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I am trying to understand what size vias I should use for my 5V power traces. The trace typical runs at 0.5-3 amps and is 2mm and about 150mm in length. The width is huge, but I do have the extra space and I'd like to have as little resistance as possible since I am using a battery. The power traces only navigate the external layer of the PCB, no inner layers with poor heat transfer used.

But my design software's default via is 0.8 diameter and 0.4 via drill. Should I expect a voltage drop across the via. How will the resistance of this size via compare to my trace's resistance?

Edit: this is a 4 layer PCB, with 1 oz copper weight. Here is a link to my PCB board manufacture's capabilities: capabilities

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  • \$\begingroup\$ There is a via resistance calculator available which may give a direction. Note the answers to this question where you can find some measured values for the resistance of vias. Theory and practice show the same direction but also vary by some amount. If you have room for it, estimate the number of vias and add a few more to gain some margin - plating thickness in vias has some variation over batches ;-) \$\endgroup\$
    – datenheim
    Jan 2 at 19:35

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The plating thickness of a via is typically circa 20µm, or roughly equivalent to 0.5oz copper.

Given the via is a cylinder, the width of a via can essentially be considered as the circumference of the drill diameter, so: \$\pi\times d\$.

We can calculate then that, a 0.4mm via drill will be roughly equivalent to a 1.25mm PCB trace on 0.5oz copper, or for 1oz copper equivalent, half that (0.63mm).

For your 2mm wide trace, assuming 1oz copper, four 0.4mm vias would have a roughly equivalent current handling capacity. Alternatively you could use a single via with 1.27mm hole diameter.

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  • \$\begingroup\$ Those are reasonable assumptions but before making design decisions the PCB vendor should be consulted to be sure this is in line with their processing. \$\endgroup\$
    – jwh20
    Apr 15, 2021 at 14:00
  • \$\begingroup\$ what does the 0.8 in the 0.8/0.4 via spec mean? If the drill diameter is 0.4 then why does the 0.8 matter? For the suggested 1.27mm via drill would 1.5/1.27 be acceptable? \$\endgroup\$
    – Feynman137
    Apr 15, 2021 at 16:50
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    \$\begingroup\$ The 0.8 is the copper annulus size. It shouldn't matter too much, particularly if your trace is wider anyway. \$\endgroup\$
    – Tom Carpenter
    Apr 15, 2021 at 17:19
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    \$\begingroup\$ Good answer. Let me add there is a calculator available. I found it interesting that the copper in vias seems to have a slightly lower conductance (1.9 µOhm-cm) than in bulk (1.77 µOhm-cm). \$\endgroup\$
    – datenheim
    Jan 2 at 19:45

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