[chbot] Anyone making PCBs?

[Andrew Errington]

Hi everyone,

Have you ever wondered if the 'toner transfer' method of making PCBs
actually works?  Have you ever wondered how you can get the chemicals
needed for etching at home?

I am pleased to report the answer to the first question is yes!  And the
second one is easy.

Sorry to those of you who have blazed a trail and done this already, but
I've always wanted to try for myself.  For a long time.  This weekend I
got started and last night I successfully etched my first board!

There are hundreds of websites describing the process in detail, but in
case anyone is interested I'll summarise how I did it.  Sometimes it is
necessary that 'someone you know' has done it to be the catalyst for you
to try it yourself.

Anyway, here are my key points:

1) I used KiCAD to draw a schematic and design my own PCB.  I'm making a
simple voltage detector which lights a warning LED when the voltage on a
battery pack drops below a threshold.  All the components are SMD.
2) Print a mirror image of the artwork on a laser printer.  There are two
key points here (three, if you count mirror-imaging).
2a) Print onto cheap glossy paper.  I am using a supermarket flyer.  The
paper is thin and flimsy, but has a shiny surface.
2b) In the printer driver set the toner density as high as possible (this
might be set by a 'contrast' or other setting).
3) Clean the copper-clad board really well.  *Really* well.  I am using
the green pan scouring pads (without sponges).  After that, I clean the
board with acetone (I am using nail-varnish remover).  Make sure it's
really clean!
4) I use a clothes iron to transfer the toner onto the surface of the PCB.
5) I let the board cool, and put some warm water in a bowl with a drop of
washing up liquid.  I drop the PCB into the water and wait.  After a while
the toner paper will come away.  After that I soak and rub the rest of the
paper away.  The toner should remain stuck to the board.
6) If all is well you will have toner adhered strongly to your board. 
Touch up any small problems with a Sharpie permanent marker or a needle.

You are ready to etch.

It works for me!  But, it's very tedious to get it right, so persevere
(step 4 is deliberately glib).  If you get a poor result you can wipe the
toner off with acetone and start again.

For etching I am using Hydrochloric Acid 12% (also called Muriatic Acid)
and Hydrogen Peroxide 3%.  I am mixing 50/50, but this will change for
different concentrations.  (Do this in a well-ventilated area, and wear
gloves and safety goggles, and read up on handling precautions).  It takes
about 20 minutes to etch the copper away.

After etching you can use acetone to remove the toner before soldering.

I take no responsibility for damage to your laser printer or anything else
you own, or for injuries sustained playing with nasty chemicals.  I have
skimmed over a lot of detail, so please check the web for more in-depth
info.

Today I will try and solder the components and see if it actually works.

Best wishes.

Andrew