Design007 Magazine

Design007-Feb2021

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28 DESIGN007 MAGAZINE I FEBRUARY 2021 Feature Interview by the I-Connect007 Editorial Team e I-Connect007 Editorial Team recently spoke with PCB Libraries CEO Tom Haush- err, who has spent much of his professional life dialing in the processes related to footprints and CAD libraries. We asked him to run down some of the more common challenges that he sees, as well as some solutions and work- arounds. One point emerged several times during our chat: Don't trust datasheets. Andy Shaughnessy: Tom, our readers tell us in surveys that footprints are a huge problem for them, and a lot of it seems to come from bad CAD library management. What are some of the more common challenges you see with footprints? Tom Hausherr: e number one mistake today is the polarity marking on diodes, where the EE engineer puts Pin 1 on the cathode and puts Pin 2 on the anode. en the designer does the opposite. ey populate the boards and when they plug them in, something smokes or doesn't work properly. Barry Matties: at is a pretty common prob- lem that we hear about. Why isn't more care given to that if it's such a common problem, Tom? Hausherr: I try to label the pins of the diode C and A on both the schematic symbol and PCB footprint so that you cannot possibly get it wrong—C for cathode, A for anode. But then again, when you're dealing with LEDs, many manufacturers put the polarity on the anode side of the component package. Electrically, the anode is the positive pin, and the cathode is the negative pin. But the marking indicator is on the cathode for diodes. To eliminate error rate, double check all diode and LED connec- tions. Matties: Right. We hear the same, not just with the LEDs, but with connectors, too, being a big issue with pin orientation. Hausherr: A lot of the connector manufactur- ers do not provide any pin assignments on their datasheets. I run into this all the time. You should coordinate connector pin assign- ments with the EE engineer's schematic. Also, Footprint Design Techniques: Don't Trust Datasheets

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