I use a screen printed soldermask that is UV cured. There are many
suppliers of this ink and mine is made by Taiyo. We make a silksceen
using Autotype Five Star indirect film emulsion on a 180 mesh screen
fabric. Aluminum frames should be used for best results since the
wood types can't hold the required screen tension for very long.
Taiyo also offers a liquid photo imageable mask. The circuit board
is "flood coated" using a blank 110 mesh screen and then cured at 180
degrees F until "tack free" but not fully cured. A film positive is
then used to expose the required pattern. The exposed panel is
developed in a 1% soda ash solution. After development the panel is
baked at about 300 degrees F for 45 to 60 minutes.
DuPont used to make a dry film solder mask. We used their 8140 series
dry film solder mask but I don't think they make it any longer. The
liquid photo imageable types have taken over the market. It's very
difficult to apply these dry film masks without using a vacuum
laminator. We never did care much for the results and this was after
wasting $48,000 on a DuPont vacuum laminator. The liquid types work
much better.
The only time anyone really uses the dry film masks now days is when
they need to "tent" or cover over drilled holes with the exposed mask
which is rare. Dry film and liquid photo imageable solder mask both
require a huge amount of UV power to expose them properly. We used an
ORC 5 kW exposure unit for this purpose. It had water cooled lamps
since the heat from the lamps could damage the panel being exposed.
If the board gets too hot during exposure the film photo tool will
stick to the panel and make a big mess. By water cooling the lamp
only the UV light gets through and the films don't stick.
I think the silk screen method would be the best way to go for the
home shop. You can cure UV screen printed inks with a mercury vapor
lamp or just print the two part epoxy solder mask that is cured in a
regular oven.
Tom
--- In
Homebrew_PCBs@yahoogroups.com, "Zoran A. Scepanovic"
<zasto@y...> wrote:
> Hello Markus,
>
> 22. May 2003, 22:35:57, you wrote:
>
> MZ> Hi Marty & Steve
>
> MZ> Thanks for the pointers. I'm willing to take some effort to get
a real
> MZ> solder stop mask.
>
> MZ> @Marty - I would be especialy interested how the dry film
solder mask
> MZ> technique works. I'm ready to let some dollars roll. I usually
don't
> MZ> need a solder stop mask since I'm hand soldering my prototypes,
but
> MZ> there are ocasions where I must create a prototype in a short
time
> MZ> that should look like one made in a board house and where time
does
> MZ> not allow to have it made externally. Could you therefore
elaborate a
> MZ> bit on how this is done, what equipement is needed, what a
simple one
> MZ> would aproximately cost and possibly where to get it?
>
> MZ> @Steve - thanks for the pointers. I defniately will go through
them.
>
> MZ> Markus
>
> www.thinktink.com
>
> This is the place where you can spend some of your $$
>
> A little bit more at:
>
> http://www.thinktink.com/stack/volumes/volvi/pholam.htm
>
>
> --
> Best Regards,
> Zoran
> mailto:zasto@y...