Electronic element mounting substrate, electronic device, and electronic module for improving and obtaining long-term reliability

A heat dissipating substrate comprising:

• a substrate in a quadrangular shape, comprising a first main surface and a second main surface opposite to the first main surface;
• and
• heat dissipators arrayed along a first direction and embedded in the substrate, made of a carbon material in which six-membered rings are connected by a covalent bond and each of a plurality of surfaces are bonded by van der Waals forces, and the plurality of surfaces of the heat dissipators comprising a third main surface located on the first main surface side in a thickness direction and a fourth main surface opposite to the third main surface, wherein
• the heat dissipators have a first heat dissipator and a second heat dissipator,
• both of the first heat dissipator and the second heat dissipator have anisotropy of thermal conductivity,
• the thickness direction is a second direction,
• the thermal conductivity of the first heat dissipator in the first direction is higher than either the thermal conductivity of the first heat dissipator in the second direction or the thermal conductivity of the second heat dissipator in the second direction,
• the thermal conductivity of the first heat dissipator in the second direction is lower than either the thermal conductivity of the first heat dissipator in the first direction or the thermal conductivity of the second heat dissipator in the first direction,
• in the first direction, the thermal conductivity of the substrate is lower than the thermal conductivity of the first heat dissipator,
• in the second direction, the thermal conductivity of the substrate is higher than the thermal conductivity of the first heat dissipator.