I have to agree with Tom: All shops will modify the Gerbers to work with
their processes.
If they didn't the finished pcb features would not match the Gerbers you
submitted.
If you need to add a note it should be something along the lines that no
modifications are allowed except for process compensation.
The note you suggest would likely result in your getting a call from the
shop on every job.
I think the actual problem you have to solve is why did the shop modify
the artwork and then complain about it?
Make sure that is what really happened and that all parties have a
common understanding. There would seem to be a communication breakdown
somewhere.
Greg Smith
On 12/18/2012 4:33 PM, Tom Hausherr wrote:
> Gary,
>
> Typically fabrication shops swell all outer layer features to compensate for
> their etch process tolerance. This has been going on since the beginning of
> PCB fabrication.
>
> I've never heard the board house performing micro-modification, but my guess
> is that might be possible to gain space between conductive etch. A space is
> more difficult to manufacturer than a trace or pad. i.e.: if the space is
> tight to begin with and then the fabrication shop swells the features for
> etch compensation this makes the space between features tighter. So they can
> swell and then micro-modify.
>
> I'm just guessing here because I don't have all the facts, but PCB designs
> often go through the CAM process on the 2nd or 3rd shift. The more notes you
> have regarding "Not permitted without prior approval" will surely postpone
> delivery if fabrication can't contact you at midnight.
>
> I don't know of any IPC standard that addresses this issue. However, I'm not
> sure if a fabrication CAM operator will be familiar with the term
> "Micro-modififications" and they might just throw all modifications into
> that category. So it's best to discuss the terminology with your fabricator
> to eliminate any misinterpretations.
>
> Tom
>
>
> -----Original Message-----
> From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Gary
> Koven
> Sent: Tuesday, December 18, 2012 4:06 PM
> To: [log in to unmask]
> Subject: [DC] Micro-modification fab drawing note
>
> We just had a case of a CM taking it upon themselves to micro-modify
> footprints on source Gerber's and then complain to us about the yield,
> blaming the areas which they micro-modified.
>
> This has motivated us to consider adding a micro-modification note to our
> boilerplate drill drawing layer. This is my first cut at such a note:
>
>
> "MICRO-MODIFICATIONS OR ANY OTHER CHANGES TO CONDUCTIVE FEATURE PATTERN ON
> SOURCE GERBERS ARE NOT
> PERMITTED WITHOUT PRIOR APPROVAL OF (COMPANY NAME)".
>
> There isn't much to go by on this topic in any of the IPC specs or on the
> Web. Please correct me if there's an IPC spec out there that addresses this
> issue.
>
>
> Anyone else who has experienced this, and can improve upon this wording,
> please share.
>
>
>
> TIA and Best Regards,
>
> Gary M. Koven, C.I.D.
> InVue Security Products
>
> Charlotte, NC, USA
> Board Of Directors, RTP Chapter
>
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