PCB Assembly Services - Screaming Circuits: Thanksgiving is over - How to prevent holiday induced design errors.


Thanksgiving is over - How to prevent holiday induced design errors.

Whether you ate turkey, ham or squash, the feast is over. If you’re like me, a big meal and a holiday weekend make it rather difficult to re engage your work brain come Monday morning.

Wait. Scratch that and reverse. If you’re like me, much to the chagrin of your (this year very small) family gathering, you were likely still attempting to solve problems in your head while consuming that traditional meal. But even with a brain that isn’t smart enough to ever really turn the computations off, there are plenty of opportunities for distraction and the accompanying potential for increased errors at quitting time the day before, or when back in the office (or at your home workstation crammed in next to the bathroom door) Monday.

Getoutitis1 is a risk to almost all of us when we have an non-work event or activity closing in. Human nature dictates that as the event gets closer, we rush to get out and open ourselves up to lapses in attention to detail.

What can you do to make sure you don’t forget to route the last few rats in the nest or change those two resistor values to mitigate some signal bounce? For me, once I get back to work after the holiday, the last day’s work always gets extra attention. The last hour even more so. If I made any design changes or component changes, no matter how small, I will re-step through my logic for making the change after I get back.

This goes double for the smallest changes - even a simple component package change. I once swapped an LED footprint on a PCB that had been successfully manufactured before. I rushed the footprint change about ten minutes before heading out the door to the airport. It was a simple change from an 0402 LED to an 0603. Everything fit. The traces were all symmetrical and on-center to both pads and I had plenty of space between the LED and the current limiting resistor.

Surprise, surprise, surprise! When I changed footprints, I triggered an update of all library footprints in the design. Unbeknownst to me, the footprint for the coin cell battery clip I had used had been altered between when I originally designed the PCB and when I made this tiny change. Updating the library brought that change onto my PCB and where I originally had a pair of CR2032 footprints, I now had a pair of CR1220 footprints. Card holder Bottom view w big battery on it

CR2032 to scale. The silk screen on the board is incorrect for the placed clip

I didn’t find this out until the manufacturing floor did one of their pre-build checks. Of course, I already had 600 blank PC boards, 1,200 CR2032 battery clips and 1,200 CR2032 coin cells on hand. Fortunately, the traces were still connected to the footprint pads, so all I needed was a new battery clip and the smaller CR1220 cells. If those traces hadn’t rubber banded to the smaller battery clip pads, I would have had to scrap all of the boards and I would have missed my deadline.

Always double check last minute work.

Duane Benson
1 Getoutitis /get·out·itis/ verb 1. The rapid reduction in ability to focus on fine on the task at hand due to an approaching significant event. 2. An increase in tension as time before a deadline runs out. 3. A small particle of dryer lint that gets stuck on the left edge of your nose.

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And this is why I rigidly enforce a one-library-per-design rule. Every new board gets its own library, with indiviudal parts copied from previous designs as needed. The library, schematic and PCB are archived together as a zip file on release, to keep all of the design source inputs together. Shared libraries have bitten me too many times in the past.

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