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From: "Britton Kerin (britton DOT kerin AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Date: Wed, 17 Aug 2022 08:37:28 -0700
Message-ID: <CAC4O8c-oHouf74A6oQMhLhdOB_xnAdsZ3E_UxK-wkknehi2qrA@mail.gmail.com>
Subject: Re: [geda-user] [OT] Solder paste woes
To: geda-user AT delorie DOT com
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Reply-To: geda-user AT delorie DOT com

On Wed, Aug 17, 2022 at 6:36 AM Erich Heinzle (a1039181 AT gmail DOT com)
[via geda-user AT delorie DOT com] <geda-user AT delorie DOT com> wrote:
>
> Two thoughts
>
> 1) I have heard of many people doing reflow at home who use locating pins on a precisely drilled support block that positively locates the pcb itself and the overlying stencil with matching holes when applying the paste
>
> 2) It could be that your apertures in the stencil are not optimal. Smaller apertures may allow more precise results. IIRC gEDA PCB solder mask aperture shrinkage relative to the pad shape can only be defined, if at all,  on a whole board basis.

You can set this per-footprint.  The paste blobs on the SMT part look
a tiny bit bigger than what I generally use, though it's difficult to
judge exactly.
The paste layer also looks somewhat thick.  How thick is your stencil?
 Also the paste does look a little thin.  I use a leaded paste for
prototypes (though I doubt that's the issue here).

> pcb-rnd treats each pad as a padstack,  where layer apertures on each layer can be defined individually,  or autogenerated, in the :padstackedit action.

pcb-rnd is not needed to control this.

I think the other reply is correct, and there is some stencil movement
at some stage in the process.  What I've always done is use scotch
tape to tape the board directly to the stencil on all four edges of
the board.  Once the paste is on I pinch the board and stencil
together and slit three pieces of the tape, leaving the fourth to act
as a hinge.  I then rotate the stencil and board apart using this
hinge.  I don't use any external framework.  I'm sort of surprised
this works but I've only once had a small bridge and not as bad as
what you're showing in dozens of SMT boards, and no other fab-related
failures ever.  I think rotating up is the key, as it doesn't seem
like it would be possible to reliably pick the entire stencil up
without introducing transverse movement.

btw pcbway is ~$450  even for smallish advanced process boards with
impedance control etc. and I've found them to be very helpful.

Britton