Homebrew PCBs

Phil wrote:
> ok, I got some of the office max photo paper.  so far, with three 
> tests, I'm underwhelmed.  I think it might require a higher 
> temperature - the toner was staying with the paper in places.  This 
> is at the same temp setting that I use for magazine paper.  That 
> suprises me - I expected the toner to melt at the same point and 
> adhere to the copper, regardless of the paper.  I'll try again 
> tomorrow when my acetone induced fog clears. lol
> 
> --- In Homebrew_PCBs@yahoogroups.com, Alan King <alan@n...> wrote:
> 

   Ack, I was expecting to have a bit more discussion on the paper before you 
got some lol!  :)  I should have pointed out earlier there are a lot of papers, 
as in:

http://www.jetprintphoto.com/c/index.asp

   The one I use is in the lower left, the purple one.  The green one in the 
upper right is one of the closest to it in paper construction, but even it gives 
noticably different results.  Easier seperation and peel, but more pinholes etc. 
  So minor seeming differences can affect the results.

   Still, you should get a reasonable result with almost any of those papers, 
even if it's more or less perfect.  And the Office Max products are coming out 
of the same plants just with a different printed jacket, so has to be something 
similar.

   And yep you'll need more heat.  With magazine paper, you have a thin 
compressed paper with solid coating.  Ends up being basically solid coating 
pressed through and through, with just some paper fibers in the middle to hold 
things together.  Solid like that conducts heat very well.  Instead you now have 
a thin solid coating, but with normal paper backing which is much more 
insualative.  You won't get the near instant heat transfer that you did before, 
the other side of the page will likely be cooler than the iron for quite some 
time as it heats up.  Also with the near solid page before your pressure may 
have been doing a lot of the transfer, along with why you were getting the 
mashing.  Pressure will be moderated a bit more with the thicker paper, so you 
have to get good heat to the other side of the page and let heat do more of the 
transfer.  The toner does still melt at the same temps, it'll just have a bit 
slower curve getting the heat through the paper, and since the pressure is a bit 
more moderated it can't be rushed with more pressure, which you may have been 
doing inadvertently with the mag paper.  This will take a bit more time to get 
to the 160 or 180 most toner melts at.

   I just set my iron to hottest, and then on a smaller board press the iron on 
for a few minutes moving around now and then.  Not the most pressure I could, 
but probably 10 ot 20 lbs or so at least for a while during the ironing.  I do 
it on a board on the carpet, with a couple paper towels under the PCB to help 
keep it from sliding so much with the slick board.  At the beginning pressure 
doesn't matter so much, you're still heating up the paper and board etc and the 
toner isn't melted.  Cut your board down first so there's less copper to conduct 
heat away if you're not already.  Try 4 or 5 minutes with a hot iron, should be 
extra but should at least make sure you at least get a reasonable transfer to 
start with.  After a point the toner was already transferred, and you're mashing 
it back into the paper.  But a little longer to start with and then shorten as 
you get a feel for things will probably do better than too little.  And yep 
sounds like you had it a bit too short from your magazine paper experience.

   Also note with the magazine paper being solid and slick you can get away with 
just a straight peel after cooling, so you may not have even been wetting it so 
not sure if you were or not.  With this, wait a few minutes for the board to 
cool a bit so the toner is back below melt temp.  I tend to blow on it or wave 
it around a bit to help speed this up.  Then wet with medium hot water for a few 
minutes (less thermal shock so maybe less forces on the toner, the paper will 
shrivel a bit and be putting some sideways forces though), fill the sink a bit 
and let it soak.  Then I run cold over it a little bit to solidify things, then 
peel under warm.  As you're peeling have the water hitting the surface between 
the board and paper, to soften things if there were any dry spots from air 
bubbles etc.  I used to soak it for a long time, but have found that's not 
necessary now, but it needs the extra fusing part so the unprinted coating 
doesn't stick during the peel.  Without that even soaking for 24 hours wasn't 
enough to keep a lot of the coating from sticking in the holes and between 
traces.  The extra fusing seems to bake the coating a bit, and then it doesn't 
stick during the ironing part.

   And LOL yes acetone is magic stuff.  Try using a plastic pad and alcohol to 
clean the toner from a board if you haven't already, it'll give you a whole new 
level of appreciation for what a joy acetone is to use.  Acetone converts what 
seems like hours into just seconds, who knew it was a time machine component?

Alan