Homebrew PCBs

On Wed, 09 Jan 2013 15:47:35 +1100, you wrote:

<snip>
>This vacuum-sealed bag approach looks inexpensive and effective.
>However, I think it is important to blow air on the PCB so it doesn't
>heat up too much.  Temperature changes could cause the phototool to
>expand at a different rate to the PCB, leading to loss of resolution.
>
>As Harvey White wrote ("UV nail lamps - . . .":
>
>  http://tech.groups.yahoo.com/group/Homebrew_PCBs/message/31264

Actually, I took some scrap MDF and made a vacuum frame.  It's just a
sealed box with an array of 1/4 inch holes in the top.  There's a hole
bored in the side which fits the vacuum cleaner inlet.  The sides are
elevated, forming a U shape.  On top of that U I sit the UV lamp
assembly (fluorescents).  I use an old enlarger timer to control
exposure (it's just a timer, no automatic exposure meter yet).

Harvey


>
>it would also be possible to make a custom-size bag using PVC sheet from
>a furniture store.  Vacuum could come via a small tube inserted into one
>corner of the bag, with the other end connected to a vacuum cleaner or a
>pump from a desolderer.  There's no need for a valve - just run the
>vacuum cleaner while the exposure is taking place.
>
>Since the ~0.5mm PVC is cheap and the bags can be made easily with
>scissors and adhesive tape etc. in sizes which are most suitable for PCB
>work, I think this may be a good alternative to a vacuum frame with a
>flexible top and a solid or foam-and-solid base or to any vacuum frame
>with a rigid (glass or acrylic) top.
>
>The PVC would be less likely to wrinkle or become scratched during use
>than the polyethylene of the vacuum-seal bags.  The PVC is so cheap that
>if it does become scratched, then it will be easy and inexpensive to
>make another bag.
>
>I will write to the list when I try this - which could be a few months
>or more.
>
>  - Robin     http://www.firstpr.com.au/pcb-diy/
>
>
>