Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Many of the of "professional" lab/prototyping PCB exposure units seem to
be fitted with a vacuum assisted frame. I'm wondering if vacuum has much
advantage over conventional sandwiched rubber foam and glass.

These commercial exposure units are built using fluorescent lamps at
point blank range. i.e light goes all directions. I could not think of
better way to promote light undercut. I'm thinking the vacuum on the
more expensive units is put there to help combat non-collimated light.

If the light source is reasonably collimated then does vacuum provide
much advantage ?
Photoresist is about 50um thick. So I guess ideally the photomask should
sit flat on the PCB with a air gap no greater than some fraction of the
resist thickness.