kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Tue, 6 Apr 2010, bennett78@xxxxxxxxx wrote:

>  
> A better candidate for footprints is IPC-7351
>  
> Here is a pointer to a viewer and spec:
> http://www.pcbmatrix.com/downloads/LPSoftware.asp
> I though there was a parser out there somewhere...

IIRC the format was closed since they actually make you pay for the
footprint generators for the various cad packages...

OTOH it's a CSV with an 'encoded' data field (like base64 but not
that) so if it isn't really encrypted we could extract the info playing
with the editor.

Just remember that these files only contains the PARAMETERS of
the pad (pitch, pin size and so on). The actual shape and position is
calculated using the technology parameters set and the formulas in the
IPC standard (you have to pay for these).

Last but not least, it can only represents 'regular' patterns, i.e.
you can't say "I want this single pad bigger because it's a thermal
sink"

So the IPC format can be tought as a *source* of modules (you can
actually generate more or less the hole JEDEC repertoire in full auto with
them...) but not as a storage format (it can't even handle custom
graphics, only bounding boxes an playgrounds)

> Interesting that 3 different quality footprint choices are provided...

These are different compromises between integration (board filling)
and mechanical properties (tombstoning risks and similar things).
In my experience each board assembler want its own pad layout:
I actually had to redo a board (tooling, photoplots and all the other
stuff) because the new assembly had a p'n'p which needed bigger
pads for the SOT-23.

That aside, the IPC patterns are a good starting point for a custom
production library (yes, I have different modules libraries
depending on the assembler AND on copper weight: 70um has different
solderability rules than 35um).

The worst was that time when they made me *move a connector*
because there was 'shadowing' during THT wave soldering (I just *love*
reflow compatible connectors:D)

--
Lorenzo Marcantonio
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