Homebrew_PCBs

I don't think I've seen a method described on the list for applying
photoresist film with just a clothes iron, so here goes, apologies if
it's well known.

I start with a board which is of course clean, dry, and cold. The film
is also cold. 10 to 15 degrees C, winter in the shed temperature around
here. Coldness makes it less sticky, at least I feel it does anecdotally.

Plug in the workshop clothes iron and put it on basically the minimum
setting, you'll of course have to experiment to find your particular
comfort zone.

Put the board, copper up, on top of a nice thick piece of cardboard.

Doing the "tape on each side at one corner and pull apart trick" I
remove the entire bottom (inside curl) protective layer.

Now lay the film over the copper, it doesn't really stick cold (at least
mine doesn't) so you can quite easily smooth it on and reposition if
necessary, as you smooth it your body temperature may make the film just
sticky enough to hold in place.

Once the film is in position, flat, and without wrinkles and bubbles,
place a piece of clean paper (or two) over the top of the film & board,
and place the iron on that, covering the board (naturally, this method
is only really going to be good for sizes up to the plate of your
clothes iron, maybe a bit larger).

Apply some pressure, don't move the iron yet.

After say 20 seconds things should be getting warmed up under there,
slide the iron around gently, just like ironing your shirt, paying
special attention to the edges of the board, these are the problem
areas, roll the iron over the edges. Periodically lift the paper and
check the board visually, if it's looking a bit melted, then you've gone
too hot, clean it off (unless it's just an inconsequential spot), reduce
the iron temperature, start again.

Check the temperature with the palm of your hand, you want it nice and
warm, but not so hot that you can't hold it, sort of hot water from your
tap temperature. Once you think it's warm, that's it, slice the board
off (the overhanging film will have stuck it to the cardboard), cool it,
and away you go. If you find that the film isn't stuck to the board
totally, you know that you needed to warm it up more, or more evenly
(spread the iron around), the most likely places to have a problem are
the edges.

I also have an old wallpaper seam roller which I run over the board once
I've removed the iron, just to make sure I've really hit every area with
a bit of pressure especially the edges, but it's probably not really
necessary.

I can do boards quite reliably this way, faster than heating up the
laminator, making a carrier the right size, hinging and taping the film
onto it, feeding it through several times... my clothes iron hits it's
min setting (or a couple clicks above) within a few seconds, and I can
have the film attached in a minute.

Just thought I'd give a quick (well, started out as quick) update on my
further experimenting with "simple" no-laminator application of dry film
using a clothes iron.

Using my multimeter thermocouple function (of dubious accuracy but all I
have to work with) I have found that the iron's plate being between 70
and 80 degrees Celsius seems to work well, of course clothes iron
temperatures wander all over the place, in fact the temperature at the
tip can be 20 degrees or more different to the temperature at the foot,
so definitely have to be conservative with temperature setting.
Somewhere around 100 degrees Celsius blistering seems to start to occur
with any hold time, around 70 to 80 and it appears to be happy for as
long as you want to work it.

Working on top of a piece of paper and after cleaning the board and
smoothing the film on by hand, I place a flat piece of paper or card on
top of the film, then rest the pre-heated clothes iron on top. The
paper/card between film and iron spreads the heat and pressure better
across the "steam holes" in the iron [nb, only iron dry, don't use
steam!], don't use any paper with an imprint (even paper towels) as the
pattern gets pressed into the photo layer easily.

Without moving the iron I wait until the board is up to temperature
(20-30 seconds), then I gently run the iron over the film surface - I
remove the paper/card and just iron directly on the film surface. I
especially run over all the edges with the tip using moderate pressure
(highly recommended to have 1mm border setback on your artwork to
account for "edge problems" anyway), tacking the overhanging film down
onto the surface underneath with the iron both stops the board moving
and serves to pull the film down tight over the edges.

I can even work out small imperfections in the photo layer (even tears
if you messed up removing the underside plastic) by using the iron tip
in a swirling buffing motion to literally "buff that right out". You do
have to be careful not to apply too much pressure, since it's possible
to squish the photo layer enough that it leaves a bald spot (and
subsequent thick area around it).

I can get really nice smooth laminations using this method, equally as
good as using a laminator.

The hardest part of this is getting the film on the board without
bubbles in the first place. What I have learned from many cock-ups is
that that board (and film) MUST be fairly cool, 20 to 25 degrees Celsius
at the most (if you have it too cold, just hold it in your gloved hands
for a few seconds), if you get just the right cool-ness, then the film
will stick when pressed to the board, but can be peeled back again
before ironing if you spot a bubble and need to re-lay it. Too hot and
it sticks forever on contact, too cold and it doesn't stick well enough
to smooth it down at all. Starting too cold is best, your body
temperature can warm it up, start too hot and you will have a lot of
problems.

What works best so far is with cool board and film, to just peel the
entire underside layer off the film and ever so gently drape (float,
waft even) the film over the board, take a piece of cardboard as a
squeegee and place it's edge across the center of the film to pin it to
the board, grab the top edge film overhang and lift the film up
(depending on warmth, it may not have stuck, or may peel off without
difficulty, or if you had it too warm, then it won't be going anywhere
without damage), then squeegee it down towards the top applying
pressure. Repeat the same towards the bottom. Then inspect the board
on a shallow angle and try to work out any bubbles, peeling the film
partially and relaying if necessary (again, cool film, it won't bond
totally and can be peeled at least once).

When doing a double-sided board, I apply and iron one side then it is
absolutely vital to be patient and wait for the board to return
completely to it's appropriate cool temperature before applying the film
to the other side, otherwise it will stick on contact and at that point
you are back at square one (well, you can try cleaning off the bad side
without damaging the good one, Sodium Carbonate solution and a paper
towel, hold the board vertical, and start applying the solution to the
bad side with the paper towel, hopefully you can avoid getting any on
the good side and just dissolve the bad one).

On 31/05/13 01:11, James wrote:
> I don't think I've seen a method described on the list for applying
> photoresist film with just a clothes iron, so here goes, apologies if
> it's well known.
>
> [...]
>