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Mail Archives: geda-user/2019/03/22/05:08:49

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Date: Fri, 22 Mar 2019 10:05:59 +0100
From: "Gabriel Paubert (paubert AT iram DOT es) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
To: "Richard Rasker (rasker AT linetec DOT nl) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Subject: Re: [geda-user] Modify SMD stencil aperture size to prevent short
circuits?
Message-ID: <20190322090559.op775lcm6jc5ksnd@lt-gp.iram.es>
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On Thu, Mar 21, 2019 at 12:01:44PM +0100, Richard Rasker (rasker AT linetec DOT nl) [via geda-user AT delorie DOT com] wrote:
> After some searching, I found that decreasing the size of the openings in
> the stencil and thus the amount of solder paste ending up on the PCB appears
> to be a common way to prevent shorts of this nature.

Indeed, that's one of the reason which pushed me to switch to pcb-rnd.

When I still used pcb, I wrote awk scripts that edited the pcb file and
produced a temporary one which was exclusively used to generate the solder
paste stencils.

However, the pads were still centered, for 0402 and especially 0201,
I've found that slightly off-centering the paste towards the outside
improves the result.

> 
> Can anyone confirm that this is indeed a good idea? It would probably mean
> that I'd need to make two copies of each layout: one with the desired PCB
> pad sizes, and one with reduced pad (and thus aperture) sizes for stencil
> production. And what reduction percentage would be recommended? At several
> dozen dollars plus at least a week delivery time per stencil, I don't want
> to mess around too much with trial-and-error.

For 0.5mm pitch (~0.3mm wide pads), I reduce the stencil aperture by
50µm. That's with 125µm thick steel stencils.


	Regards,
	Gabriel

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