siliconchip.com.au Australia’s electronics magazine July 2019 35
If you have a ‘zipped’ set of Ger-
bers, you will need to extract the in-
dividual files before opening them in
gerbv. Multiple layers can be opened
from the File → Open Layer dialog
box. You can change layer colours,
rearrange and hide individual layers
with the panel at left.
When exporting to PDF (File → Ex-
port → PDF), you can select one layer
at a time by clearing all but one of the
checkboxes in the layer tab. Change
the layer colour to black by pressing
F6 and picking the colour from the
popup menu, if you plan to print the
PDF as an optical mask.
You may need to set the background
colour to make the layer visible; this
can be done via View → Change back-
ground colour.
Fig.2 shows gerbv displaying the
Gerber files for our recent (April
2019) iCEstick VGA Adaptor PCB
(siliconchip.com.au/Article/11525).
The colours shown are assigned es-
sentially randomly when you open up
the layers and are designed to make
each layer distinctive. You can change
them to more realistic colours if you
want (eg, green for copper, light grey
for solder mask openings etc).
Getting PCBs made
from Gerber files
The first technique for making PCBs
is the one we use most at SILICON CHIP.
It sounds really easy, too – we get
someone else to do it!
In spite of what you might think,
it’s not expensive, and the results are
very good.
Of course, the proviso is that you
won’t get the PCBs right away unless
you pay a lot for “fast turnaround”
and express delivery. It typically takes
a week or two between ordering the
PCBs and receiving them, sometimes
longer.
So if you need a prototype today,
you should probably look at one of
the other options.
For smaller orders (eg, less than 100
units), the cost of manufacturing PCBs
is normally kept reasonable by aggre-
gating boards from many customers.
One minor side effect of this is that
a small tracking code may be added
to the silkscreen of your board, so that
the manufacturer knows which board
goes to whom.
An example of this is shown in
Fig.3. It’s usually quite small and
placed in an out-of-the-way location.
Some manufacturers have web-
based ordering while others accept
files via e-mail and will send you a
quote (usually within one business
day). Ordering via e-mail can be con-
venient because this makes it easy
for them to point out any problems
they may find with your files so you
can correct them before manufactur-
ing begins.
Minimum quantities are usually in
the order of 5-10, with a decreasing
per-board cost as you order more. For
prototypes, you’ll generally want to
order a small quantity, but it’s good
to have a couple of spares in case you
make a mistake during assembly, or
find it necessary to modify the board.Design rules
If you’ve just started out using anEDA tool like CircuitMaker, Eagle,
KiCad or DipTrace, you may not be
familiar with design rules. They are
an important part of PCB manufac-
turing since they aim to ensure that
the design does not incorporate any
elements which can not be easily and
reliably made.
Board manufacturers generally sup-
ply a set of design rules which, if ad-
hered to, guarantee that your design
can be manufactured using their pro-
cesses and equipment, with a mini-
mal chance of failures. You can add
your own, stricter design rules to en-
sure the safety of your design (such
as ensuring separation between high-
voltage tracks).
For example, you can see PCBCart’s
rules at http://www.pcbcart.com/pcb-fab/
standard-pcb.html, partially repro-
duced in Fig.4.
In some cases, you can violate someFig.4: PCBcart’s specifications and
requirements. You will need to
make sure your design adheres
to these rules shown here, or they
will complain when you send them
your files. Luckily, all the rules can
be programmed into the Design
Rule Check settings of most ECAD
software, and the software will then
automatically inform you of any
problems (or may not even allow you
to create them in the first place!).Photomicrograph of a section through a multi-layer PCB complete with an IC
soldered to the top layer. The copper section at right is a via which connects
two of the internal layers.