One method that is worth trying when using
spray-on resist is to use something like an
old 78RPM photo turntable. You attach the
PCB to the turntable with 2-sided tape and
spin it while spraying on the resist.
In the microcircuit industry, they use a
similar method. The substrate is placed on
a small turntable, and a drop of photo resist is
placed in the middle of the substrate, then
the turntable is spun at a high speed and the
resist spreads out over the substrate surface
in a very evenly distributed coating.
At one time, it was possible to purchase
photo resist in an aerosol spray can, and
it was possible to get a fairly even coat.
But the Feds said that the aerosol was
nasty, so it went away.
Some prototypers have used those little
artists spray guns (air brush) to apply liquid photo resist.
Some of the Kepro systems used the dip-coat
method with a motorized hanger that pulled the
PCB out of the dip tank at a controlled rate, thus
providing a fairly even coat of liquid resist.
There would be a slight "wedge" at the bottom of
the PCB, but it was not a problem.....just make the
PCB slightly longer than the intended circuit board.
Roland F. Harriston
∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗
lists wrote:
>
> In article <f2pf25+oulj@... <mailto:f2pf25%2Boulj%40eGroups.com>>,
> lcdpublishing <lcdpublishing@...
> <mailto:lcdpublishing%40yahoo.com>> wrote:
> > Anyway, I ordered up some negative type resist chemical
>
> If you're talking about spray on type stuff forget it. It's well nigh
> impossible to get an even coating of consistant thickness without
> pin-holes and other flaws.
>
>