Homebrew PCBs

Etched another board tonight, this is a 4 layer 6/6 board.  After
etching, I noticed that the copper was undercut about a mil or so.
Since the 0.5oz copper is 0.7mil thick, this seems a little high, but
I suppose some undercutting is going to happen.  However, 1 mil per
side on 6/6 gives me 4/8!  Yes, there were some broken traces - I
attribute this to defects in the film lamination, since there were
some.  I ran it anyway, it was my third attempt to laminate film on
the really thin clad.

Do those of you with spray tanks get much undercutting?

Anyway, my observations from this batch:

Agitate during development.  There were some spots that had the flimsy
strands of mask between traces still, I suppose more development might
have helped.  Other spots the mask was fine.

Keep rotating the board during etching so it etches evenly - uneven
etching means some spots get overetched and undercut.

Perhaps I'll bloat the film by a few pixels to try to compensate for
undercutting.

Thanks for sharing the results! Could you put some pictures up if you 
have time?
I'd like to see the undercutting and the board.

I have a Solid wax Ink Phaser8400 and 8-10mil single sided PCB material 
that I run through as paper.
It looks like I will have to preheat the copper. If cold, the copper 
dissipates the post-fuser heat so that sometimes
the wax sits on top, not adhered well.

Thanks, -Lee

Lee Studley <indigo_red@...> writes:
> Thanks for sharing the results! Could you put some pictures up if
> you have time?  I'd like to see the undercutting and the board.

I've already stripped the mask, but with back-lighting through the
microscope it was pretty easy to see what was happening.  I'm thinking
of re-etching that board if I can figure out how to avoid the problem
the next time around.  There were too many of the 6 mil traces that
etched through to bother fixing.

Between the software to print the film and the vaccum to hold it
against the board, I don't think the exposure is the problem.  I still
need to reliably get the film on the blank board (no bubbles), and
figure out developing and etching methods that "always work" without
under- or over- developing or etching.

On Sun, 2009-06-14 at 22:49 -0400, DJ Delorie wrote:

> Between the software to print the film and the vaccum to hold it
> against the board, I don't think the exposure is the problem. I still
> need to reliably get the film on the blank board (no bubbles), and
> figure out developing and etching methods that "always work" without
> under- or over- developing or etching.
> 

You complained earlier about this, the dry film from mg chemicals behave
different than the riston? 
But my big question is, how homebrews that do dry film without the
complete dry film roll properly fitted in the laminator, laminate the
dry film?   

I have tried to use just a piece and stretch it on the board my hand
before pass in the hot roll but I give up. Seems impossible to stretch
it properly without getting air bubbles. The professional laminators
have 3 little things that make this done right.

The only way i know to improve this is Adam Seychell 'wet lamination'
technique, the best thing in his descriptions is not the water but the
really intelligent way he laminate the dry film using a acrylic piece
rubber ended and the water surface tension. Of course that after waiting
some hours the water promotes a very good adhesion of the dry film in
copper but that's not the point.

In dry maybe laminate 2-3cm (ok a inch) of dry film making it stuck in
one end under the hot roll. Stoping the laminator and pull and stretch
the dry film other end in a 45� angle and start the laminator again it
can simulate how good laminators work. But you have to disassemble your
laminator making 90� of the roll exposed, to contact with dry film
before lamination (while stretching).

How do you do it?

Simao Cardoso <simaocardoso@...> writes:
> You complained earlier about this, the dry film from mg chemicals
> behave different than the riston?

Not really.