Re: short-run PCB fabs

On Wed, 12 Nov 1997 16:36:11 -0500, Joel Rosenzweig <joel-r@an.hp.com>
wrote:

>jwelser@ccwf.cc.utexas.edu wrote:
>>
>> With all this talk about fab-ing PCBs, I'm surprised that
>> no one mentioned doing it at home. The guy who sits next to me
>> here downloaded a PS file with a PCB layout on it, xeroxed it on
>> a sheet of that iron-on resist stuff, and etched it with etchant from
>> Radio Shack, I believe. It turned out better than we both expected.
>>
>> The only limit is on the minimum size of the traces. I think
>> it has to be relatively large (like the size of power/ground traces
>> on video game PCBs.)
>>
>> BUT, looking at Clay's ESB layout, for instance, I think
>> it would be possible to do that at home -- it would just take a
>> bigger board. Not having seen a Quad-Pokey board, I can't even
>> guess if it's possible, but I'm thinking of making my Cine.
>> Exorcisor board this way.
>>
>
>I've done this at home, just like this. I've had mixed results. The
>biggest problem for me at least, was drilling the holes accurately so
>that you could actually fit a 40 pin IC on the board without bending the
>pins every which way. If you are stuffing the board with small IC's, or
>discreet components, the alignment issue is not much of a problem at
>all.
>
>Now that I have a milling machine, I can strap PCB's to the XY table and
>machine the holes to within 0.001 inch tolerances. But, I imagine that
>for most home setups, the drilling step is going to be a continual
>challenge.
>
>I too found that the line widths had to be large for the iron on
>transfer stuff. I guess a little experimentation is in order to figure
>out what you can and cannot do with your particular equipment and
>methodologies.

I have a friend that can get incredibly fine traces (He can get *two*
traces between a standard IC pin.)

He has a few tricks for doing this.

#1 He uses one of those rubber heating pads to "heat the board" not the
transfer plastic sheet. By heating the PCB to transfer temperatures you
don't end up with cold spots where the transfer ink didn't stick.

#2 After pressing firmly (I'm not sure if he even uses an iron, I can
ask him), making sure everything is transferred, he get some chunks of
*ice* and rubs them down the back of the transfer plastic as he peels it
off. The transfer ink immediately snaps of the plastic. He ends up
with a 100% transfer of the transfer ink to the PCB. It's very
effective, by holding up the transfer plastic to a light source you can
see there is *no* transfer ink left on the plastic.

#3 The chemicals that etch the copper are also heated by wrapping the
container in the same "rubber" heating mat stuff, he then uses an
aquarium pump to percolate air through the mixture, to allow for
continuous stirring of the etchant.

#4 Holes are drilled using a small drill press, with the special drills
that are 1/8" stock at the top where they go into the chuck, and are
then tapered down to the very small sizes needed to drill PCB hole. If
you sneeze on these bits, they shatter.

I didn't think a home made board could look this nice, but his boards
come out looking like a professionally done, single sided board. He
also does doubled sided boards, without the plate through holes,
obviously. The give away is the hole spacing, he doesn't have a mill,
and the holes do end up slightly off at times.

-Zonn

<><><><><><><><><><><><><><><><><><><><><><><><><><><><

 ------ ___ Member of A.A.C.S.:
 |---- | ( ) Association for Artistically
    / / ( () ) Challenged Signatures
   / / //\\ // (__)
  / ---/ // \\ //\\ // zonn @ concentric . net
 -------| // \\/
Received on Wed Nov 12 14:06:05 1997