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.
>
> [...]
>