Homebrew PCBs

What are thoughts on exposure time vs. resolution?  Pretend a 100w bulb gives a 10 minute exposure and a 200w bulb gives a 5 minute exposure.  Is either better, worse, the same?

Jeff


-----Original Message-----
From: Boman33 <boman33@...>
Sent: Monday, January 07, 2013 2:41 AM
To: Homebrew_PCBs@yahoogroups.com
Subject: RE: [Homebrew_PCBs] UV nail lamps - sharpness of shadow, phototool-PCB contact closeness, 500W floodlamp

 
Use thicker glass and let the PCB deform to lay flat against it. The force
 of the vacuum (air-pressure) is very large over the big area of the PCB.

 Bertho

 From: Jeff Heiss Sent: Monday, January 07, 2013 01:46

 I experimented with a ziplock bag and a vacuum pump. The transparency is
 held to the board very very well. Much better than glass can ever do.
 However, I found a drawback and that is the plastic forms imperfections and
 scratches from fingernails, stretching and pulling to get wrinkles out
 during vacuum, and around the transparency and copper clad edges.

 I question, as I have not tested, if these imperfections can cause diffusion
 of the light as it passes through and decrease results especially if the
 imperfections are over a thin trace or spacing between traces. I tried
 blanket storage bags, same problem. My conclusion is that very thin glass
 like microscope cover slide glass is the ideal material because it is thin
 enough to deform over the copper clad. I searched for glass as thin as
 cover slide glass but I could not find a place who sells it. Maybe
 something better than ziplock bag plastic can be used too that I am not
 aware of.

 Jeff

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