Homebrew PCBs

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.
>
> [...]
>