Hi I'm Alex and welcome to Super Make Something Basics. Today we take a look at how to properly
size traces on your custom circuit boards.
This episode is sponsored by PCBWay. Follow the link in the video description below to
order custom circuit boards for your projects at PCBWay.com
I'm currently working on creating an open-source actuator to make it easier for people to get
started with robotics. Like with my previous DIY Stream Deck project, my goal is to make
the actuator as easy as possible for others to build for themselves, so I'm again designing
a custom printed circuit board or PCB that will allow anyone to replicate the electronics
portion of this build even if they only have basic soldering skills.
Designing and laying out circuit boards is one of my favorite parts of DIY electronics
projects. Fitting all of the circuit connections onto a tiny board and routing the wire traces
to make sure that everything is connected correctly is like a miniature puzzle, and
is not only super satisfying when everything works as intendended, but also creates a really
cool looking graphic when the board is fully laid out. After I finished my initial actuator
circuit board layout, I therefore took a screenshot of my PCB design software and excitedly posted
it online, where I received the following surprisingly consistent feedback.
NOT TODAY! HA! HA! HA!
My circuit board traces were too thin. While the internet often has vastly differing opinions
on basically everything, the consistency of these comments made me wonder "how do you
properly size circuit board traces?" So, with some basic electronics components, circuit
boards from PCBWay, and a thermal imaging camera from Banggood.com, I set off to learn
how to correctly size my circuit board traces to make sure that this and future boards were
as well designed as possible.
As with most things in our Universe, the answer to "why does it matter how wide your circuit
traces are?" is heat. Circuit boards essentially exist to carry electricity from one electronics
component to another. As electricity, or more precisely current, travels along the various
traces on a board, heat is generated due to a process known as "Joule Heating." Traces
on a PCB are typically made of copper. As electrons move through a trace, they bump
into copper ions in their path, transferring some of their energy, and causing the copper
ions to vibrate. This vibration causes the PCB trace to warm up over time.
The idea behind correctly sizing a circuit board trace is to make sure that this heat
can be transferred to the environment quickly enough before the trace gets too hot and the
circuit board fails. While maximum temperature before the fiberglass layer on a typical PCB
begins to soften is around 130 degrees Celsius, which is known as the glass transition temperature,
it's usually a good idea to keep the temperature well below this limit both for component and
user safety.
So how do you actually size a PCB trace? The answer to this question can be found in the
"IPC-2221," a 130 page technical document that covers nearly every aspect of printed
circuit board desig. Charts that relate current, cross-sectional area, and temperature rise
for internal and external traces can be found in Figure 6-4. From these charts, it is possible
to create the following equation using regression, which can then be used to calculate trace
width by knowing the density of copper used by the circuit board manufacturer during the
PCB fabrication process.
In my board design, I knew that the copper density would be 1 oz/square foot, that the
maximum current through my biggest trace would be around 2 Amps, and that I wanted a maximum
temperature increase of 10 degrees Celsius. Since this would be a relatively simple breakout
board, I also knew that my PCB would only have two layers, meaning that all of the traces
would be external, which allowed me to select the appropriate curve coefficients. From this,
I was able to calculate that the required trace width for this portion of the board
would be 30 mils.
But exactly how accurate are trace width values reported by these design curves?
Armed with this new information, I opened up "Altium Designer," which I used to design
the original version of the actuator board, and changed the width of the traces that would
supply power to the board and motors to 30 mils. A quick thank you to Altium for providing
the "Altium Designer" software for me in order to make PCB designs for my videos. If you
are interested in trying Altium Designer out for yourself, simply follow the link in the
video description below for a free 30 day trial.
After I had exported the PCB fabrication files, I next headed to PCBWay.com, who graciously
sponsored this video. On the site, I uploaded a zip file of all of my fabrication files,
selected the appropriate manufacturing options to match the settings I had used in my trace
width calculations, and submitted the order. Less than a week later, the boards arrived
at my door, and like always, they were absolutely perfect. Over the last year, I've exclusively
had boards for all of my electronics projects manufactured through PCBWay and have always
been pleased with the results. In case you are looking for a circuit board manufacturer
for your next project, consider checking out PCBWay. Their speed, price, and quality can't
be beat!
With the boards in hand, it was time to test the accuracy of the IPC-2221 design curves.
To avoid risk to my actuator components and control the amount of current accurately,
I used a set of resistors to simulate the maximum electrical load of my motors, whose
value I calculated using an expression for Ohm's Law. When fully built, I knew that the
circuit would be powered with a 12 Volt power supply. To get 2 Amps to run through the trace,
which is the maximum current that can be supplied by the motor driver, I would therefore need
a 6 Ohm resistor. However, a variation of Joule's first law states that the power dissipated
through a load is equal to the current times the voltage, meaning that I would need a resistor
that could dissipate at least 24 Watts to make sure that it wouldn't burn up during
testing. As such, the 1/4 watt resistor commonly found in standard electronics kits wouldn't
do, so I headed online and picked up a shiny 6 Ohm, 50 Watt power resistor, which would
be more than capable to survive this experiement.
After soldering the resistor and some wire to one of the board's 30 mil traces, I connected
everything to a benchtop power supply. The temperature increase of the trace was measured
with an HTI Thermal Imaging camera, which was sent to me by Banggood.com for these tests.
After mounting the camera onto a tripod using its 1/4-20 screw interface, I first measured
the ambient temperature of the board. Next, I turned on the power supply, set its output
to 12 Volts, and began monitoring the temperature increase of the PCB region that contained
the wired trace. One thing to note is that the traces on the PCB also have a slight internal
resistance that is a function of their length. As such, I needed to increase the output voltage
of my power supply in order to get 2 Amps to flow through the circuit. After approximately
ten minutes the board had reached steady state temperature and I recorded a final reading
of 25.1 degrees Celsius, a temperature increase of 6.3 degrees.
So what exactly does this result mean? Overall, the measured temperature rise in the trace
was less than the temperature rise predicted by the equations derived from the IPC-2221
design curves. This means that the traces were adequately sized to handle the amount
of current to stay beneath the desired 10 degree Celsius temperature increase and is
great news for the open source actuator project, because the PCBs should be able to stay cool
even under the worst-case operating conditions.
However, the difference between the predicted 10 degree and measured 6.3 degree Celsius
increase is not trivial, so it's equally important to understand why this discrepancy may exist.
First, the IPC-2221 design curves incorporate a 10% derating factor to allow for variations
during PCB manufacturing, which creates a bit of a safety margin in case the copper
density of a trace is a bit lower or the trace width ends up being a bit narrower than intended
when a PCB is manufactured. Next, there is likely also a bit of measurement error between
the actual temperature and measured temperature reported by the thermal camera. While I was
not able to verify the thermal camera's absolute accuracy, I did sanity check the camera's
reported values by measuring the temperature of one of my 3D printer's heated beds. During
these tests, I found that there was about a 0.8 degree difference between the value
reported by the camera and the printer, which is in line with the "+/- 2% or +/- 2 degree
Celsius" temperature measurement accuracy of the camera. The value reported by the printer
is likely also not perfect, but this could leave only around 0.8 degrees of unaccounted
for temperature from things like uncharacterized convective cooling effects, uncertainty in
the voltage and current reported by my power supply, and from PCBWay actually using slightly
more copper in the traces than indicated in their online ordering form to add a bit of
extra safety margin.
With all of this being said, it is always important to do your own validation experiments
when making circuit boards that have to adhere to tight performance specifications for your
own application. However these results suggest that the width of the motor traces in the
open source actuator PCB are adequately sized and that the IPC-2221 guidelines for trace
width provide a conservative estimate for two-sided circuit boards manufactured by PCBWay
that, from a thermal standpoint, will allow your circuit boards to perform safely in your
projects.
Based on this limited testing, the IPC-2221 specs seem to provide good rules of thumb
for properly sizing your circuit board traces. A big thank you to PCBWay for supplying boards
for this experiment and to Banggood.com for providing a thermal imaging camera for this
video. The camera seems to provide accurate temperature measurements, and I can see it
being an extremely handy tool for both electronics troubleshooting and 3D printer benchmarking.
Please check out the links in the video description below if you are looking to have some PCBs
made for your next project or are interested in picking up the thermal imaging camera for
your toolbox!
Having validated that the boards will be able to handle the motor current, it's now time
to start designing mechanical components for the open-source actuator. If you would like
to support that build or found this video useful, please consider giving this video
a like, subscribing to my channel and becoming a Patron on Patreon or a member on YouTube!
Your support helps me make more of these videos and ensures that my content will always be
free to help others learn more about 3D printing, electronics, and other topics covered on this
channel.
Well, that's all there is to this episode! Thanks for watching, now "Go Super Make Something!"