Circled in red are component through holes in a copper pour plane that are missing areas / don't have the copper poured completely around the via. Seen on tons of components both through hole and surface mount.

Why does the circled in red feature exist?

What is the feature called?

When should a designer add it to their designs?

When shouldn't they add it?

Does it matter whether the component is through hole or surface mount to add this feature?

How do you make this feature in altium?

enter image description here

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    \$\begingroup\$ What Chester Gillon says sounds right but double check that's the copper layer; not to imply that I've seen every implementation of thermal reliefs, but I've never seen that implementation, with square-profile nibbles taken out rather than the "border + spoke" way of doing it. \$\endgroup\$
    – vir
    Oct 4, 2023 at 22:14

2 Answers 2


They looks to be Thermal Relief pads to aid in manufacturability.

From some searches:

  1. Thermal Relief Design Guide for Your PCB for Altium
  2. PCB Thermal Relief Guidelines for Effective Layouts for Cadance

Relevant part from the Altium article:

A thermal relief pad provides a way to keep heat confined to a pad for mounting a component to a printed circuit board with solder. The pad for a component normally peaks through the solder mask, allowing solder to be placed on the pad during assembly. Some copper is removed from the edge of a thermal relief pad, allowing heat to be confined in the pad when applying solder during assembly.

Edit: In response to the comment, I have no direct experience of calculating the effect of Thermal Relief pads on the current carrying capability of the component or increase parasitic inductance, but found the following:

  1. Thermal Relief Via Design for Proper Impedance from Altium
  2. Does adding thermal relief on PCB increase electrical resistance? answer on stackexchange
  • \$\begingroup\$ does this effect the current carrying capability of the component or increase parasitic inductance? \$\endgroup\$
    – user298907
    Oct 5, 2023 at 16:59
  • \$\begingroup\$ @Erv have edited the answer with some more links \$\endgroup\$ Oct 5, 2023 at 17:18

Looks like an unusual implementation of thermal reliefs.

These are usually required in through hole soldering processes to prevent heat from being sucked away from the hole by surrounding copper structures. If the heat is kept within the hole, you'll achieve better solder melting/flow and thus a better hole fill which results in a more reliable solder joint.

In surface mount soldering processes on the other hand thermal reliefs are usually optional, because the whole board is heated up anyway. However, often times thermal reliefs are used with surface mount as well to make manual rework easier.


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