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I'm designing a 4 layers PCB in Altium Designer 19.1. My PCB have a ground plane on layer 2 and a small copper pour area on layer 1. The copper pour area on layer 1 is connected to the ground plane using vias. Currently those vias have thermal relief on layer 1 and 2 but I would like to change the polygon connect style of those vias to direct connect. I have other vias, outside the small copper pour area of layer 1, that connect to the ground plane on layer 2. I would like the polygon connect style of those vias to remain unchanged. How could I do that? Would creating a new polygon connect style rule with the query TouchesRoom('Name Polygon Layer 1') work? I suppose it won't since polygons and rooms are two different things.

Thanks!

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  • \$\begingroup\$ May I ask why you are using thermal reliefs on vias at all? Unless you're soldering to them, there is absolutely no reason to give them thermal reliefs \$\endgroup\$ – DerStrom8 Oct 10 '19 at 1:52
  • \$\begingroup\$ @DerStrom8 Well, I've never asked myself why, I've always done it. I guess it can be harder to solder pads that are connected to vias with low thermal resistance (no thermal relief) to big copper plane. Since I will use a oven to solder my boards it doesn't really matter. Does it? \$\endgroup\$ – A.Lacasse Oct 10 '19 at 2:09
  • \$\begingroup\$ Thermal reliefs should be used on component pads, but there is never a situation that I have ever faced in which a via needs to have thermal reliefs. The only thing I can think of is if you plan to use a via as a solder pad/test point, but usually you use standard through-hole pads for that purpose. You absolutely need to be concerned with balancing the thermal mass on each of the component pads because in reflow processes, if the balance is wrong then two-pin components such as capacitors and resistors might tombstone. Again though, use thermal reliefs on the component pads, not the vias. \$\endgroup\$ – DerStrom8 Oct 10 '19 at 2:51
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Summing up what I mentioned in the comments-

999 times out of 1000 you don't need to have thermal reliefs on vias. The only case where you might want to do this is on a prototype board where you expect to need to solder a wire into the via barrel, either to use it as a jumper or as a test point. Usually however, you would want to use a standard through-hole pad for this or, if you have the space, a dedicated test point component.

Thermal reliefs are required on SMD component pads to improve manufacturability by preventing a mismatch in thermal mass between component pads. This can especially be an issue on two-pad components such as SMD resistors and capacitors. If one pad has more thermal mass than the other, it will take longer to heat up and for the solder paste to flow. The paste on the other pad will almost certainly melt first, and the surface tension of the solder will cause the opposite end of the component to flip up. This leads to an effect referred to as "tombstoning", in which the component literally stands up on end. In designs that require hand-soldering, thermal reliefs are used to ease the soldering process as it reduces the dwell time necessary for the iron to heat up the joint and melt the solder, speeding up the entire process and ensuring the joint is solid and consistent throughout the barrel.

In your case it is probably safe to just make all of your vias a direct connect to the polygon pours (and internal planes, if you've got them).

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  • \$\begingroup\$ Thank you for your answer :) \$\endgroup\$ – A.Lacasse Oct 10 '19 at 3:11

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