Interconnections for flip-chip using lead-free solders and having improved reaction barrier layers

An interconnection structure suitable for flip-chip attachment of microelectronic device chips to packages, comprising:

• a two-layer ball-limiting metallurgy comprising an adhesion layer, wherein the adhesion layer serves to promote the adhesion of BLM to the substrate, and a solder reaction barrier/wettable layer, said reaction barrier/wettable layer serving to facilitate both solder wettability and slow solder reaction, the layer being for placement between a microelectronic device and said solder, and wherein said solder reaction barrier/wettable layer is of a metal readily reactive with components of a tin-containing lead-free solder, so that said solder reaction barrier/wettable layer is only partially consumed during soldering, wherein residual unreacted reaction barrier/wettable layer still remains after being placed in contact with said lead free solder during soldering;
• and
• one or more lead-free solder balls selectively situated on said solder wettable layer, said lead-free solder balls comprising tin as a predominant component and one or more alloying components.

An interconnection structure suitable for flip-chip attachment of microelectronic device chips to packages, comprising:

• a three-layer ball-limiting composition comprising an adhesion layer, a reaction barrier layer on top of said adhesion layer and a solder wettable layer, wherein said adhesion/barrier layer is between a microelectronic device and said solder wettable layer and wherein said solder wettable layer is of a composition sufficiently reactive with components of a tin-containing lead free solder, and the reaction barrier layer is substantially less-reactive with solder after being placed in contact therewith in a solder joining process;
• and
• one or more lead-free solder balls selectively situated on said solder wettable layer, said lead-free solder balls having tin as a predominant component and one or more alloying components selected from the group consisting of Cu, Ag, Bi, Co, La, Fe, Ni and Sb, whereby said lead-free solder ball substantially avoids alpha particle emission and induced soft logic errors which result therefrom.