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Subject: Re: [geda-user] pcb file format
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From: "John Griessen (john AT ecosensory DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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Date: Sat, 12 Nov 2016 12:24:04 -0600
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On 11/12/2016 11:00 AM, Charles Repetti (charlie94965 AT gmail DOT com) [via geda-user AT delorie DOT com] wrote:
> Pad [rX1 rY1 rX2 rY2 Thickness Clearance Mask "Name" "Number" SFlags]
>
> So the solder mask (paste) layer is defined per pad as "Mask", and for me has been the most important parameter to get right. The
> different manufacturers have different capabilities, and their DFM tools can be used to highlight this.


The guidelines for qfn packages say to use a wider solder-mask than copper for best soldering results,
and yet paste is usually an area less than pads to avoid shorts from squishing out as the part hits
during assembly, and to go along with the thickness of low cost stencils made of plastic, since they are
thicker than laser cut SS or electrodeposited nickel stencils.

Paste layer is generated and can be different than solder mask by a shrink or bloat amount.
That's what I was asking about.  It needs to be per pad, since a large center pad on a qfn package or
other land grid package might need different paste amount depending on vias or whether there
is a group of blobs of paste wanted.

There is no way with the current file format to allow arrayed blobs of paste except as
a double layer group where one large pad is flagged nopaste, and smaller arrayed pads that overlap it have paste.