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 Gerber Offset
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Mike Warren

Australia
121 Posts

Posted - 24 Jul 2023 :  09:32:26  Show Profile  Visit Mike Warren's Homepage  Reply with Quote
I have just completed a revision of a board where the only changes were to traces. No components were moved at all.

This is so the stencil and P&P programming can be reused.

Yet, when I compare the 2 boards in a Gerber viewer I find a slight vertical offset on everything.

http://mike-warren.net/tmp/gerber-offset.jpg

I have confirmed that nothing has been moved in EPC including the origins. I also confirmed this in 2 different Gerber viewers

Does anyone have a suggestion for why this is happening?

http://mike-warren.net

edrees

United Kingdom
763 Posts

Posted - 24 Jul 2023 :  09:53:02  Show Profile  Visit edrees's Homepage  Reply with Quote
Hi Mike,
I had a similar issue that took a little while for even Number One to resolve. This may not be the same issue but I offer it as a suggestion.

My issue involved Mirroring one set of Gerbers and I had a horizontal displacement. This was due to the component "pin names", (although switched off) were to the right hand side the pcb defined area. The plotting command ignores the "pin-names" switched off. Plotting was set to "centred", so the "centre" varies from one layer to the next!

Maybe you have "something" (even if its switched off) outside of the pcb area on only one layer?
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Iain Wilkie

United Kingdom
1009 Posts

Posted - 24 Jul 2023 :  10:59:15  Show Profile  Visit Iain Wilkie's Homepage  Reply with Quote
Not sure if this would be any problem as your manufacturer would normally align everything themselves.

iain
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edrees

United Kingdom
763 Posts

Posted - 24 Jul 2023 :  11:10:18  Show Profile  Visit edrees's Homepage  Reply with Quote
Agreed Iain, but for "Documentation" purposes, it wasn't acceptable. The same "displacement error" occurred with PDF output.

I would have expected the plotting "centering" process to ignore "invisible" items on any layer.
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Mike Warren

Australia
121 Posts

Posted - 25 Jul 2023 :  05:43:49  Show Profile  Visit Mike Warren's Homepage  Reply with Quote
Thank you both for you replies.

I can't see any hidden parts that would explain this.

All I did was change the pinouts of a couple of components ad rerouted the appropriate traces.

Iain, if I don't fix this then the existing pick and place programming will need to be redone. I have no idea if that is easy or hard.

Also, the stencil will mean the solder paste is not quite in the right spot without modifying it in some way. Again, I have no idea what that entails, but can imagine it would require a new stencil.

I'll tried playing with play with the origin and the position settings in the plot dialog, but nothing I could find would make a difference.

http://mike-warren.net
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edrees

United Kingdom
763 Posts

Posted - 25 Jul 2023 :  09:33:30  Show Profile  Visit edrees's Homepage  Reply with Quote
Mike, you could always submit the design to Tech Support who will look at this issue for you.

However, as Iain advises, for Production purposes, its unlikely that you will have to change the Pick & Place file or make a new stencil and the layers can be re-aligned by the manufacturer. A new Pick & Place file is easy to create, but a new stencil could cost $$.

Would suggest checking the X/Y "Plot extents" in the plotting dialogue, -are these consistent with your origin and size of pcb?

(PS. Still think there is a "hidden" item!).
Regards. Ed.


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Iain Wilkie

United Kingdom
1009 Posts

Posted - 25 Jul 2023 :  10:40:11  Show Profile  Visit Iain Wilkie's Homepage  Reply with Quote
I agree with Ed, the manufacturer will simply re-align and aseverything is still in the same "relative positions" this is should be a simple exercise.

I would simply contact your manufacturer to ask them.

iain

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Mike Warren

Australia
121 Posts

Posted - 28 Jul 2023 :  08:07:11  Show Profile  Visit Mike Warren's Homepage  Reply with Quote
Because I'm doing this board for someone else I don't have access to their manufacturer.
As a work-around I created a small rectangle that is positions at the inverse of the error. Now the new Gerbers line up with the original ones.

See picture:
http://mike-warren.net/tmp/gerber-offset-fix.jpg

http://mike-warren.net
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edrees

United Kingdom
763 Posts

Posted - 28 Jul 2023 :  10:08:35  Show Profile  Visit edrees's Homepage  Reply with Quote
Sorry, Mike, I may have understood the problem.

Are you saying that all your new Gerbers layers align with themselves in a Viewer, (and all the old Gerbers align with themselves) but the old and new Gerbers don't align when viewed simultaneously in the Viewer?

It may have been the case that the old Gerbers were originally plotted with different X,Y plot "extents", whereas you may have plotted "Centrally".

I assumed that the image you linked to, referred to two layers of the new Gerber plots mis-aligned.
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Mike Warren

Australia
121 Posts

Posted - 28 Jul 2023 :  21:36:34  Show Profile  Visit Mike Warren's Homepage  Reply with Quote
Yes, both sets of Gerbers were aligned correctly within themselves, but the new Gerbers were not in line with the original ones.

The pin-out was incorrect on the first design. I corrected that for the new revision, which involved rerouting some of the traces.

The plot job used was the same one in both cases.

Anyway, my workaround has solved the problem and I can move on.

Thanks for your input.

http://mike-warren.net
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