RST Engineering wrote:


MAKING THE CIRCUIT BOARD

WEll, you just blew my August Kitplanes article out of the water.

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Dear Jim,

Not a problem. No one actually READS these posts to rah :-)
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But the paper
HAS to come apart if we want to leave ONLY the thermo-plastic material
bonded to our circuit board. So use the cheap stuff. And soak it in
warm soapy water. Then scrub it with a tooth brush or whatever -- get
ALL of the paper off of the thermo-plastic.

One of those green kitchen pot scrubbers does a pretty fair job getting the
paper off while leaving the toner on the board.

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Agree.

Initially, I went at the paper in a very tentative way, worried that
any amount of scrubbing would remove the toner. Which is something of
a joke. If you've used enough heat, the toner STAYS, despite scrubbing
with everything that came to hand.

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Now you can etch the board in the usual way.

Or you can use the new, improved way without that nasty ferric chloride.
Plain old swimming pool etchant (muriatic acid -- 28% HCl) from the home
store plus plain old hydrogen peroxide (3%) from the drug store mixed 2:1
respectively does an admirable job at room temperature.

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Having several jugs of ferric chloride on-hand (plus a heated, rocking,
etching tank), I'll stick with what I know.

If you use acid, make sure it's compatible with the substrait; some
phenolics are not. And be sure to neutralize the BOARD after etching.

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The result is a bright copper circuit board

Made even brighter if you use Copper-Brite from the supermarket and the
aforementioned green pot scrubber.

You might also google on "Tinnit"....
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....or simply paint the exposed copper with clear fingernail polish,
dilute epoxy or whatever.

I've found the main advantage of 'Tinnit' and other circuit board
plating schemes is that they prevent corrosion BEFORE the board is
populated & soldered. Once the board is finished, anything that serves
to seal the surface from the air will prevent corrosion, assuming the
original etchant and solder flux was not. Plated boards make good
sense when you run up a batch then dole them out over a period of years
-- the plating keeps the exposed copper from corroding, especially if
you've kitted the board with other components, some of which may
produce corrosive fumes (ie, certain types of capacitors, some
plastics, etc).

The LED nav lights are a continuation of the series of articles about
Flying on the Cheap. I assumed the folks who make them would populate
& solder the board immediately after etching, hence no mention of
'Tinnit' or other plating. In fact, I've assumed folks would want to
keep the cost down, using whatever etchant they could pick up from
their local Radio Shack (probably ferric chloride) and sealing the
board with clear fingernail polish, for which a suitable REMOVER is
commonly available. (Seal a board with epoxy, if you need to work it
in the future, you're pretty well screwed :-)

In closing, someone else has already mentioned an excellent article on
the subject of generating circuit board masks using a laser printer. I
arrived at the process by a slightly different route in that I was
making faux 'antique' astrolabes and needed a method of etching Arabic
and Chinese characters onto brass plates. In developing that method I
also used it to do nomenclature on instrument panels and rivet-on data
plates, which I feel deserves mention.

Not only does this method allow you to make near-perfect reproductions
of data plates and the like, it allows you to etch logos, names and so
forth onto aluminum tool boxes, prepare 'engraved' plates for
presentations, and so on. The tricky bit here is that you are
typically etching in the positive sense rather than the negative. I
found the best way to do this was to make individual masks -- OIL
PRESSURE -- 10 A -- TACHOMETER ...or whatever. The characters
themselves are left clear and the mask is cut to leave a border of
toner. These masks are then ironed on to the panel, plate or whatever
in the usual manner. (Large pieces, such as a tool box or instrument
panel, will benefit from being pre-heated.) Once the masks have been
transferred to the work-piece all of the open areas are sealed with
something that will resist the etchant; regular enamel paint works
okay.

This is a case where acid has a definite advantage, since the object is
to remove a signficant amount of metal.

Once the piece is finished, the etched areas may be filled with a
contrasting paint.

The joke here is that I spent a couple of years making instrument
faces, 'antique' compases and the like before I realized the method
could also be used to make circuit boards :-)

-R.S.Hoover