Homebrew PCBs

>Markus, and others who have done these things on a limited budget:
>Would you please describe your process, or provide a pointer to some
>such description on the web?

Adam and I both have independantly developped a through hole plating
setup. I can't tell much about Adam's (I figure though he will give
you informations) but I do have a page set up that showes the station
I built on my own.

www.myhome.ch/mzingg/pcbstuff/tps

The pages are not absolutely up to date but should give lot's of
information. With my "apraoch" the key point to understand is that I
do not mix my chemicals "on my own" but use the same chemistry as it's
deliverd to board houses. I have mine from Bungard, but it seems like
they have it from "J-Kem International" (who ever this might be). I
don't care cause those huge firms usually don't deliver small enough
quantities as Bugnard does. Another way might be to contact a board
house and ask if they mey sell some of their chemistry. I figure they
may do once they understand that this is about hobbyists use etc.

The remaining part then is to create the tanks and the electronics
needed for agitation and mainly for the electrolytic process itself.

Once these "investments" are made, producing throughplates PCB's
becomes very cheap, painless and fast. All you need is copper clated
material and of course laminate. There is thin copper clated FR4
material available also at reasonable prices. I use 0.5mm for the
inner layer and 0.3mm for the outer layers in case of a four layer
board thereby getting four layer board of the same thinkness as those
made by boardhouses.

The process is not that different from creating double sided PCB's in
that you first laminate, expose and developp and etch the inner layer,
then glue the outer layers onto the two sides. Then you drill holes
(not before this) so as the drill goes through the copper of the inner
layers at those places where it should (the layout must be made so as
the pads don't have holes). If you then through plate this "stack" the
outer surfaces are conneted to the inner layers whre they should. From
this point on there is no difference in createing a double sided PCB,
that said you simply laminate the outer layers, expose and developp
and etch it.

A key point is aligning the layers. I do this with two special
diagonaly psoitioned holes of 3mm diameter that I drill through all
the layers as the first step. The films I use to expose also get those
holes. My english is unfortunately not good enough to describe how I
manage to create precisely positioned 3mm diameter holes into the
films but I "stamp"? them out using a little tool I built by myself.
To create this tool I used 3mm diameter silver steel and used a center
drill to drill a hole into one end. This results in a very sharp edge.
Anyways, once the holse are within the layers and the films, all can
be precisely alligned using 3mm sized pin's. Since I do not have a CNC
drill yet (well, I'm in the process of building one myself but since
I'm currently held busy with other stuff it's laying around for some
months now) I'm actualy laminating a layout to one of the outer layers
at an early stage using a film where the holes of the vias and pads
are not covered. This laminate get's then only exposed and developped
and then serves as a help in hand drilling the holes into the propper
places. Btw, this method of using pin's works so nicely that I also
use it for double sided PCB's to alling the film which before always
used to be a bit trickey.

An important thing is also the glueing. It's very important to make
sure that glue is everywhere and that there are no air inclusions
between the layers. I asure this by glueing both sides in one shot,
applying the glue to the INNER layer only and by only applying a
fairly thinn layer of glue (2 components glue that dryes in 5 minutes
from the hardware store is fine. I.e. 5 min epoxy or similar). The
reason why I apply the glue to the inner layer is that it's structured
by the artwork and by doing so it's obvious that those parts without
copper get enough glue so as there is no air at those spots later on.
After having applied the glue to the inner layer, I position the outer
layers again using the two 3mm pins and apply as much pressure as I
can. I created a little wooden construction for this purpose that
holds two vices positioned in such a way so as I can apply pressure to
an as big area of the PCB as possible. Of yourse, during this process
the PCB is covered by two wood pieces so as it does not get scratched
or bent by the vices and also to more evenly apply the pressure.

That's mostly it. It sounds a lot more complicated than it actually
is. In fact the key point is to have a through hole station. The very
same principle can be used to create 6 layers or more. The only
difference is that you have to glue twice. The holes are however
always only drilled after glueing the most outher layers.

If you also apply a solder stop mask to the outer layers (I do have
one that can be laminated, exposed an developped - again Bungard is
your friend) the look and feel of such a PCB is identical to one made
by a board house. Since I most often use this only for prototypes I
don't apply solder stop mask very often but it works quite well.

>I have made a few small double sided boards using photosensitized
>boards, but haven’t attempted PTH’s or multilayers.

I figure you are in the same boat as most homebrewers here then.

>I have heard of a product that might be of use in making multiplayer
>boards: There are thin sheets of copper on some sort of insulating
>backing material.  The sheets are thin and flexible enough that they can
>be run through a laser printer.  (Small pieces can be cut out and taped
>to a full-size sheet of paper before sending through the printer.)  The
>laser toner protects the copper, so the copper sheet can then be etched
>immediately.  I read about this product and how to use it in a hobbyist
>electronics magazine around 1995.  Some hobbyist supply company offered
>to sell small quantities of the material.  The cost for ten 8 ½ x 11
>inch sheets was less than $100 – maybe much less, I don’t remember.

I never heard of such a product, but IMHO $100 for this size is way
too much. For that price I would have my boards made by a board house.

As stated in my other post, I have a hard time to understand why
people seem to be so shy of using this aproach. Hey, it's nothing more
than 5 tanks with chemicals in them - really no rocket sience to just
use it this way. 

Markus