Homebrew PCBs

RM,

Thanks for the reply!

I think you NAILED it!

The boards that I made using the press that were NOT good always had areas that were bad that were not on the edges.  The bad areas were often even symmetrically located, on the board, usually 1/2 to 1 inch or so inboard from each of the shorter ends of the board, and basically centered wrt the other two sides.  So it DOES sound like the (too) thin aluminum sheet was probably being deformed by the pressure, around the edges of the boards, as you thought, causing it to tend to bend upward and away from the boards.

So I am going to look for a thicker, more rigid sheet of metal that I can either lay on top of the boards and patterns, or, maybe, somehow attach to the inside of the lid of the press (which is the heated part), but *probably* only if I can do that without modifying or damaging the press (in case I ever want to sell it, I guess).  I would LIKE to have the metal sheet attached to the lid, though, so that: a) it would stay hot all the time, and b) I wouldn't have to keep handling a large piece of very hot metal.  It might even help with maintaining initial pattern alignment, although, for my other tests, especially with multiple boards, I just used the clothes iron on a corner of each one, for 10 or 15 seconds, to "tack" the pattern to the board in the proper position.

Thanks again, RM!

Regards,

Tom Gootee

http://www.fullnet.com/u/tomg

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Message: 5         
   Date: Fri, 16 Jul 2004 20:47:58 +0000
   From: rmustakos@...
Subject: RE: Anybody tried a large flatbed laminator for toner transfer?

Tom
  It's good to have a lot of pressure, to some extent.  I think the 
problem you are hitting now is that you are applying so much pressure 
that you are distorting the top plate and lossing contact as the top
deforms.  So increasing force on the plate may be decreasing the 
pressure where you want it.
I would try (as others have talked about) 
1) Increase the temp, 300F is about 150 C, which is low end of good.
Crank it up, 350 is still less than 180 C.
2) Back off on the pressure, and put more, stiffer, heat conducting 
plate (Al for steel) on the top and bottom (I say both because I'm 
not sure where your heater is). 
As an experiment, you might try laying out a grid of dots on paper
and fuse it to one of the sheets of aluminun you are using, try it
with a lot of pressure, and also on the other side with less 
pressure.  Check to see if it holds better on the edges than in
middle.  If it does, you might want to look at some type of curved
surface, convex up, highest in the center, with which to support
your boards.  I bet laminate glue is much more forgiving of
pressure than the toner is.
Good luck,
RM




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