kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Mon, Jun 02, 2014 at 10:32:18AM -0400, Jean-Paul Louis wrote:
> Guys,
> 
> I am reading all this thread, and I am amazed that people suggest a silk shape that will HAVE TO BE REMOVED by the PCB fabricator.

The industry took a long time to discover this, too :D
And it isn't a full standard yet, too!

> This is adding cost to a PCB without any value added.

Without a separate fabrication layer I think could the best way to
achieve the assembly drawing. Otherwise silk+pads could be OK, too.
OTOH cost for silk is (usually) independant of how much ink you use...
I guess that for high volume production it would matter, but I have no
experience on that.

> The example shown by Lorenzo is a very good example. The yellow rectangle has zero value AND an extra cost, while just two lines (shown in white) provide the real value of locating the chip without hindering the manufacturing process.
> On top to it, because it is just inside the guard area (outside rectangle), it provide guidance for the 
> clearance between parts.

In fact the specs says that silk should be on the 'maximum material'
position. I don't remember if I drawn them that way. Anyway the idea is
that silk should be visible after assembly for inspection, this is the
*new* primary purpose of the silk. The *old* one, guidance for assembly,
is mostly obsolete (machines read fiducials, not silk screen)

Guidance for clearance would be actually done with the courtyard (dark
grey boxes). Rejected along the fabrication drawing, too... some CAD
system (the mentor ones, I guess, since they somewhat invented it)
actually do DRC on courtyard to avoid collision and such.

Sadly I have no money for PADS/Boardstation/Expedition whatever they
sell these days, so I don't know for sure (pcblibraries and the
footprint generator *are* by mentor, BTW)

-- 
Lorenzo Marcantonio
Logos Srl