US Patent 9024205 Advanced device assembly structures and methods

A microelectronic assembly includes a first substrate having a surface and a first conductive element and a second substrate having a surface and a second conductive element. The assembly further includes an electrically conductive alloy mass joined to the first and second conductive elements. First and second materials of the alloy mass each have a melting point lower than a melting point of the alloy. A concentration of the first material varies in concentration from a relatively higher amount at a location disposed toward the first conductive element to a relatively lower amount toward the second conductive element, and a concentration of the second material varies in concentration from a relatively higher amount at a location disposed toward the second conductive element to a relatively lower amount toward the first conductive element.