Homebrew PCBs

The cover sheet protects the resist from oxygen and from oxidizing the
"free radicals" on which the photo-polymers depend. Here is an excellent
document from DuPont on this:

http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/techtalk/TT1007.pdf

You will note that from an optical standpoint, leaving the cover sheet on
is not optimum as it inevitably degrades the sharpness of the image. This
is one reason why commercial or professional exposure units use arc light
or a similar "point source" instead of diffused light like we home brewers
use almost exclusively. Actually, for the stuff we typically do, the
difference would probably never be noticed.

73,

Todd
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K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
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QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design


On Sun, Jan 13, 2013 at 3:58 PM, Jeff <jeff.heiss@...> wrote:

> **
>
>
> Photoresist is shipped with a clear protective covering film on the top
> and bottom. The covering film is removed by the user before the photoresist
> is applied. A comment by a poster in a forum says the top covering should
> be kept on during exposure and removed before developing. Is that true? Why
> is that?
>
> "Note that the dry film resist should be exposed with the cover sheets on,
> and then held in a dark place for 15 minutes before removing the cover
> sheets and developing."
>
> http://www.electro-tech-online.com/general-electronics-chat/14427-photoresist-pcb-etching-process.html
>
> Jeff
>
>  
>


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