Re: gEDA-user: Has anyone used SSOP28.fp?

[Steven Michalske <smichalske@xxxxxxxxx>]

On Jun 7, 2007, at 9:04 AM, Dave N6NZ wrote:

>
> L.J.H. Timmerman wrote:
>> Hi Dave and all,
>>
>> On Wed, 2007-06-06 at 11:24 -0700, Dave N6NZ wrote:
>>
>>> a) pcb paste layer gerber is directly from the pad layer, and I  
>>> think in
>>> many cases that lays down too much solder.  I haven't experimented
>>> enough to be able to say for sure.  I'd like to see some paste layer
>>> control added to the footprint definition.
>>>
>> Since this is on a per thickness, per material basis for the stencil
>> involved, I think this could be better handled in a specific  
>> "stencil"
>> exporter with a configurable positive(=larger) or negative(=smaller)
>> offset value for the pad-outline.
>
> That would be cool.  But I also think you want to be able so specify
> different shrinks on a per-footprint/pad basis.  For example, for  
> those
> packages with a big heat-sink pad, that pad may want a different  
> shrink
> from the rest of the pins on the package, and different from the
> default.  So, I could see some kind of format like:
>
> default -10% # any footprint, any pad
> sot223.2 -30% # sot223 footprint, pin #2 gets special treatment
>
> Maybe something like that should even go into the footprint  
> definition?
> (I'm thinking newlib here, I never use the M4 stuff.)
>
I agree that this would go in the foot print definitions.

This is something that needs a touch finer control.  some of the  
larger devices require a grid of solder paste on a pad.

This might be something to have a calculator on.  define a volume of  
paste per pad, and weather it is a grid.
this then gets scaled by paste mask thickness so that if i used a  
1/16th paste mask  i'd get small holes, and a 1mill would error out  
saying that the paste mask apertures were larger than the pad  
dimensions - x%

Steve

> But in the end, I think the pad size adjustment in pcb should apply to
> what is written to the paste layer gerber.  Converting to pad outline
> vectors is better done in the gerber previewer or some other gerber
> reader, since that yields a more general tool suite.  Of course, I  
> won't
> complain if pcb directly puts out the file that I need :)
>
>>
>>> b) My current method for prepping a file for the laser cutter is  
>>> a bit
>>> of a kludge.  Ideally, I'd like to see the gerber previewer have the
>>> option of exporting .dxf of the pad outlines from the paste layer.
>>>
>> If the exporter can be made configurable for not doing fill  
>> operations
>> on a pads in a pads-only-mode, then it's also possible to do this  
>> for a
>> DXF exporter.
>
> Yes, the fill just gets in the way as far as my laser cutting s/w is
> concerned.
>
> -dave
>
>
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