siliconchip.com.au Australia’s electronics magazine July 2019 37
files to [email protected]
along with any special requirements
(board thickness, copper thickness,
solder mask colour etc) and they will
e-mail you back a quote.
They will then guide you through
the order process.
On the other hand, as the name
suggests, Guangdong, China-
based PCBCart offers web order-
ing. You can get an instant quote
by visiting http://www.pcbcart.com/quote
and entering your requirements.
Fig.6 shows this page.
We have already filled in the details
of one of our boards, and you can see
that the price (in US dollars) is being
displayed at upper right.
We can then change the board quan-
tity and other requirements and the
price is updated.
The only fields that you need to fill
in are those shown with an orange as-
terisk: the Part Number, Board Type
and Board Size. The other defaults are
fine unless you know you need some-
thing different. You can try changing
some of the parameters and see how
much non-standard features add to the
cost of the basic PCB.
If you increase the quantity, you will
see that the price doesn’t go up all that
much. In our example, five boards cost
US$32.65 ($6.53 each) while 10 boards
cost US$42.20 ($4.22 each) and 100
boards cost $213 ($2.13 each). This is
typical, as there is a fixed cost associ-
ated with every different PCB made;
making more copies of the same board
has a lower incremental cost.
You can vary the board thickness
between 0.4mm and 2.0mm; the cost
varies slightly as you do this. 1.6mm
is a typical thickness and a good de-
fault. 35μm copper is also known as
‘1oz’ and is the default for single or
double-layer boards; 70μm copper is
‘2oz’ and costs a little more.
A green solder mask is usually the
cheapest. In this case, there are other
colours available at the same price (eg,
blue and red) while other options in-
crease the cost slightly. So does opt-
ing for a lead-free or gold finish, or a
shorter lead time.
Note that a 30mil (0.75mm) wide
track on a 35μm (1oz) copper board
can handle 1A with only a 10°C tem-perature rise, so unless you have a spe-
cific high current application, thicker
copper is usually unnecessary.
With the higher cost of 2oz copper,
it’s generally worth using wider tracks
instead, if possible.
Like most online PCB manufactur-
ers, PCBCart accepts payment by PayP-
al, including Visa or Mastercard. They
offer delivery via DHL, UPS or FedEx.
Other companies may offer cheaper
options such as registered post. If you
order from a local manufacturer like
LD Electronics, postage will probably
be quite a bit faster too!Doing it yourself
Of course, if time is of the essence,
then ordering boards from China will
not be your first choice. The age-hon-
oured technique of etching copper
from a pre-laminated board is still
widely used, although modern meth-
ods put some twists on how the etch
resist is applied.
There are also other techniquesFig.7: here’s how the photochemical etch-resist process is used to produce a PCB
(eg, using “Press ‘n’ Peel” film). Both positive and negative processes are shown.RCS Radio’s Ron Bell
and his 31-thou limit
Older SILICON CHIP readers would no
doubt remember the name RCS Radio,
if not its owner, Ron Bell.
If not the first manufacturer, RCS
Radio was certainly a pioneer in this
country, manufacturing “Printed Wiring
Boards” for the military, industry and for
the hobbyist from a factory in Canter-
ubury (boy, were there some arguments
when people started calling them that
American name: printed circuit boards!)
But mostly we remember Ron “do-
ing his nana” when patterns were sent
to him with less than a 31mil track width
or spacing. In fact, he’d get upset at any-
thing under about 40-50mil!
This was long, long before computer
software to produce PCB files. There
weren’t even computers in those days!
PCB patterns were hand-drawn with
pen and ink; later this was superseded
by black crepe tapes and pads.
Often, the patterns were produced at
200% scale, so that when reduced pho-
tographically, minor errors in drafting
were also reduced. They didn’t eliminate
errors in the trackwork itself, though!
After Ron Bell’s passing, RCS Radio
was run by Bob Barnes, until his passing
about ten years ago. By then, many pro-
duction houses around the world were
turning out PCBs which Ron Bell would
have dismissed as “impossible!”