Admitting failure is not always easy. It happens and failure is usually followed by a scramble to right the wrong. The thing is that scrambling is often the root cause. Stakeholders may not be aware of the risks involved with 11th-hour revisions. As an example, editing a few voltage names in the schematic can have a devastating impact on the power distribution network on the actual board.
As you rip through the board to make the shorts and open circuits go away, it’s easy to miss a convoluted copper shape that branches into an area where it is no longer required. Without a new review/simulation by the Power Integrity team, there is a danger of leaving a stub behind. There is no open or short to trigger a Design Rule Check (DRC) violation. The copper just exists without a connection. The fix comes down to eye-ball time which is always in short supply.
“The only real mistake is the one from which we learn nothing.”
Will an extra polygon of copper be enough to scrap a PCB? The answer is more likely to be “Yes” on an analog circuit than on a digital circuit. Even little errors that can be easily reworked end up costing more than the planned manufacturing budget. This is one reason that Hardware is hard. We will make mistakes. “The only real mistake is the one from which we learn nothing.” - Henry Ford
The goal is to assemble the widgets with a minimum of human touch. Cutting a trace and adding a jumper-wire could be the difference between good and so-so margins. Note that “margins” is a euphemism for money. We all want a pocket full of margin.
Image Credit: Bureau of Labor Statistics - While there may be risk to manage, the dangers of this job are relatively low
Gradually Increasing Risk Over a Career Arc.
As you progress through a career in layout, the boards get more components, more layers, more rules and more risk. A footprint that is created with the exact attributes in the data sheet may not be manufacturable. Mainly, this has to do with hole-size tolerance. The inherited defects related to hole tolerance only surface once the drill chart is generated.
Footprint errors manifest in other ways as well. Silkscreen and soldermask are common sources of component trouble. In any of these cases, it is advisable to update the footprint in the library rather than making geometry and padstack changes in the PCB editor. A permanent fix may take an extra cycle but is better than a band-aid in the long run. Let’s start at the beginning.
Years 1-2 The Honeymoon
A junior PCB designer may not have the wherewithal to intercept issues like those mentioned above. They will often be given the smaller, simpler boards. Ideally, there will be more significant hand-holding. At this stage of her career, a pilot trainee will be able to take-off, navigate and land a plane.
They just don’t have the seat-time to fly an experimental prototype at this point. Likewise, the newer designer needs to lean on their copilot and ground-crew, that is - the engineers and vendors who can help keep the board on track.
Before long, the up-and-coming designer progresses to the more complex designs. This is probably the most hazardous step as we know just enough to be dangerous. Eventually, you find an equilibrium and you know that it’s time to move up to yet another level.
Developing library symbols
Simple 2 to 4-layer boards
Starting a network
Years 3-5 The Learning Curve
Board design is one of those occupations where a lateral move is also an upward move because of the exposure to more and different circuits. It may sound like denial but there is something about this quote from Thomas Edison: “I have not failed. I've just found 10,000 ways that won't work.”
Image Credit: History.com - Edison being Edison
Each additional component or layer adds to the risk that something will become a learning experience. Each additional engineer on the project increases the likelihood of getting conflicting/contradictory information.
Each of those engineers represents a function. Each new electrical function doesn’t just add to the number of coexistence problems, it squares the number of them. The more boards you do, the more likely you are to successfully deal with these challenges. There will be road-bumps also known as learning experiences along the way.
Defining PCB outlines and interconnect diagrams
HDI and mixed signal layouts
Expanding your network
Continued learning and certification
Years 6-10 The Maturation
As you go from early-career to mid-career, more responsibility finds your plate. By the time you get several years into the job, your opinion and expertise start to be put to better use. You’re able to look at a schematic and notice that the power-pin does not have a bypass cap associated with it.
You can spot a potential miswired net simply by pattern recognition. When you question these things and you’re found to be correct more often than not, you’re well on your way to pulling your weight. Never hesitate to ask when you see something unusual. It might be the “good catch” that saves the board from the scrap-heap.
Defining assembly subpanels and interconnect diagrams.
High pin-count SOCs including memory routing.
Contributing to your network.
Managing contractors and service bureaus.
Years 10 and Onward - The Learning Never Really Ends
Keep at it for long enough and you get to the Senior PCB Designer level. I’ve learned from lots and lots of mistakes! It’s humbling, even humiliating if you let your ego get in the way. Be like the duck with a calm exterior while furiously paddling below the water-line. It may not be easy but we find a way to make it seem so.
You may have heard that I just started a new job with the action camera maker, GoPro. Right before this, I was doing Class 3 boards bound for outer space applications. I can’t say what those boards do but I can say that field-service is not going to be a viable option.
The other thing about that business model is that the rocket doesn’t wait. The launch date depends on where the satellite has to go and your “bird” either on it or it’s not. Doing a board with thousands of components on a hard-stop deadline takes time management skills and a strong team-effort. By now, your leadership is important.
Coordinating overall design parameters and leading others.
Systems of multiple boards incorporating thousands of parts.
Setting an example for your network.
Advising management and others on the state of the art.
Some Mistakes are Going to Happen - Hopefully Only Once
After a while, there is almost no such thing as a small mistake. It doesn’t matter if it’s consumer goods for mass production or a precious few units that sell for big money, we’re compelled to execute as best we can. Small mistakes, in my definition, are contained in the drawings and don’t necessarily cause schedule-slip or scrapped boards.
For example, the drill file and the artwork match but the quantities in the drill table do not agree. There is no DRC flag to remind us to do the update to the drill chart. Instead, we tend to rely on a check-list to ensure that we get everything squared away before tape-out.
Image Credit: Author - One of my favorite mistakes, Go-Time comes and we’re adding stuff without removing “MADE IN THE USA” from the silkscreen.
If complacency sets in (see image) and we drift away from the guard-rails of following the check-list, it won’t be too long before a show-stopper comes along to remind us to take all of the little things more seriously again. No real harm this time thanks to the fab note instructing the vendor to remove ink from the bare metal.
When Things Go Wrong in Spite of the Process.
This advice came from a Mechanical Engineer and I’ll pass it on to you. “In the wake of a catastrophe, just keep your head down and keep working.” Success or failure, it’s always a team-effort. Avoid the finger-pointing even when the root-cause is clear. The team-player will focus on fixing the error(s) and preventing future occurrences.
Sometimes, as PCB designers, we’re making decisions on where to compromise between equally important factors. We get to the end and we learn what we can from any technical questions our vendor has with the data. You roll forward with everything you know.
One of my managers told me that “failing to plan is the same as planning to fail.” Have a plan. Make it a fool-proof plan and have a back-up plan anyway. A longer view of the horizon will help you clear those little bumps. One more quote before closing this story: (presumably from a test pilot) “Any landing you can walk away from is a good landing”. Our risks as PCB designers grow over time but, on balance, seem pretty manageable
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