# Trace width & vias for PCB carrying 15vdc/1a

I am designing a PCB which includes a 3.3v circuit w/ a microcontroller than controls (via a relay) a higher voltage (max 15vdc, 1a) circuit. Is it OK to run that amount of current and amps on PCB traces/vias? Will I need to increase the width of the traces or something?

As a sidenote, I am new to PCB design and using Eagle. My trace with is listed as "0.016" without units - I assume this means 16mil?

You are correct, the widths are listed in inches so "0.016" means "0.016 inches", or 16 mil.

IPC-2221 generally governs trace widths for given currents. There are numerous calculators that can be found online that will tell you what your trace widths need to be based on IPC standards. Here is one of them, from Advanced Circuits:

http://www.4pcb.com/trace-width-calculator.html

You don't mention your copper weight or allowed temperature rise, so it is very difficult for us to be able to tell you if your width will be enough.

As for vias, I would use the calculator to determine the trace width, and use that width as the hole diameter for the via. I would then make the pad diameter twice the hole diameter, and I would use one via for every 1/2 amp, so 2 vias in your case, for every trace connection/termination.

• Ok, thanks. That calculator mentions internal and external traces. What does that mean? My understanding was that traces were always 'external' (on the top of bottom of the PCB). Commented Apr 5, 2017 at 14:47
• Also - it asks for input thickness... what does this refer to? The wire I will be plugging into the screw terminals for the higher voltage circuit? Commented Apr 5, 2017 at 14:48
• Many PCBs have 4 or more layers, basically made by laminating thin two layer boards together. Inner layers can carry less current for the same size track because they aren't exposed to air for cooling.
– Evan
Commented Apr 5, 2017 at 14:48
• Internal traces are traces that are on internal layers. External traces are on either the top layer or on the bottom layer. "Thickness" is the copper layer weight (0.5 oz/sq. ft, 1 oz/sq. ft, etc). Commented Apr 5, 2017 at 14:51
• Thickness is the copper foil used to make the PCB. 1 oz/ft^2 is somewhat standard, but 2 oz is common for high current, and 0.5 oz/ft^2 or .33 oz/ft^2 is common for high density signals because it is easier to etch into very narrow lines.
– Evan
Commented Apr 5, 2017 at 14:51

Yes, 15 VDC @ 1 A is perfectly fine over PCB traces. Just make sure to adequately size the vias/traces; there are a multitude of via/trace calculators (the size will be determined by the current capacity required, not the voltage).

Also, the amount of current that a trace can carry is limited determined by your stackup, so you will want to determine that (or worst-case for something like 1/2 oz copper).