I recently wrote a bit about CAD library parts for QFNs and a reader posed an interesting question in response to it:

"Okay, that makes sense.. But why don't manufacturers of the part put out their footprints and schematic symbols for their parts in some common format?"

QFN Freescale eagle copper layer That is a very good question. When you purchase or download a CAD package, it will typically come equipped with an established library. Those libraries vary greatly in coverage and quality though, and, of course, they only cover the parts available at the time of release - and only a subset of the most popular, at that.

Who's job is it to make workable library components and or new ones? Ultimately, it usually falls to someone in the organization doing the circuit design. Some people will pay a third party to make the parts. NXP has made the complete library for their chips for the PCB123 CAD package. Some independent companies make it their business to create and maintain libraries. But, really - who should be responsible?

A components manufacturer needs to document a new chip anyway, but they'd have to make a library part for a dozen or so CAD packages for each part variation, depending on how much coverage they want. The CAD companies would need to create maybe a hundred thousand or a million library parts, depending on how much coverage they want, but the CAD package is useless without the library. The designer would need to create just the library components needed for the specific design, but that could easily double to design time. I guess that's why we have what we have - a combination of the above.

Still, the big question is: why isn't their a standard format for the libraries? That would make everyone's life easier. So, CAD folks; why no standard?

Duane Benson