Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "jerrytr2.com" <jerry@...> wrote:
>
>  It's not quite happening yet.

Here's the basic process I use and get great results with.

Board prep. I scrub the board both sides with dawn dish soap and a 3M
scotch brite sponge (use the scrubby side). I make sure I go in both
directions well (scrub a couple of minutes total) and then I dry it
with a clean white paper towel. If I get any marks on it after that, I
wipe it with 99% alcohol from the drug store.

I still use an iron myself and I get excellent results with it. It's
also easy to place the image on the board and to align images for
double sided boards. I place 3 alignment marks on the layouts (near
the corners, component drill holes can be used as well). I poke a hole
through the holes in each image and then mark and drill these holes in
the board. I then use pins to alight the image to the board, place the
pin through 2 opposite holes and then align the pins to the holes in
the pcb. 3 holes give a third check point or an alternate alignment
point if one seems off. With the image aligned on the board, I press
it firmly with my fingers to hold it there and then tack it down with
the iron. Once tacked down, I place the extra sheet of typing paper
over it and proceed to iron it thoroughly to the board. I use highest
setting, light pressure, and iron for about 3 minutes per side to make
sure it's transferred well. I just place a single sheet of typing
paper between the iron and the transfer sheet, it seems to help the
iron slide without moving the image on the board. I make sure the
edges of the iron pass over the board and around the boards edges but
I never tip the iron, always keep it flat to the board. I never have
any trace adhesion problems doing this. A laminator seems like it
would be nice but my results are good so I haven't bothered with one yet.
For double sided, I let the board cool, flip it over (image & transfer
paper still attached), align the second image using pins and the
pre-driiled alignment holes. Then repeat the ironing process.

The best paper for me has been the cheap office gloss type, A lighter,
semi-glossy paper that has the feel of a good brochure stock. It picks
up the toner well and then breaks down easily in water. The light
weight and semi-gloss let it saturate well and break down quickly. I
had some Epson paper that literally just floated right off but it was
an old pack and I'll be darned if I can find anything like it again.
This office gloss stuff is the next best thing for me. After ironing,
I let the board cool a little and then soak it in warm water. After it
soaks a couple of minutes, I rub it to start it peeling and then
rolling it back, peel most of the paper off under water (it kind of
just mushes a way leaving a thin paper residue). This I let soak for a
time. 10 to 20 minutes probably (I just go do something else and come
back after a while). The remaining residue rubs off easily with just a
little finger pressure. I've never used anything like a toothbrush
(although the foam rubber or a magic sponge is nice some times for
thin gaps, just a light rubbing with it). For paper I'm using the
Hammermill OfficeOne Glossy Paper #229030 (upc 0 10199 16302 8) which
seems to be discontinued. I think it's actually been re-branded as
Hammermill Color Laser Gloss Paper, 300ct #292253 (Sam's number). It's
the same weight, package size, and brightness as the other stuff but I
haven't tried it myself yet. Both Sam's Club and Office Max carry it
(same sources I had for the other stuff too).
My printer is an HP1200 with good rebuilt cartridges. The results are
excellent with this printer. At work we have HP 8000 series. These
also work very well but not quite as good as my 1200 (might just be
the heavy use they see). 

With this procedure I etch in Ferric Chloride and have no problems
with Traces lifting or edge erosion & undercutting. Even when I forget
the board in the etchant for extended periods (usually happens ... get
going on something else and 'Oh, crap ... my board!'). I like to
'float' the board top side down for faster etching and then submerge
it to etch the bottom side (takes little etching as I use planes and
copper pours).

Other tips:  
The wide boarder around the whole board is a good idea, that really
helped me a lot (thanks Stephan!).
I take a small file and file the ridge off the edge of the board.
Sometimes there's one left from the shear process and it can keep the
image from being pressed well.
I use copper pours on both sides (connect to ground). This leaves less
etching (etchant lasts a long time) and gives lots of toner. It may
help with the trace adhesion (like the boarder does).
I apply the toner to a larger board and then cut it to size before
etching (you can do this easily if you cut with a Dremel tool as I do,
I use the emery cut off discs and if you have a steady hand, they work
great ... if not, then you better buy a lot of the discs ;-) ).
I still like the ferric chloride best. It's not as fast as the others
but it's way more forgiving. I had undercutting problems with the
mixed up acids (muratic acid + hydrogen peroxide).

Phil KA0HBG
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