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 Post subject: pattern origin vs. pick and place (new user)
PostPosted: 29 Sep 2011, 14:42 
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Joined: 16 Aug 2011, 15:23
Posts: 10
I'm foggy about how the PWB assembler determines the index location / orientation for components for pick and place.
I don't understand how this is resolved vs. the (diptrace) origins on the patterns.

1. Is the origin I use when I create a pattern totally arbitrary, because the origin, relative to pad locations, is transmitted in the fab files, and thus resolved downstream?

2. Or.. is there a rule I must follow about when I locate the origin in order for the parts to be placed correctly on the PWB?

Thanks in advance to anyone who can clarify this for me.


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 Post subject: Re: pattern origin vs. pick and place (new user)
PostPosted: 30 Sep 2011, 08:01 
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Technical Support

Joined: 14 Jun 2010, 06:43
Posts: 2762
When you export pick and place file, you have a choice what point should be component origin. It can be component center (calculated automatically) or component origin.
If you used standard libraries or designed patterns due to IPC recommendation, export pick and place file by origin. Otherwise, if origins in your patterns are in arbitrary positions, export pick and place by component center.


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 Post subject: Re: pattern origin vs. pick and place (new user)
PostPosted: 07 Oct 2011, 20:34 
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Joined: 16 Aug 2011, 15:23
Posts: 10
I think I was confusing the 'centroid' with the PE 'origin'. If I export a pattern to ASCII, I can see that moving the PE 'origin' around has no bearing on the pad coordinates in the LIB output (the only thing that changes , besides 'OriginX' & 'OriginY' are the params for the 3D view). This suggests that the "origin" is really just a arbitrary reference to give the user the ability to define the relative position of objects.

But.. this contradicts your advice above, recommending that my choice of export should be based on origin = 'auto' or arbitrary.

I read on the net that the 'centroid' of a part, IPC-wise, is defined as the mean of ea. of X,Y of all the pads in the footprint. Can you confirm? If so, it is strictly a function of the pad coords and hence no independent definition is possible.

For patterns that are symmetric in both axes, the 'mean' definition and the auto 'origin' within PE produce the same result. However, for non-symmetric patterns they do not.

For some footprints, it is very useful to use a non-auto origin for inputting objects (e.g., off a CAD drawing). But when I'm finished, what then? Convert the origin to 'auto'?

When I started creating footprints I was winging it. Then I learned about IPC7351 -- that there are conventions I should follow. If I'm mixing my own FPs with those from your libs, it would seem I need to be consistent in order for things to go smoothly at the board house.

To achieve that goal, what exactly must I do in PE, other than observe the rules for orientation (0 deg rotation), polarity, etc., to insure that the FPs I produce are (IPC) compliant- & consistent with your libs?

I couldn't find any guidance in the PCB help file, so I hope you don't mind my asking these questions.


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 Post subject: Re: pattern origin vs. pick and place (new user)
PostPosted: 10 Oct 2011, 06:47 
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Technical Support

Joined: 14 Jun 2010, 06:43
Posts: 2762
It seems you dig too deep. Why do you explore ASCII file?
In most cases, exporting pick & place file by component center and origin give the same X Y coordinates if patterns were centered in libraries. It is true for symmetrical components. For non-symmetrical ones, you may want to define custom origin because centroid of this component isn't in component center. In that case, exporting p&p file by origin is preferable.


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 Post subject: Re: pattern origin vs. pick and place (new user)
PostPosted: 19 Nov 2015, 08:27 
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Joined: 22 May 2015, 02:26
Posts: 5
One issue I found using 'center' instead of 'origin' for the pick&place file is that the center is apparently computed taking into account all layers, including the silk layer.

So for example, a standard DIPTRACE diode pattern will have its center shifted toward the cathode mark.

I think that the center should only be computed with the signal layers, plus maybe the assy layer ?


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