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        Sat, 12 Nov 2016 11:39:28 -0800 (PST)
Subject: Re: [geda-user] pcb file format
To: geda-user AT delorie DOT com
References: <0d49697a-80c7-d588-859a-56bc542f7e5d AT ecosensory DOT com>
 <f54225e8-dfc4-e160-ef35-f332615eafb1 AT gmail DOT com>
 <e44ac11b-f069-3ae3-e489-8cbb89863e99 AT ecosensory DOT com>
From: "Charles Repetti (charlie94965 AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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Date: Sat, 12 Nov 2016 11:39:27 -0800
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Precedence: bulk

Got you, thanks for the clarification. Since I use a contract 
fab/assembly, I've never worked directly with a stencil for one of my 
designs, though I've seen them at trade shows.


On 11/12/16 10:24 AM, John Griessen (john AT ecosensory DOT com) [via 
geda-user AT delorie DOT com] wrote:
> 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.
>