Bob,

This analysis was extremely helpful.

I started working my way through the presensitized boards the last time I
was on this roller coaster but did not complete the job. Let me run a brief
description of what I have read and see if there are any errors in my
thinking:

1) Print mirror of circuit onto transparancy sheet at max toner setting.

2) Bind sheet face down (and flat) to presensitized board. Cover with real
glass as it is transparent to UV. Do this in a low light environment.

3) Expose assembly to UV light. Sunlight will work but a UV light box is
better. Mine is a black light installed in a toolbox. Never got a clear
number on exposure time. Seems to be trail and error but consistent once
you get it to work.

4) Peel the transparancy and there should be a outline image of the circuit
on the board. Run the board through the developer (some say caustic/washing
soda is OK, others hate it. Suggestions?) until the exposed parts a
removed. Do not do it too long or risk undercutting the solid unexposed res=
ist.

5) Etch the board.

6) Remove the rest of the photoresist. A bit unclear here. Is this a light
and develop a second time step? Or a physical process

Should be ready to shake and bake after this.

On this recommendation, I will attempt this method first. There seems to be
repeatability issues with the toner transfer method.

Thanks for the input.

BAJ


On Mon, Mar 21, 2011 at 06:43:57PM -0400, Bob Blick wrote:
> On Mon, 21 Mar 2011 18:32 -0400, "Byron Jeff" wrote:
>=20
> > I'm planning on testing both the Toner Transfer and the Photo resist wi=
th
> > precoated boards. Both seem to be about the same amount of time in term=
s
> > of
> > speed. Overall the TT method seems to be cheaper as precoated boards se=
em
> > to run about 3x the cost. So it seems to me that the real question is
> > process repeatability.
>=20
> Hi Byron,
>=20
> I've tried using an XY pen plotter directly to PC board and never got
> good enough etch resistance. All over the net there are recommendations
> for the RED Staedtler Lumocolor pens but even they are not good enough.
>=20
> I have used spray-on photoresist. It's OK except for the hairs and dust.
> In other words, not good for fine pitch because you will have bad spots.
>=20
> Laser toner transfer is sensitive to your ironing pressure and
> temperature. I always print a border around my artwork to act as a
> pressure buffer. It seems to even out the pressure near the edges. Fair
> to good results if you have finesse. Prepare for lots of do-overs and
> some touchup before and after etch.
>=20
> Presensitized board works really well. No question, this is the way to
> go if you want quality. And unlike the other methods it takes very
> little talent. Your first board will be good and every one to follow.
>=20
> I tend to do toner transfer because I am drawn to how immediate it
> seems, and the fact that you don't really need any consumables. But then
> after I have ironed on and cleaned off the same board three times before
> I get a transfer good enough to etch, I rethink my choice of technology,
> wishing I'd used presensitized board instead. And it's not like there
> are no consumables, I use acetone to clean the board and lacquer thinner
> to remove the toner.
>=20
> Note to self: Since I don't make more than a dozen boards a year I
> should always use the presensitized board.
>=20
> Cheerful regards,
>=20
> Bob
>=20
>=20
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>=20
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--=20
Byron A. Jeff
Department Chair: IT/CS/CNET
College of Information and Mathematical Sciences
Clayton State University
http://cims.clayton.edu/bjeff
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