Homebrew PCBs

Vacuum allows you to expose both sides at once, foam does not.

ST

On Fri, Mar 7, 2008 at 12:02 PM, Adam Seychell <a_seychell@...> wrote:
> 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.
>