Homebrew PCBs

Hi Group,
After some inconsistent results on retouches and second-side masking,
I did some test using some common pens and other materials.

The photos of the steps in the tests, along with my conclusions, are
in the Photo section, album Ted-KX4OM.  The best results for
retouching, which should not be surprising to the group, were with
Staedtler Lumocolor permanent pens, specifically colors blue and red.
 On each of the pen tests, I wrote some text normally, drew a line
underneath, and went back and heavily "dotted" in a second layer of
ink for the first half of the line.  A liquid Stylist Black pen look
superb on unetched copper, but, alas, it turned out to be water based
and immediately washed off.

The other test was for masking large areas, such as the second side of
a board, either as-yet unetched, or previously etched.  Of the tapes
and liquids, only Future Floor finish did not give good results.  One
problem, yet unsolved, which was not part of the test, is performance
of tape when it has to overlap for coverage.  I've been getting some
seepage  under the overlaps at the edge of the boards using 3M 33+
electrical tape.  The liquids (and the pen ink) were allowed to dry
overnight.

It occurs to me that if using one of the more flowable liquids, such
as Spar Varnish, the liquid should be applied to the second side and
allowed to dry prior to drilling alignment holes.  Otherwise, the
liquid will likely flow through the holes.  This would almost
guarantee that the varnish, etc., would stick to whatever surface
(paper towel) while ironing.  It shouldn't cause a problem with the
more easliy removed liquids, however.

Another problem, which may be the next test I do, is retouching toner
traces with the more successful pens.  With my Brother HL-2040 laser
toner, I've had problems with Lumocolor red when thickening a
weakly-transferred line.  It appears that there is a reaction or
something that causes further erosion of the trace while etching.

All my tests and my production etching are done with room temperature
ferric chloride, typically for 20 minutes under a 60 watt lamp,
rocking the pyrex dish constantly as the etching occurrs.

Regards,
Ted

On Sat, 30 Sep 2006 16:42:49 +0200, kilocycles <kilocycles@...>  
wrote:

>  One
> problem, yet unsolved, which was not part of the test, is performance
> of tape when it has to overlap for coverage.  I've been getting some
> seepage  under the overlaps at the edge of the boards using 3M 33+
> electrical tape.


I found the problem goes away if i rub the overlap with a fingernail to  
close it up. I used thin PE or PP tape.

Best seems to be to avoiding to mask stuff at all, simply etch both sides  
at once.

ST

Hi Stefan,
I had been using 3M 33+ because it is very stretchy compared to other
electrical tapes, and it conforms well. I have been running my
fingernail along the overlap.  Based on your comment, I'll look for
some thinner tape.

I have to use so much heat with the Brother toner, it re-transfers off
the copper to the paper towel or whatever I use under the board if I
do both sides before etching.  I wonder what wax paper would do? Wax
might act as a resist, though. Something Teflon coated, maybe.

As to the heat, I've been using a piece of ceiling tile between my
iron and the paper towels and the plywood bench I've coated with
sanding sealer.  The heat is so great that the tile transfers through
the tile to the plywood finish!  I glued some construction paper to
the tile as a backing with 3M super adhesive (contact cement), and the
cement melted and transferred.  I think I need to use space shuttle
tiles, or aerogel, or something as a work surface :)  Actually, bare
plywood would be better, I think, since it's not flammable.  I'll put
a couple of bricks under a piece and try that.

Regards,
Ted
--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
<stefan_trethan@...> wrote:
>
> On Sat, 30 Sep 2006 16:42:49 +0200, kilocycles <kilocycles@...>  
> wrote:
> 
> >  One
> > problem, yet unsolved, which was not part of the test, is performance
> > of tape when it has to overlap for coverage.  I've been getting some
> > seepage  under the overlaps at the edge of the boards using 3M 33+
> > electrical tape.
> 
> 
> I found the problem goes away if i rub the overlap with a fingernail
to  
> close it up. I used thin PE or PP tape.
> 
> Best seems to be to avoiding to mask stuff at all, simply etch both
sides  
> at once.
> 
> ST
---snip--

On Mon, 02 Oct 2006 01:28:16 +0200, kilocycles <kilocycles@...>  
wrote:

>
> I have to use so much heat with the Brother toner, it re-transfers off
> the copper to the paper towel or whatever I use under the board if I
> do both sides before etching.  I wonder what wax paper would do? Wax
> might act as a resist, though. Something Teflon coated, maybe.


Simply do not remove the paper from the other side. I used to align two  
papers, put the PCB in between, and feed the stack through the fuser to  
transfer both sides at once.

You could also try a silicone or teflon baking sheet...


ST

> > I have to use so much heat with the Brother toner, it re-transfers off
> > the copper to the paper towel or whatever I use under the board if I

Odd that you use so much heat, I was having problems with the toner
not transfering to the board so used ore heat, it got better, I then
'uprated' the thermostat in my iron with brute force, it got worse! I
bent it back and ended up cooler than when I started, and its been
great ever since.

Original hp4l toner cartridge and 'kodaper' photopaper, although
asda(walmart) instore magazines have been good for me lately



-- 

Lez