Re: gEDA-user: PCB: coordinates and angles of the components

[Levente Kovacs <leventelist@xxxxxxxxx>]

On Thu, 02 Dec 2010 15:44:34 -0500
Rick Collins <gnuarm.2006@xxxxxxxxx> wrote:

> I'm not asking about the pick point.  I'm asking about the 
> centroid.  They are completely different things.  As I think I said, 
> the centroid is to tell the assembly house where to put the 
> part.  The pick point is a point on the part where the machine will 
> attach the nozzle and has nothing to do with the position where the 
> part is to be placed.  Further, regardless of how you set your files, 
> the pick point is selected by the assembly house to optimize how they 
> pick the part.  You have no way of knowing where this will be.

That is good news.
 
> The centroid needs to be a spot on the part that everyone knows 
> without requiring it to be explained.  Unfortunately for oddly shaped 
> parts, it does not seem to be well understood how to select the 
> centroid.  One document I have from "Screaming Circuits" says it is 
> the center of the part including the pins and the body.  I have yet 
> to be able to find this info in an IPC document.  The IPC document 
> seems to leave out some other important info about rotations.  You 
> would think they would figure out this is a problem and fix it...
> 
> I can't say if your centroids will give you trouble, but from what 
> you are telling me, you are not defining them correctly.  From what I 
> have read, I'm not sure PCB does it correctly either.  I found some 
> references on the web that says they use the geometric center of the 
> pins not including the package.  I don't think that is right.
> 
> Screaming circuits is not the ultimate reference for defining how 
> this is to be done, but they have a document that covers all the 
> bases and is easy to understand.  In fact, when I pointed out that 
> they had a discrpancy with the IPC docs, they immediately fixed it 
> and put the updated doc on their web site.  www.screamingcircuits.com

Okay. Thank you for pointing out all that. I think I'll be fine with the
centroids. It states that the centroid must be the center of the entire
footprint.

It gave me some information about the rotating angle.

I go and tweak my script.

Thank you again,
Levente

-- 
Levente Kovacs
http://levente.logonex.eu




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