[sdiy] SMT PCB design with KiCad: rounded rectangle pads, correct centroid and initial rotation

Robin Whittle rw at firstpr.com.au
Wed Jan 3 15:10:49 CET 2018


I just designed a PCB for the first time with KiCad (free, open-source,
schematic and PCB software):

   http://kicad-pcb.org/

which was also my first SMT design.  I did a lot of research into how to
do it, and I was able to make a board with rounded rectangle pads, with
dimensions specified according to the (soon to be finalised) IPC-7351C
standard.

The footprints have correct centroid locations and initial rotations,
again according to this standard - the "level 2" option, one of two,
though the term "level" seems to be a misnomer.  This means that the
.pos file KiCad generates should be easy for a PCB assembler to use,
since they should not need to manually tweak anything in order to get
their pick and place machines, and the software which drives them, to do
the right thing with the components as they are supplied on tape.
However, I have not tested this yet.

I used the free version of Library Expert from:

  http://pcblibraries.com

to generate the footprints.  This is quite fiddly, since numeric values
need to be entered each time for each footprint.  The paid-for version
avoids this and is much more suitable for anyone doing more than a dozen
or two footprints.

Library Expert can export its footprints to KiCad format, and I did some
manual changes before importing them into KiCad.  These changes enable
me to make a printed sheet, via an SVG file, generated from the
ECO1.User layer, which carries simple outlines of all SMT components,
together with their value.  There is already another layer for this
which uses the references.

There's often no room for both references and values on the same image,
and I want a drawing with sets of values for manual assembly, and as a
guide for the PCB assembly company.  KiCad doesn't normally do this.  It
wasn't my idea - two experienced KiCad users have been doing this for
some time.

I documented my procedures at:

   http://www.firstpr.com.au/kicad/kicad-design-for-manufacture/

and opened a discussion thread about it at:


https://forum.kicad.info/t/footprints-with-rounded-rectangle-pads-correct-initial-rotation-generated-from-library-expert/9108


  - Robin




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