On 15 Dec 2011 at 16:16, Robert Kondner wrote:

>  I have found the paste aperture adjustment logic in PCB design
>  software rather poor. Such tools will under and over size well but
>  when it comes to QFN thermal processing or home plate designs for
>  passives these tools are totally lacking. I use PADs and Altium here.
> 
>  I would suggest folks generate 1:1  paste to pad apertures from the
>  CAD tools and then provide rules to the stencil processor. The rules
>  defined need to be coordinated with the stencil fabricator
>  capabilities and hopefully the data exchange can be done
>  electronically.
> 
>  I would be curious what PCB design tools you are using and how you
>  adjust paste aperture using that tool. I am sure there are new tricks
>  and capabilities I am not aware of.

I use Zuken Cadstar. I can (mis)configure everything to meet any 
design philosophy. I try to have all stuff well-defined "bottom-up" 
in the library and to avoid work-arounds in the designs.
In my own library (and some customer's libraries I'm responsible for) 
I use a separate stencil layer. Standard stuff all pads 1:1 on this 
layer, special stuff goes with well-defined under- or oversize 
(redefined in the padstack) pads on this layer, and if over/undersize 
or different pad geometries don't work, I set it to zero for stencil 
layer (padstack definition again) and "draw" figures (filled 
polygons) on this layer (not in the padstack definition but in the 
footprint library). Everthing fine and complete in the library.
Same procedure with oversize predefined in padstack for solder resist 
layer, Normally no need to touch anything later in the design.

Other approach is to use over/undersize during the postprocess (which 
I don't like for stencil neither solder resist layer, unless a 
customer or assembly house would ask me to do so).

Regards
Matthias Mansfeld

--
Matthias Mansfeld Elektronik
* Printed Circuit Board Design and Assembly
Neithardtstr. 3, D-85540 Haar, GERMANY
Phone: +49-89-4620 0937, Fax: +49-89-4620 0938
E-Mail: [log in to unmask]
Internet: http://www.mansfeld-elektronik.de


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