Apparatus for lead free solder interconnections for integrated circuits

An apparatus comprising:

• a circuit board having a plurality of solder balls disposed on a bottom surface of the circuit board;
• a plurality of conductive traces disposed on a top surface of the circuit board;
• a metal finish disposed over portions of the plurality of conductive traces, wherein the metal finish comprises nickel;
• a flip chip integrated circuit having a plurality of input/output terminals disposed on a bottom surface of the flip chip integrated circuit, wherein the plurality of input/output terminals comprise copper, and wherein each of the input/output terminals has a bottom surface facing the top surface of the circuit board;
• a metal cap layer formed on the bottom surface of each of the input/output terminals, wherein the metal cap layer comprises nickel;
• a plurality of lead free solder connectors disposed between the metal cap layer and the metal finish;
• and
• a first intermetallic compound disposed at an interface between the metal cap layer and the lead free solder connector, wherein the first intermetallic compound is substantially free of copper.

An apparatus comprising:

• an integrated circuit having at least one post extending from the integrated circuit, wherein the post comprises copper;
• a metal cap layer disposed on a surface of the post opposite the integrated circuit, wherein the metal cap layer is not disposed on sidewalls of the post;
• a substrate comprising at least one conductive trace disposed on a first surface of the substrate;
• a metal finish layer overlying at least a portion of the at least one conductive trace;
• a lead free solder connection disposed between the metal cap layer and the metal finish layer, wherein the lead free solder connection has a copper content of less than 0.5 wt. %;
• a first intermetallic compound disposed at an interface between the metal cap layer and the lead free solder connection;
• and
• a second intermetallic compound disposed at an interface between the metal finish layer and the lead free solder connection,
• wherein the first intermetallic compound and the second intermetallic compound are substantially free of copper.