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Re: [PATCH] - PCBNEW - implement PS plotting width correction.


I didn't know it either and Brians' explanation did not explain it to me fully (sorry Brian), so I decided I wanted to know.

I found this page (http://www.standardpc.com/engineering.htm) where they say:
**Etch factor is a reduction of line width due to the etching process.  The sides of the copper trace are exposed to the etching solution as the unwanted copper is removed from the surface.  The amount of reduction is dependant on the thickness of the base copper cladding.  For example: A 10 mil trace may be reduced 0.5 mils when etching 1oz copper clad or 1.0 mil when etching 2oz base copper.  Staying within 20% of nominal trace width as specified by IPC is not a problem with standard copper weights.  If heavier copper weights are used then compensating the line width may be required to maintain the 20% tolerance.  For a 12 mil line utilizing a 4oz copper base, it would be advisable to compensate the designed line width by 2 mils to allow for etch factor.

A similar situation exists with RF designs where line width tolerances are critical to the function of the board.  Typically we will compensate line widths as necessary to achieve the designed line width (as taken from the gerber files) after etching.  If you would prefer to compensate the line widths yourself, please notify us so we do not over compensate.

Happy NewYear,

On Dec 30, 2011, at 9:05 PM, Brian F. G. Bidulock wrote:

> Dick,
> On Fri, 30 Dec 2011, Dick Hollenbeck wrote:
>> Hi Alexander,
>> It would have been nice to explain your strategy and why you chose this over possible
>> other alternatives.
>> Can you pllease explain:
>> What is width correction?
>> Why do you need it?  That is, what is wrong with the original width that it needs
>> "correction"?
>> Why is the original width wrong?
>> Thank you very much,
>> Dick
> The correction is for etch factor.  PS is the final plotting
> stage in toner transfer method.   The PS image will be tranfered
> to the board directly as an etch resist.  Widths of tracks and
> vias must, therefore, be "corrected" for etch factor.
> --brian
> -- 
> Brian F. G. Bidulock    œ The reasonable man adapts himself to the œ
> bidulock@xxxxxxxxxxx    œ world; the unreasonable one persists in  œ
> http://www.openss7.org/ œ trying  to adapt the  world  to himself. œ
>                        œ Therefore  all  progress  depends on the œ
>                        œ unreasonable man. -- George Bernard Shaw œ
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