Abstract: A three-dimensional stacked electrical circuit assembly that uses spherical or cylindrical metallic contacts that are surface mounted to input and output pads of circuit substrates that contact recessed wire button contacts disposed in cavities formed in a nonmetallic spacer disposed between the substrates. Each metallic contact fits into a through hole in the spacer and makes contact with a separate wire button contact in the through hole of the spacer. The metallic contacts are recessed within the spacer and are protected from contamination and handling damage. Back-to-back spacers may be employed that use plungers to make contact between wire button contacts disposed therein. The wire button contacts are recessed in the through holes, which provides for an interconnect system having low contact resistance, high current capacity, low contact force, and the ability to customize the shape of the spacer.