More CAD Footprint Woes

At this point, I really shouldn’t call them “woes.” More like business as usual. I’m talking about the need to make custom footprints, or at leas modify footprints. Back in the old days, the only thing needed to make footprints was some copper pads, maybe plated through, maybe not. It was pretty rare to even need to make a custom footprint. Other than the occasional odd switch or relay, it was all done.

I really need to just get over it, though. On the one hand, it seems like nonproductive time; like I should be able to get right to schematicing and layouting. On the other hand, it’s so common, I just need to see it as no different than any other routing task.

Starting at the top of my BOM, I have:

  • An MCU in QFN format – I modified a symbol and added a custom paste layer to the copper land
  • Two SOIC Mosfet drivers – I modified the symbol on an existing footprint
  • Some Mosfets in a PowerQFN package – Made a complete custom footprint
  • A Mosfet in SOT-23 package – Woo hoo! I found a workable part in the library
  • Some Power Schottky diodes – Custom copper land

Custom footprints

I have another Schottky, some TVS diodes, LEDs and a bunch of passives that came straight out of the library. It’s certainly not everything that needs footprint work, but with so many variations of the more complex parts these days, it safe to assume that any SMT project will require a fair amount of library work. It’s just the way it is.

Duane Benson
It’s a pain but at least it’s not as bad as 11811 has it

4 thoughts on “More CAD Footprint Woes

  1. The old PCB Libraries /PCB Matrix LP Land Pattern Wizard, now a Mentor Graphics product, saved me lots of time with footprint generation. I had the Pulsonix version that was really just a PADS ascii output imported to Pulsonix so I got two CAD package outputs for the price of one really! It’ll be interesting to see how Tom’s new PCB Libraries project fares.

  2. Ah, the “good old days” of 2D. One problem that is neglected is the Z-axis of footprints. With packages such as CircuitWorks designed to convert IDF files between 2D layouts and 3D mechanical designs we are now having to consider the Z-axis and create otherwise identical footprints with new names. CircuitWorks uses a database with part number/footprint to translate to a specific 3D model part. To keep the 3D models to a minimum they are named the same as the footprint. For example, a tubular capacitor mounted on end can use the same 2D footprint regardless of height BUT the conversion to 3D requires us to change our ways of thinking in order to show the correct 3D model.

  3. The productivity lost by having each designer, or group of designers, reconstruct schematic symbols and PCB footprints must be tremendous.
    It seems to be too much to expect CAD package providers to have up-to-date libraries; and even those still end up needing tweaks to conform to company standards and preferences.
    Footprints end up being tweaked again to optimize for the particular design and process combinations.
    Having the IPC land-pattern calculator is a big help, but I find that I end up with a lot of “the same only different” footprint versions for the same part from 2 manufacturers due to differences in specified tolerances.
    There is a place to post and trade part CAD information using a vendor-neutral format; There’s still a translation and tweaking step which the user needs to do to actually use a part.

  4. I looked at WikiComponents a few months ago but it appears to be dead-in-the-water, and also “imperial” biased.

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