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

[Dave N6NZ <n6nz@xxxxxxxx>]

Steven Michalske wrote:
> 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
> 
>

Yes, that's a better model.  I can't say if that meets the needs of 
people going to high-volume assembly houses, but it certainly meets the 
needs of and goes beyond the kind of process controls I can get on my 
workbench with my squeegee and toaster oven.

-dave


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