I’m one of the librarians, and Rene and I wrote most (all?) of the IPC-7351-compliant footprint generator scripts.
Also, I’m going from memory here…
There was an early IPC-7351C document floating around the internet which captured goals of the C revision. It was from one of the committee members and completely legit. However, in the many, many years that rev C was in committee (and unreleased) the industry began to heavily favor custom packages instead of continuing to use the existing packages for which IPC-7351 already gave fillet goals. This drove IPC to essentially decide that trying to keep a standard which can be used for designing footprints, when the packages that drove the footprints was getting exponentially harder, was intractable. So IPC, for lack of a better term (and being an outsider) gave up on IPC-7351C and later revisions.
There were two rev C things that were incorporated into the KiCad official library’s footprint generators:
- Rounded rectangle pads. These were known to be the best pad style long ago, but ECAD software didn’t support that pad shape. So the IPC-7351 series went from rectangle with sharp corners, to oval/oblong, to rounded rectangle in rev C. This was because the ECAD software had caught up and commonly supported this pad shape in the time frame when rev C was meant to be released.
- Silk indicators for pad 1. The early rev C document showed heavy use of silk removal for pad 1 indication. In my professional life, I had also come across this issue because packages were getting smaller, boards were getting more dense, and minimum silk line widths were dropping (at least, with the cheaper squeegy-style of printing). This meant that silk removal, rather than silk addition, was an easier way to capture pad 1 location on ‘modern’ boards.
The official footprint library follows those conventions above. While individual users are certainly free to have their own preferences, and the footprint generators are available for modification, Wayne has said that KiCad is targeted at ‘professional’ users and for that audience IPC is an industry standard that the industry can leverage. This means design engineers, technicians, manufacturing engineers, quality engineers, factory repair, field service, etc.
If the current footprint style doesn’t work for you, that’s OK, and the librarians are trying to make symbols and footprints for any and all KiCad users. Hopefully the library is high-quality and works for everyone. But sometimes it doesn’t. And the librarians are human and make mistakes too. I’m only trying to explain where this came from (since that’s missing above) and say that discussion is welcome. Though, I hope it’s quite understandable that in the end some decision has to be made and I believe strongly that the librarians always worked hard to make the best choices with the information available when a decision needed to be made. Hopefully that’s clear when looking at the library as a whole, taking into consideration that nothing is perfect.
Another thing is that the early rev C document I refer to was scrubbed from the internet when IPC decided not to pursue finishing and releasing rev C. So that further obscures finding the source material from which the library conventions were made.
And lastly, not all footprints were ported over to the new generators. And not all packages have an entry in IPC-7351. So for that reason, you will still see a mix of styles in the official footprint library.
I hope this helps in some way. I didn’t see any real explanation above and that is what I recall. Cheers!
this is why the “next gen” formats are soo important