Homebrew PCBs

On Sun, 10 Jul 2016 22:33:17 +0200, you wrote:

>Gentlemen, 
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>I followed this thread for a while. As far as I remember, I didn't see any attempt to transfer the toner to a pre-heated PCB, just applying pressure with a non-thermally conductive flat surface, (i.e. a piece of wood), hence at Amb. Temperature. My rationale is that we're attempting to stick the toner to a moderated hot surface, applying pressure and hotter temperature to the opposite side the transfer should go. In my opinion, this procedure might result adsorption of the toner by the paper, even with a glossy mag cover, second the paper being hotter than the copper substrate, it looks that things are happening preferably within the paper. Should the board be at the right Temp. (TBD), just before toner melting, the toner should be sticking to the copper instead of diffusing into the paper by capillarity. 

That is one reason that with a laminator, the board is run through
multiple times.  The first few are to heat the board.

I have not seen (although I have not used) normal paper absorbing the
toner.  I think that the toner will adhere to the paper fibers, and
when the paper is soaked, the fibers lose contact with each other, the
paper disintegrates, and you are left with just paper fibers embedded
in the toner.  Because this is done at a low (room) temperature, then
the bond between the toner and board is not likely to be broken unless
the board is scrubbed too hard.

Preheating the board may result in fewer passes, however, if the board
is too hot, the toner will start to smear when in contact with the
heated board.  I (personally) don't do this.  Therefore, I can't
comment on the parameters of that situation, but I suspect that the
board can only be heated so much.

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>The second thing I'm bothered by is the use of a Mylar film for retro-projector as transfer medium instead of paper. Combined or not with my first though. 

I've used a TEK film (once or twice) with poor results.  The concept
is that the toner does not adhere to the mylar film and would rather
adhere to the board.  Whether or not the film is pre-coated with
something that has a limited stick (for toner) is something I don't
know about.

However with Pulsar paper (or the equivalent, if any), there is a
dextrose (sugar) coating that the toner sticks to.  When the paper is
wet, that coating dissolves and there is nothing holding the toner to
the paper, which then floats off.  This depends on the bond between
the toner and the board to be reasonable, but not super tight.

When using glossy paper, the same situation happens but....

the paper coating may or may not dissolve.

if the paper is embedded in the toner, then sufficient scrubbing (or
perhaps just ignoring since the etchant gets around the paper) is
sufficient.

It's the same principle, however, it depends on a number of factors to
determine how effective the transfer is.  That is one reason why all
methods of toner transfer (IMHO) require some tweaking of the process
to be successful.  
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Harvey

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>May anybody point me to threads I missed or are simply these two thoughts not tested yet ? 
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>kind regards
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