On 5/11/06, Olin Lathrop <olin_piclist@embedinc.com> wrote:
> Wouter van Ooijen wrote:
> > No, i have never dealt with a PCB of that complexity, but I answered
> > someone who was alarmed at the idea of a PCB without part numbers. If
> > finding the part numbers on a multi-color (probably magnified) printout
> > is difficult I don't think part numbers on the silkscreen will make
> > things easier!
>
> I think component designators (part numbers actually means something else)
> are a good idea on the silkscreen where possible.  They make debugging
> easier and make it just a little less likely that someone will screw up
> during manufacturing.  They may be technically redundant, but redundancy can
> be a good thing when trying to reduce human error.
>
> Unfortunately with the newer smaller components and more tightly packed
> boards, it's not always possible to put all component designators on the
> silkscreen.  I have developed several ways to deal with this using Eagle.
>
> I have gone back to all my library parts and added component designators in
> a small font in the tDocu layer, then also put component designators
> intended for the silkscreen in the tNames layer.  The smallest I use for
> silkscreen is size .05 with ratio 16, which comes out to .008 line width.
> That's the smallest I trust silkscreen to reproduce without explicit specs
> to the contrary.
>
> This scheme works with my GRID_BRD ULP.  This automates the creation of gray
> scale drawings of the top and bottom sides of the board.  The appropriate
> Docu layers are shown in full black to stand out easily, with the
> silkscreen, copper, and other layers in various shades of gray to provide a
> good visual match between the drawing and the board.  GRID_BRD also draws a
> 1" grid in light gray with labeled coordinates so that it is easy to find a
> particular X,Y coordinate on the board.  Then my INDEX ULP creates a part
> finder index that gives schematic page, coordinate within page, and board
> X,Y coordinate for each part.
>
> The assembly house gets the BOM, the board drawings, and the part locator
> index.  I've had assemblers comment to me that they really liked the parts
> locator and wished everybody else would provide one too.
>
> I put an example board drawing at http://www.embedinc.com/temp/eusb2_top.gif
> and the corresponding locator index at
> http://www.embedinc.com/temp/eusb2_index.txt.  The small black component
> designators only show up on the drawing, not on the board.


This looks very good indeed. You've solved the drawing.assy for Eagle
in this way.
Usually I'm generating a regular silk screen and a modified silk
screen named assembly drawing but is more complicated than your
solution.

greetings,
Vasile

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