When designing a PCB, how to choose the via size? There are two voices.One voice said: choose 10-12mil via,Large vias are not helpful for heat dissipation and flow design, and the parasitic inductance of small holes is very small, which can effectively reduce the impedance of the power path. Another voice said: choose 20~24mil large via, the thick copper thickness with large via,large current carrying capacity and save space.
The copper plating thickness is from 0.8mil to 1.0mil follow IPC Class II and III standard,considering that the copper plating thickness of the vias may be up and down, the middle is narrow, the narrowest limit may be 0.7mil, so we evaluate the thickness of the hole plating in accordance with the 0.7mil.
After setting up the parameters above, we calculate the via current, and summarize the following table:
We have done some analysis on the table above:
- 12mil via can safely carry around 1.2A of current, which is looser than the widely recognized 0.5 in the industry.
- The larger 16mil, 20mil, and even 24mil via do not have obvious advantage in current carrying, and not linearly increasing.
Therefore, we recommend 10~12mil via to load current, higher efficiency, but also more convenient design. Then,If have the current carrying data so can be safely designed? Let’s look at the simulation tests below:
We feel very safe that hitted 20 vias with 12mil on 20A current board,but in fact, the current isn’t as good as you think,they are not evenly distributed over the 20 vias,you can see the case of through-hole current through simple DC simulation.Some vias take the 2.4A current, and some are only 200mA.Of course, the design may not have much risk at last. Because the vias of 12mil are capable of carrying more than 2A of electric current at 30 degrees of temperature.But what if the inhomogeneity is further magnified? This is related to the passage of your current, the distribution and number of vias. What if one of the vias has gone through the 3A or even 4A current? At this point, you design 25 or 30 vias,it’s not great helpful if there isn’t critical position current, the reason is the same sentence: “the current is not as good as you think.”
This conclusion is also true when determining the width of copper area,we can find it from a lot of simulation results, when the large current design is not enough in one layer of copper area, a layer is added to take the current, and the current is not equally distributed.
When the current reaches magnitude 20A or greater, the conventional copper current carrying capacity and through hole current carrying capacity are both at risk. The most effective way is to evaluate it through DC simulation software.
Simulation of the DC voltage drop the algorithm is not complex, setting is simple, the simulation result is more accurate, it’s large helpful for the design of large current, it’s PCB design engineer or hardware engineers’s necessary entry tool in the beginning of simulation touch.
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