules can overload your system as well as generate unexpected results. I’ll summarize here by saying it is imperative that PCB designers know what rules are loaded into their systems and optimize those rules for the best performance of their design tools. But design rules are just part of the murky waters I described earlier. Now, let’s look at processes and procedures for a moment.
Processes and procedures are an essential part of any design department. They organize the workflow, ensure that the proper steps, checks, and balances are in place, and serve as a guide to the users in the department. However, processes and procedures are not ever-fresh on their own. They can get stale quickly and must be reviewed regularly to look for areas needing optimization and enhancement.
For example, do you remember many years ago when PCB designers had to create an aperture list with every set of Gerber files that was sent out? I remember how I used to manually optimize my traces and pad sizes to match the limited amount of aperture positions on the mechanical aperture wheel in the photoplotter. Thankfully, apertures began to be included in the Gerber file when the file format was updated to RS-274X, which certainly made life much more convenient for me as a designer. And yet, many design department processes and procedures continued to insist that a separate aperture file still had to be created along with the set of Gerbers. Why?
Look at the processes and procedures you have in place to determine whether you can increase your and your staff’s overall efficiency. Here are some areas to keep an eye out for:
- Design reviews: These meetings are essential, but do you need the same reviews you’ve always done? Many design reviews are driven by the needs and technologies of the time, so something may have changed and made some of these reviews redundant. On the other hand, some of your newer processes may reveal the need for an additional review at a spot you didn’t expect.
- Workflow: Just as with the aperture list, areas of your documented workflow may have changed. Over time, you and your staff probably have adjusted to these changes without realizing it, and you could be in for some surprises when you hire and train someone new.
- SOPs: Like the workflow documentation, CAD departments often have a bunch of SOPs to help with everything from how to create a padstack to filling out a timecard. While SOPs like this should be documented, more often than not they exist as hidden text files and sticky notes. Here is where open communication is essential to ensure that everyone in the department is aware of process changes and where to find official documentation on how to stay current with these changes.
To keep our department processes from getting “stopped up,” we must work diligently to prevent our workflows from being unnecessarily complex. As we have seen, this includes not only the processes and procedures that guide our groups in their daily work, but also the design rules and constraints used to lay out a circuit board. Until next time, keep on designing everyone—and yes, “live long and prosper.”
This column originally appeared in the November 2023 issue of Design007 Magazine.
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