Multilayer substrate, interposer, and electronic device

An interposer disposed between a first element and a second element and electrically connecting the first element and the second element, the interposer comprising:

• a base body including:
• a plurality of insulating base material layers stacked on one another;
• and
• a first main surface and a second main surface perpendicular or substantially perpendicular to a stacking direction in which the plurality of insulating base material layers are stacked, the first main surface and the second main surface facing each other;
• a plurality of first external electrodes on the first main surface and made of metal foils;
• a second external electrode on the second main surface and made of metal foil;
• a plurality of first interlayer connection conductors connected to the plurality of first external electrodes and disposed in the base body;
• at least one second interlayer connection conductor disposed in the base body;
• and
• at least one third interlayer connection conductor disposed in the base body;
• wherein
• the interposer further includes a first interlayer connection portion connected to at least one metal foil of one of the plurality of first external electrodes and a second interlayer connection portion connected to at least another metal foil of the plurality of first external electrodes;
• the first interlayer connection portion is provided by at least one of the plurality of first interlayer connection conductors, the at least one second interlayer connection conductor, and the at least one third interlayer connection conductor;
• the second interlayer connection portion is provided by at least another one of the plurality of first interlayer connection conductors, or by at least another one of the plurality of first interlayer connection conductors and another third interlayer connection conductor;
• and
• the at least one second interlayer connection conductor has higher conductivity than the plurality of first interlayer connection conductors and the at least one third interlayer connection conductors.

An electronic device comprising:

• a first element;
• a second element;
• and
• an interposer disposed between the first element and the second element and electrically connecting the first element and the second element, the interposer including:
• a base body including:
• a plurality of insulating base material layers stacked on one another;
• and
• a first main surface and a second main surface perpendicular or substantially perpendicular to a stacking direction in which the plurality of insulating base material layers are stacked, the first main surface and the second main surface facing each other;
• a plurality of first external electrodes provided on the first main surface and made of metal foils;
• a second external electrode provided on the second main surface and made of metal foil;
• a plurality of first interlayer connection conductors connected to the plurality of first external electrodes and disposed in the base body;
• at least one second interlayer connection conductor disposed in the base body;
• and
• at least one third interlayer connection conductor disposed in the base body;
• wherein
• the interposer further includes a first interlayer connection portion connected to at least one metal foil of one of the plurality of first external electrodes and a second interlayer connection portion connected to at least another metal foil of the plurality of first external electrodes;
• the first interlayer connection portion is provided by at least one of the plurality of first interlayer connection conductors, the at least one second interlayer connection conductor, and the at least one third interlayer connection conductor;
• the second interlayer connection portion is provided by at least another one of the plurality of first interlayer connection conductors, or by at least another one of the plurality of first interlayer connection conductors and another third interlayer connection conductor;
• and
• the at least one second interlayer connection conductor has higher conductivity than the plurality of first interlayer connection conductors and the at least one third interlayer connection conductor.