Homebrew PCBs

--- In Homebrew_PCBs@y..., "grantfair2001" <grant.fair@s...> wrote:
> This group sure looks like a good idea.

A very good idea.

> I also have some old silk screens with old PCB patterns. (Many are 
> from early Elektor projects, though they are not labelled, so I am 
not 
> sure what each one is. I plan to clean these screens and reclaim 
them, 
> unless someone can help me identify the Elektor projects. In 
> exchange I would try printing some of the patterns on PCB's. 
> 
> I think Javex does the trick to remove the old silkscreen stencil. 
I 
> am interested in learning about how to apply new photoemulsion to 
the 
> silk screen, and reproduce PCB art on the silk screen.

I haven't used the Javex product so I don't know about that one.  Do 
you know what photo emulsion was used to create the screens?  If so, 
they should be able to point you to a good reclaiming solution.  I 
have used mainly Ulano products and have had good luck with them.  
Mind you, this was for printing T-shirts and decals but the process 
is identical.

> > I use Ivex WinBoard. Does anyone know if there is a way to laser 
print 
> the PCB pattern to mylar or the like (clear plastic), and use this 
to 
> print to the photoemulsion.? Is there a computer method to turn a 
PCB 
> pattern to a negative one, for laser printing? Is there a 
photemulsion 
> which would respond to a laser printed positive on clear plastic, 
so 
> a negative would not be required?

I have been using the photo process for my boards for a while now.  I 
had very mixed results with the iron on products or even plain 
paper.  I have been able to get very small traces to take using the 
photo process.  I'll give a little info on how I make it work without 
professionally shot film.

First, I am using MG Chemicals, double sided, pre-sensitized boards.  
They aren't cheap but they seem to be rather consistent.  These 
boards are for use with a positive imaged film.

I create the layout and then create a bounding box the same size as 
the blank board I am using.  I can cut the excess board away after 
etching if necessary.  I print two copies of each side of the board 
onto laser transparency.  I then cut the corners and sides off of one 
of the pieces of film for each side so that I can tape them on top of 
each other, perfectly alligned.  This will help create nice dark 
traces so that there is no light bleed through during the exposing 
process.  I align them on a light table making sure that they are 
completely flat and that there are no gaps between the 
transparencies.  I then take a Sharpie marker and fill in the light 
areas on the toner side of each taped together transparency set.  
When I screw up and get sharpie on the clear portion, a Q-tip and 
some alcohol will remove it.  This process will make for a very clean 
film that will expose a board very well with no worries about 
exposing areas where the toner is thin.

After both sides' film are complete, I expose the board on one side, 
using the box printed on the film aligned with the outside edges of 
the board.  This will make both sides very easy to align, as long as 
you get the film the right way up (learned that one the hard way).  I 
also got a scrap of 1/2" thick acrylic to use as a weight to keep the 
film tight against the board during the exposure.  This minimizes the 
chances of light getting under the edges of small traces.

I have had very good success with this method.

Hope this helps,

Chris