kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Tue, Aug 20, 2013 at 08:03:54PM -0400, Chris Morgan wrote:
> one part footprint per-file, and use of the new s-expression format. I
> was wondering though why this format isn't the default yet? I have a
> June stable build.

AFAIK the code isn't ready, yet.

> So I was trying to figure out how we might name files that were stored
> in github. If we begin by assuming that pcbnew will use github
> directly, how should part footprints be named? Does the name inside of

If you were crazy an 'official' name is the IPC footprint name. Totally
unreadable of course! Search for 'IPC-7351B Naming Convention for
Standard SMT Land Patterns' (it's free), and be aware the revision C is
coming out.

> I'm trying to figure out how we can have kicad use the blob sha. Doing
> so would let us avoid issues where the filename was the same but the
> content differed.

Probably the whole footprint-table system will handle it :P
Also, consider that pcbnew copies the footprint (unlike eeschema), so
once it get inserted it is not 'vulnerable' to library changes.

As usual, library naming is more a personal/organizational issue (since
the standard is most unfriendly I refuse to use it). Actually often the
'built in' library is often designed with different technology
parameters so at the end I always had to redraw most of the component,
with any cad... Just pick a rule and do it consistently. I do it this
way and find it useful, YMMV...

- First of all each technology uses a different lib. So 0,2mm
  clearance parts have the save name as 0,1mm clearance one. but they
  live in another lib (another folder, actually). The fabrication level
  is part of the technology (there are exception, but these are
  product-specific...)

- Run-of-the-mill chip components are named a R, L, C followed by their
  EIA size. So R0603 is a 1.6mm resistor, then. This is because at least
  here in Italy the metric designation is not really used for these;
  also there is an ambiguity for a couple of sizes.

- Molded tantalum are CPxxxx-y where xxxx is the metric case and y is
  the Kemet package. Yes, Kemet, because we found that these are not
  always compatible between brand, since the pin lenght varies... anyway 
  CP7343-D is a typical example.

- Aluminum capacitors are CPCASE-y where y is the Panasonic case.
  Actually these *are* interchangeable, usually, so probably they could
  be named with their size, too.

- Most other components are named preferably from the JEDEC name, or the
  EIAJ name, or the manufacturer one, followed by the pin name pattern
  (or nothing if numeric). Alternative names are stored in the tags. By
  the way there are too many SOT23 variants around... example TO236 is
  a numbered SOT23, TO236-AnK is a single diode in SOT23. Of course
  MO220WGGD1 is not very readable as a name but at least is shorter
  than the IPC one.

  Example of manufacturer specific packages: NATIONAL-TJ7A is a D2PAK
  regulator (IIRC), LINEAR-MSOP12 is a non-standard MSOP12 used by some
  LT components.

- Other stuff is named with the name of the component/series. Example:
  WE-PD2-L is a Würth PD2 L-size inductor, which is *almost* the same as
  SDR0805 (which is a Bourns SDR0805 inductor). Almost because the PD2
  is bigger so even if the pads are the same, the courtyard is not!

- Parts with have an industry-standard size but no official size are
  named from the component used as a representative. Example:
  FINDER-40.52 is the typical 5-mm pitch, 2 form-C contacts relay.

- Really unique components use the component name. CB1aH-P is a huge
  relay with trifurcated pins (fun to desolder).

- Solder mask is the same as the pin; the fabricator does
  enlargement/ganging.

- I keep silk/assembly to the maximum material position and pre-trim
  silk against pad (since mask enlargement is done by the fabricator we
  can't use the builtin feature).

- Silk/refdes size are a big issue since they depend *a lot* on the
  fabricator. I use the 'standard' 1.2/0.12mm sizes but the old
  technology based on 0.2mm screen is still very common :(

Hope I have given some good ideas

-- 
Lorenzo Marcantonio
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