Homebrew PCBs

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...