Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@...> wrote:
>
> yes to all your questions.
> 
> Edge problems are common. There can be many reasons, like
> contamination or bad surface preparation, which is tricky along the
> edges. Also, the pull from the paper shrinkage under heat is 
greatest
> on the edges.
> I simply leave a solid copper border around the PCB (or around the
> outside of several if i make more than one on a panel), and cut it
> away later. It is the only sure way i have found. Apparently
> pre-shrinking the paper by running it through the laminator before
> printing has also brought relief to some.

*** I tried this.  Sure can get some serious shrinkage with a full 
sheet.  In fact, the paper ( HP Q2419A ) just wrinkled up.  Obviously 
wouldn't have worked at all.  

    I tried again this morning.  Used a board about two inches
too big in each dimension - so there was an inch of dead space on 
each side.  I printed onto the HP glossy paper with the following
settings on my Brother MFC8600DN:  
  * resolution 1200HQ
  * "transparency" ( figured those are smooth, and the printer might
    put down more toner )

   I cleaned the board with laquer thinner, and then with denatured 
alcohol.  Trimmed the printout a bit smaller than the board, and 
taped it on with Scotch Magic tape.

   Gave it 5 passes through the laminator (GBC 95P ) doused it in 
cold water, and then  let it in hot soapy water for about 15 minutes.
It mostly worked, although the corners were still crumbly, and I had 
to spend about a half hour rolling the soft paper off.

   Bits of toner were coming off in the ferric chloride bath.  I 
fished the board out and touched up with a fine-tip marker pen.

   The circuit side etched faster than the back side, so when it was 
done ( and the back side still had a ways to go ), I taped off the 
whole circuit side with masking tape and finished etching off the 
other side.  It's not pretty, but it'll work.

   Things I want to try next time:

   * Sand the board.  I think that a bit of a tooth will help the 
toner stick.  Say 400 or 600 grit.
   * Try different temps.  I think maybe the "foil" setting is a bit 
hotter than needed.  I noticed some pots on the circuit board in the 
laminator.  A lower temp should help with the shrinkage.  Would like
it hot enough to melt the toner, but no hotter.

                           - Jerry