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where footprints come from (was Re: Re: Internal PCB Units?)


--- In kicad-devel@xxxxxxxxxxxxxxx, Werner Almesberger <werner@...> wrote:

> The scenario I was thinking of was that you're given a data sheet with
> a footprint drawing and then you recreate that footprint in your EDA
> system.

The combicon were done this way, using pad sizes according to the IPC calculator... the sheet only states the drill hole, pad size is a consequence: the rule of thumb is to make the pad 1,5-2.0 the size of the drill, taking care of annulus requirement and other process constraint: for example our 'standard' process has a drill position tolerance of 0,2mm, you can have 0,1mm but you have to pay... also you pay a lot more if you need holes less than 0,4mm but it all depends on you fab facility...

> > Shell scripts :D I've done the whole Phoenix Combicon series with these.
> Whee ! Shell math is for the very brave :) Bourne Shell or bash ?

Actually zsh because I was lazy and zsh has floating point (maybe recent bashes have, too). It could be done in a fully posix compliant manner with expr(1) and fixed point... (guess that? the usual quantum thing :D)

Anyway it's done like this (snippet):

for PIN in $(seq 2 $PINS); do
integer PINPOS=$((($PIN-1)*$PITCH))
cat <<EOF
Sh "$PIN" C $PADSIZE $PADSIZE 0 0 1800
Dr $DRILL 0 0
Ne 0 ""

> > Not sure about this but have you looked into gencam?
> No, but what I found looks interesting. Would you happen to have the
> URL of the specification ?

http://webstds.ipc.org/ then follow the menu... 

> Yup, excellent point. A parametric design helps a lot with such cases.

Too bad you have to pay to have the design rules for IPC patterns :(

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