2
\$\begingroup\$

Eventually I see power traces on both sides of dual layer PCBs that have lots of massive vias, do the vias help the traces handle more power? Does it increase heat dissipation and/or decrease resistance?

I sometimes see them in PCBs with the same trace on both sides, so the via's function apparently is not to carry current from one side to another.. is it adding thermal mass or..?

Is there a rule of thumb/graphs/calculations/application notes for this? Or is it more empirical/case specific?

Info about vias for PCB heatsink pads for power ICs is quite common but I couldnt find much about traces.

enter image description here

I know there are other methods of increasing power handling and heat dissipation for traces, but I'm specifically curious about this method. I think I'm not referring to PCB stitching of RF planes.

\$\endgroup\$
2
  • 1
    \$\begingroup\$ Is there a big power-hungry chip on the other side of the board, above the square-ish end of the region with the holes? \$\endgroup\$
    – The Photon
    Commented Oct 8, 2015 at 23:18
  • 1
    \$\begingroup\$ In this case yes, but I've seen it on PCB antennas and other cases (PSUs) as well. I just couldnt find better example pics. \$\endgroup\$
    – Wesley Lee
    Commented Oct 8, 2015 at 23:23

3 Answers 3

5
\$\begingroup\$

Well if you have a very thick trace to carry a lot if current on one side and you want to flip to the other you often use a bunch of vias. Vias have their own current carrying capacity per thermal rise just like traces do.

So what often happens is an engineer has to do this so instead of calculating how many vias they need they just add more than they think they would possibly need just to be covered (since normal such vias are very cheap). Each via in parallel is like a wire in parallel the current will be split (more or less) between them. In some case such as very fast switching of high currents the location of the vias might matter, so the split might be a little different in that specialized case.

Here's a link to a pcb via calculator that includes current carrying that might be instructive.

\$\endgroup\$
2
\$\begingroup\$

This technique is generally known as "via stitching".

The vias in your picture are most likely being used to conduct heat away from a part on the other side of the board. (Given all of the decoupling capacitors, I'd guess it's some sort of high-speed digital part.) The heat capacity of a single via is relatively low, so many vias must be used to efficiently conduct heat away from the part on the opposite side.

In a comment, you mentioned having seen vias used around PCB antennas. This is a different use case; in this case, they are being used to create a shield around RF circuits, either to isolate them from external signals, and/or to prevent them from radiating signal into other parts of the board.

\$\endgroup\$
1
\$\begingroup\$

stitching vias are used for multiple purposes.

  1. Increased current capability of traces
  2. Increased reliability of trace (in case of single via failure)
  3. Thermal conduction to enable removal of heat to other layers
  4. ground plane stitching. If you have multiple layers on a PCB and with more than one ground plane you will typically want these connected with a very impedance. Using multiple stitching vias is one way to achieve this. It can also used on edges of boards to provide limited shielding to sensitive/high speed traces on inside layers.
\$\endgroup\$
1
  • \$\begingroup\$ Maybe this sentence could be improved? " IF you have multiple layers on a PCB and with more than one ground plane you want these to a very impedance connecting..." I think I understand but it isn't clear. I'm not confident I can rewrite the way you'd like it. \$\endgroup\$
    – gbulmer
    Commented Oct 9, 2015 at 0:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.