42 Silicon chip Australia’s electronics magazine siliconchip.com.au
ers are suitable for this conversion.
There are some challenges to mill-
ing PCBs. To get good results, the PCB
must be very flat and level, as the mill-
ing depth will vary if the PCB is not
entirely flat. Some mills can compen-
sate for this.
Software for milling PCBs
Appropriate software is also re-
quired to convert Gerber files to a lan-
guage that a 3D printer understands;
typically G-code.
G-code is a slightly different subset
of RS-274 than that used in Gerber
files and is commonly used in CNC
applications.
We found two programs which can
do this, but since we don’t have a mill,
we couldn’t test them fully.
FlatCam, mentioned earlier, is a very
flexible and powerful program, and it
can do the Gerber to G-code conver-
sion that is needed to create a PCB us-
ing a mill – see Fig.9.
Another suitable program is pcb-
2gcode, found at: https://github.com/
pcb2gcode/pcb2gcode
This has a much simpler command-
line interface, although a graphical
version is available.
Making PCBs with a laser cutter
There are a couple of different ap-
proaches to creating PCBs with a la-
ser cutter. One uses the laser to react
with a photochemical resist layer.
Rather than using a mask, the resist is
directly cured by a pass of the laser. It
appears that the software to do this is
straightforward.
We used gerbv to export a PCB lay-
er in Gerber format as a PNG image,
then imported this file into our laser
cutting software. We then cut a scrap
of acrylic as a test. The results can be
seen in the photo below.
Because many CNC laser cutters are
used to do engraving, the software is
almost always capable of importing
image files like this. Despite how easy
it is to do this, we would be dubious
to recommend it without further re-
search into the specific chemicals be-
ing used and how they might react to
being hit by laser radiation.
That’s why we tried it on a piece of
perspex and not a PCB.
For example, it’s well known that vi-
nyl should not be cut in a laser cutter
as it releases toxic, corrosive chlorine
gas which will poison you and dam-
age your laser cutter. Any compound
that contains chlorine will have a
similar result.
Also, you will have to tune the
speed and laser intensity to get a
good result, and in doing so, if the la-
ser power is too high or cutting speed
too low, you could cut through the
etch-resist layer, with unknown con-
sequences.
Another variation we’ve seen,
which may be more practical, is to coat
the copper clad board with black paint
and using the laser to blast it away to
match the negative of the PCB pattern.
The remaining paint forms the etch-
resist mask, and the board is etched.
In this case, the development step is
not needed.
If you have an industrial power laser
cutter, it may even be possible to sim-
ply vaporise copper off the board, pro-
ducing PCBs in a single step. Drilled
holes could also be completed by hav-
ing the laser linger a little longer!
In brief, a laser cutter could make a
great tool for producing PCBs, but we
have our doubts as to the safety of the
process, both for human and machine.Printing circuits on other
substrates
We mentioned that the Voltera V-
One PCB Printer can print on glass or
even flexible substrates. PCB manufac-
turers can also create aluminium-core
or flexible PCBs at a price.
We’ll mention some techniques we
have seen which allow hobbyists to
create their own PCBs with unusual
substrates.
Just as it is possible to buy copper
clad fibreglass panels (blank PCBs), so
too is it possible to buy copped clad
polyimide (DuPont calls this “Kap-
ton”) in sheets, ie, blank flexible PCBs.
The copper clad polyimide some-
times goes by the name “Pyralux”. Pol-
yimide is hardy stuff and can handlethe harsh conditions of an etch bath.
The substrate lends itself well to
the toner transfer resist method, but
we have seen some people comment
that the Pyralux tends to curl when ex-
posed to heat; for example in a heated
etch bath.
The curling may cause the etch re-
sist to lift. We suggest fixing the sheets
to a rigid backing during the etch pro-
cess to prevent this.
This method could also be used
to create custom flexible flat cables
(FFCs).
It’s also possible to buy sheets of
copper foil, in which case there is no
limitation on what substrates are pos-
sible, as long as there is a way to bond
the two together.
We have seen home-made kevlar
PCBs, where the copper is bonded
to the kevlar using fibreglass resin. It
seems the secret here is clamping the
two together rigidly to ensure that the
surface to be etched remains flat.
We’ve even seen PCBs made on glass
using a similar technique, although
soldering onto such a board would be
quite fraught; you would have to do it
carefully to avoid breaking the glass
from differential heating – possibly by
directly heating the glass itself.Conclusion
In this article, we have presented
an assortment of PCB manufacturing
techniques that are accessible to the
hobbyist, but we haven’t been able to
mention every possible variation.
The rise of home CNC type ma-
chines such as mills, laser cutters
and 3D printers is making it possible
to do many things that we would not
have dreamed of previously. Some
techniques are still being developed
and improved, including the tradi-
tional ones.
Having a laser cutter at our disposal
tempts us to try some of the methods
we have mentioned above. However,
we will have to do further research to
ensure we do not damage our machine
or risk our health.
If we needed to make a prototype
board today, we would use the ton-
er transfer or a pre-sensitised photo-
chemical board, followed by a bath
in ferric chloride or ammonium per-
sulphate.
And when we’re in less of a hur-
ry, we order commercial prototype
boards. That is, until someone lends
us a Voltera V-One...It’s not
a PCB but a
PCB pattern cut into
a piece of acrylic which
we produced with our CNC laser
cutter – just to prove it could be done! SC