On Thu, Mar 30, 2017 at 12:26 PM, Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com] <geda-use= r AT delorie DOT com> wrote:

> > > > >> John Luci= ani:
> > > > >> > I create stencil footprints with the same= basename as
> > > > >> > the component footprint and a ".sfp&= quot; extension. I have
> > > > >> > a script that parses the pcb and identifi= es all components
> > > > >> > that have a stencil footprint.
> > > >
> > > > I couldn't find this script on your page.=C2=A0 Cou= ld you please post or
> > link?
> > > >
> > >
> > > The script isn't quite ready for prime-time.
> >
> > But you tell why these scipts are good?
> >
> >
> The current script identifies the footprints that should be changed wh= en
> generating gerbers for a stencil. The completed script will perform th= e
> replacement.

To put it another way. Is it better to generate paste layer from a s= cript than manually editing each footprint?

I do not manually edit anything. If a part requires a stencil footprin= t it

is generated with a script along with the footprint.
=

For the other parts I do not bother. Future versions of the = script will accommodate parts
without sfp files by generating slightly r= educed stencil openings for each pad.

> > > > >> as thin line silk for checking or write the pa= ds to the sfp file.
> > > > >>
> > > > >> Do you have any specific file format for your = sfp files ?
> > > > >>
> > > > >
> > > > > I just make them as normal footprints. For example= - the stencil
> > > > footprint
> > > > > below is for a Cree XP-G LED --
> > > > >
> > > > > Element[0x0 "LED" "" "&qu= ot; 0 0 9996 2996 0 100 0x0]
> > > > > (
> > > > >=C2=A0 =C2=A0 Pad[-5511 -5511 -5511 5511 1968 2000 = 2968 "" "1" 0x0100]
> > > > >=C2=A0 =C2=A0 Pad[5511 -5511 5511 5511 1968 2000 29= 68 "" "2" 0x0100]
> > > > >=C2=A0 =C2=A0 Pad[-492 -3937 492 -3937 2952 2000 39= 52 "" "3" 0x0100]
> > > > >=C2=A0 =C2=A0 Pad[-492 0 492 0 2952 2000 3952 "= ;" "3" 0x0100]
> > > > >=C2=A0 =C2=A0 Pad[-492 3937 492 3937 2952 2000 3952= "" "3" 0x0100]
> > > > >=C2=A0 =C2=A0 ElementLine[7996 -2484 7996 -7996 100= 0]
> > > > >=C2=A0 =C2=A0 ElementLine[7996 -7996 -7996 -7996 10= 00]
> > > > >=C2=A0 =C2=A0 ElementLine[-7996 -7996 -7996 -2484 1= 000]
> > > > >=C2=A0 =C2=A0 ElementLine[7996 2484 7996 7996 1000]=
> > > > >=C2=A0 =C2=A0 ElementLine[7996 7996 -7996 7996 1000= ]
> > > > >=C2=A0 =C2=A0 ElementLine[-7996 7996 -7996 2484 100= 0]
> > > > >=C2=A0 =C2=A0 ElementArc[-7996 -10496 500 500 0 360= 1000]
> > > > > )
> >
> > The *.sfp files are used to define shapes for solder paste?
> >
>
> The shapes define openings in a stencil.

Then the shapes end up on the "stencil" layer, I think &qu= ot;paste" layer is a common name for this layer.

> > > For thermal pads I always use the grid. I have seen a lot of= production
> > > problems. Bridging and misalignments. On these large pads I = use a grid
> > > which reduces the coverage to between 50 - 60%.
> >
> > You use a grid because there will be production problems for a so= lid shape?
> >
>
> Yes. I have seen bridging and misalignments. All of the components tha= t
> I have used (with thermal pads) have recommended stencil openings
> as well as footprints. I either follow the datasheet recommendation or=
> the manufacturer application notes.

I do not perfectly understand this, do you have an example for examp= le datasheet or application note?

T= he datasheet for the Cree XPG is at

= www.cree.com/led-components/media/documents/XLampXPG-15B.pdf

Near the end of the file are the f= ootprint and stencil
recommendations. =

=C2=A0

Regards Nicklas Karlsson

http://www.wi= blocks.com =C2=A0