Homebrew PCBs

Hello,

    Having gotten good results with my analog board the other day, I 
proceeded to try double-sided.  Results were mixed....

   This was a little PIC cpu card with a ground plane on the bottom 
and a power plane on the top.  I used the "envelope" procedure from 
Dal wheeler's website.  This worked really well as far as aligning 
the pads.  I added small alignment pads outside the actual board 
area  - two outside each corner.  I then pricked each pad with a 
needle.  Then put the sheets together and pinned them through the pre-
pricked holes onto  a cardboard box.  Then glued them together with a 
Elmer's "extra strength glue stick".

   I was worried that the alignment could be off once I put the board 
in because the board is not of zero thickness.  Maybe one sheet would
stay straight and the other one take up all the bend needed to get 
around the PCB?  But that turned out not to be the case.  Each time I 
tried, the paper flawlessly bent - equal bend on both sheets.

   The laminator was a problem.  My board stock is fairly thick -
 .061".  That plus TWO sheets was a bit more than the GBC95 was 
comfortable with.  It chattered like mad the first time.  And the 
board came out with a big non-adhered area of resist.  Wash and try 
again...

   I took the top off the laminator and removed the screw-spring 
things that tension the rollers.  This time the paper-board-paper 
sandwich went through slicker n'snot.  But still missing resist.  
Wash and try again...

    The third time, I eschewed the laminator and just ironed the 
sandwich.  This was reasonably successful.  A few messed up traces 
around a peripheral chip.  I judged it Good Enough and etched, 
drilled and stuffed. 

                           - Jerry Kaidor

Actually exactly this problem occurs with my homemade laminator. It is
a copy machine fuser and has one aluminum roller (heated) and one
silicone rubber roller.
Because of the different material one side of the paper gets bent the
other doesn't causing misalignment.

The way i found to reduce the problem is to use a folded-over piece of
thin cardboard (cereal boxes work great) to envelope the stack. This
way i also don't need to glue anything.
I leave a few centimeters of spare paper along one edge, this allows
me to press the papers together there while inserting the PCB. When i
feed this edge first it works out most of the time.

Still, they don't always come out well. I very rarely make double
sided, so that is not much of a problem, but also the reason why i
haven't tweaked the process.

ST

On Wed, Dec 24, 2008 at 6:08 PM, jerrytr2.com <jerry@...> wrote:

>
>   I was worried that the alignment could be off once I put the board
> in because the board is not of zero thickness.  Maybe one sheet would
> stay straight and the other one take up all the bend needed to get
> around the PCB?  But that turned out not to be the case.  Each time I
> tried, the paper flawlessly bent - equal bend on both sheets.
>