Re: gEDA-user: PCB package creation guidelines

[Karel Kulhavy <clock@xxxxxxxxxxxxx>]

On Tue, Nov 16, 2004 at 10:43:02PM -0500, Daniel Nilsson wrote:
> On Tue, Nov 16, 2004 at 05:14:01PM +0000, Karel Kulhavy wrote:
> > Hello
> > 
> > I suggest that some PCB package creation guidelines were created:
> 
> Karel,
> 
> I'm not sure I completely understand the rules you have outlined
> below, maybe you could elaborate a little ? Anyway, here are my comments:
> 
> > 1) The centroid of the package must be really the centroid
> 
> Why do you feel this is important ? This could be quite difficult to
> ensure in some cases I think.

How does the automated population process work then?

> > 2) The middle of the silkscreen outline outlines the biggest outline that
> >    can occur.

The part has some nominal size and some tolerance. size+tolerance is where
the outline should be placed. This ensures when you place 2 parts one next
to the other, they will fit on the PCB even in the worst case.

> 
> > 5) It's permitted to have a protrusion in the outline at pin 1, this protrusion
> >    doesn't count for an outline.
> 
> Can you provide an example ?

http://images.twibright.com/tns/15dd.html

> 
> > Could you comment on this? Would your guidelines be different?
> 
> In general, I think adding whatever rules of this kind should be done
> as library checks in PCB and not only as documentation. Documentation
> is obviously needed, but unless there is code that warns about any
> violations the end-user can't be sure that guidelines were met.

You can't have a code that parses drawings in PDF datasheets and checks
the dimensions.

Cl<