[MLB-WIRELESS] PCB etching

[Donovan Baarda]

On Wed, 2003-04-16 at 11:10, John Dalton wrote:
[...]
> The basic sequence is
> - Print design onto press n peel film
> - Clean board
> - Iron the design onto the PCB, from the film
> - Mix etchant and dunk PCB in it, stirring a bit until copper has etched away.
> - Wash board
> - Drill holes.
> - Clean board

Another useful step is to put the board into some "tinit" solution to
tin-coat the copper. This makes soldering much easier, and protects the
copper from corrosion.

You can also spray on some protective laquer after soldering on all the
components... it protects the board from corrosion and shorts, kinda
like the solder resist on commercial boards.

> I chose press 'n' peel film as the simplest, but you can also
> use ristron, resist pens, tape, ...
> 
> Anyone out there experimented with running the PCB directly
> through the 'straight paper path' of their laser printer?
> Could save over half the cost that way.

I used the iron-on trick with some success ages ago. This was before the
special iron-on film was available. I tried plain paper and "overhead
projector" film. The plain paper had problems with the toner sticking to
the paper, not the board, and the overhead film had problems with the
toner spreading. You could get both to work, but it required a delicate
balance of not pressing the overhead film too hard with the iron, or
peeling the paper away at the right temperature.

I suspect the new special films make it much easier, but would probably
still require a few goes to get right. They say you can use a
photocopier to put the design onto the film, but I found that most
photocopiers (perhaps they are better now) failed to preserve the aspect
ration and scale well enough.

Double sided boards are very hard to get right. The is no way I know of
doing through-hole plating at home, and without this you need to have
explicit via's that you can solder both sides on... soldering the top
and bottom of dip-pins is a PITA. If the board has lots of fine tracks
passing between the pins of dips, then it becomes nearly impossible to
to do manually.

I haven't done this for years, and to tell you the truth, I'm not sure I
want to. I still have all the gear, but I probably value my time more
than anyone would be prepared to pay. If anyone wants to score some
stuff for doing this, let me know.

-- 
----------------------------------------------------------------
Donovan Baarda                http://minkirri.apana.org.au/~abo/
----------------------------------------------------------------


To unsubscribe: send mail to majordomo at wireless.org.au
with "unsubscribe melbwireless" in the body of the message