I use Scotch Brand Super 33+ electrical tape for board masking.
Unlike many cheaper tapes, it's thin, flexible, stretchable and
consistently sticky. Where I lay two pieces side-by-side, I overlap a
little bit, and I run my fingernail down the line where the tape on
top meets the tape on the bottom. I've never had a leak using ferric
chloride etchant.
I've made a few boards where RF (radio frequency) design practices
required that the top component side be a ground plane. I simply
export the board image into a program like Photoshop or the freeware
Paint.net program, which was developed by Washington State University
and Microsoft. The important thing is that the program must be
capable of doing layers.
I simply create a new layer the exact size of the board image, make it
semitransparent, and copy a bunch of filled circles onto the layer to
the locations where the component leads that are not attached to the
ground plane go though to the bottom layer pads. Then, I turn the
transparency effect "off" (however the particular program refers to
that; in Photoshop, it's variable by percent opacity), collapse or
merge the layers (the board-sized one I created, plus all of the
little layers created by copying the dots), but not the "background"
layer, which is the original board image. At that point the merged
layer can be copied to a new, blank "canvas", which is a new file.
Then I changing the mode on this new image to grayscale and maximize
the contrast (in Photoshop, I just select "Threshold", meaning it's
pure black or pure white). While the layer was transparent, it's
basic color was white, so the image has to be inverted so that I get
the black ground plane with white dots on it.
I then iron the bottom layer onto the board. Once the new ground
plane has been printed, I drill several holes in foil pads where
component leads pass through to the soon-to-be blank circular areas on
the top ground plane. I hold the board and top image up to the light,
align the holes, and iron away, and fix any defects in the transferred
images.
One thing I notice from doing this double-sided procedure the first
couple of times with my Brother 2040 laser printer, just as it's
difficult to get a good image transfer from the paper, or Press-n-Peel
Blue, some degradation of the bottom layer occurs when the board is
heated while ironing the top layer. An image actually gets transferred
to whatever the board is lying on. I never had that problem when I
was using the copy machine for transferring the toner.
Regards,
Ted
--- In Homebrew_PCBs@yahoogroups.com, "sbdwag" <sbdwag@...> wrote:
---snip---
> Right now I do not plan on making very many double sided boards. Its
> more difficult to find single sided pcbs and was wonder how I could
> cover the top side without putting a resist layer on it before I etch.
> Is there a cheap paint that I could spray on it and remove after
etching.
---snip---
>
> Regards
> Wag
---snip---