Intermediate substrate

An intermediate substrate comprising:

• a substrate core, having first and second principal surface sides, comprised of a plate-form main core body made of a polymeric material, and including a sub-core compartment formed therein so as to decrease the thickness thereof relative to a first planar principal surface, and a plate-form sub-core section made of a material having a coefficient of linear expansion smaller than the core main body formed in a plate, said sub-core section being accommodated in the sub-core compartment and having a thickness matching the overall thickness of said main core body,
• a first terminal array comprised of a first side, first type terminal and a first side, second type terminal formed at the first principal surface side of the substrate core, and functioning, respectively, as a power source terminal and a ground terminal, and of a first side signal terminal, and
• a second terminal array comprised of a second side, first type terminal and a second side, second type terminal formed at the second principal surface side of the substrate core, and conductively connected to, respectively, the first side, first type terminal and the first side, second type terminal, and of a second side signal terminal conductively connected to the first side signal terminal,
• the first terminal array being disposed in a relative position that is entirely included in a projected region of the sub-core section geometrically projected orthogonally onto a reference plane parallel to the planar principal surface of the substrate core.