# Guidance on use of vias on power pins of ICs

I have a relatively low power PCB and am wondering if there is ever a need for more than 1 via (0.35mm dia) on any power/ground pins. For example: USB socket for battery charging at max 260mA (5V). SOC with max current consumption of 15mA (3.3V).

Lets do the math.

I'll be making some reasonable assumptions here : standard PCB and DC load.

on 1 oz. copper, the thickness is 35µm, with a 350µm diameter, it gives us a copper cross section of :

$$\\pi\cdot(\frac{350}{2})^2-\pi\cdot(\frac{350}{2}-35)^2=34636\space µm^2\approx0.035mm^2\$$

We know that copper resistivity is $$\ 15\frac{m\Omega\cdot mm^2}{m}\$$

Assuming a standard $$\1.5mm\$$ PCB thickness, it gives us $$\15\cdot\frac{0.0015}{0.035}m\Omega=0.64m\Omega\$$

You will be fine, by a margin and then some.

I Strongly encourage you to do those calculations by hand, it helps build a real understanding that will come in handy when designing more advanced circuits.

• hi just want to clear and validate with saturn pcb : 15*0.0015/0.035 = 0.64mOhm. did you flipp the donominator and enuminator? Commented Jul 9, 2020 at 13:34
• @Hasanalattar you are right, its fixed. Commented Jul 9, 2020 at 13:43
• thanks, I've learned something .. updated mine to match yours .. Commented Jul 9, 2020 at 15:38

no need for extra via ..

i suggest you to play with calculators like Saturn pcb (free software)

the via resistance $$\0.66m\Omega\$$ look at power dissipation @2.5A : 0.00436W * Thermal resistance 90°C/W < 1°C

• Resistance is 0.66mohm, not 66mohm.
– jpa
Commented Jul 9, 2020 at 15:53