I am designing a PCB in EAGLE. In this PCB, the major heat sources are my SMD/SMT resistors.
I learned that a general principle to dissipate heat from PCB components, is to place thermal vias directly at the bottom of high-power components ( reference: https://www.pcbcart.com/article/content/pcb-theraml-design.html ).
However, I noticed that the EAGLE footprint of all of my SMT/SMD resistors, which I downloaded from Ultra Librarian (https://www.ultralibrarian.com/), come with a "tRestrict" layer at the center, in between the two pads. As an example, the photo below shows a ERJ-UP3F2201V (Panasonic) resistor on my board; all of the resistors on my board (all are from Panasonic; all of their EAGLE footprints were downloaded from Ultra Librarian) share this pattern of footprint.
"tRestrict" is a layer that indicates areas where copper will not be poured. (https://www.autodesk.com/products/eagle/blog/every-layer-explained-autodesk-eagle/).
My questions are the following:
(1) What is the purpose(s) for having a tRestrict layer below a SMT/SMD resistor? I am new to PCB design, and I assume that it would be ideal to dissipate heat from major heat-generating components, such as a resistor. However, the lack of a copper plane below the resistor appears to be against this intuition.
(2) If (1) is indeed justified, i.e. it is important / necessary to omit the copper layer below the SMD/SMT resistors, would it still be useful to install thermal vias below the resistor (i.e., inside the tRestrict region)? Without the heat-conducting copper, I do not see how these would help by much, but thought that I would still ask!