Interposer and substrate module

An interposer to couple together a first substrate and a second substrate, the first substrate including a first-substrate upper main surface and a first-substrate lower main surface and including a first electrode that is a portion of the first-substrate lower main surface, the second substrate including a second-substrate upper main surface and a second-substrate lower main surface and including a second electrode that is a portion of the second-substrate upper main surface, the interposer comprising:

• a resin layer including a resin-layer upper main surface to be joined to the first-substrate lower main surface and a resin-layer lower main surface to be joined to the second-substrate upper main surface;
• and
• a plurality of metal bodies in the resin layer and separated from each other, a dimension of each of the plurality of metal bodies in an upward-downward direction being greater than a dimension of each of the plurality of metal bodies in a direction orthogonal to the upward-downward direction;
• wherein
• at least one of the plurality of metal bodies is located in the first electrode and at least one of the plurality of metal bodies is located in the second electrode to electrically couple together the first electrode and the second electrode.