Single-grain Sn-rich micro-bump by reducing Sn undercooling with heterogeneous nucleation.

[Display omitted] • Sn heterogeneous nucleation on (Pd,Ni)Sn 4 compound greatly reduces Sn undercooling. • Sn undercooling reduction attributes to single-grain formed in micro-bump. • Single-grain restricts electromigration and consumption of electroless-Ni. • Ni 3 P formed at solder/Ni(P) interface degrades EM lifetime. The heterogeneous nucleation on the limited (Pd,Ni)Sn 4 compound observed at the solder/Pd/Ni(P) interface greatly reduces the Sn undercooling. The undercooling reduction of Sn is the key resulting a single-grain structure for the Sn-rich Sn1.5Ag0.1Cu micro-bumps. Without (Pd,Ni)Sn 4 compound formed at the solder/Pd/Ni(P) interface, the Sn-rich Sn1.5Ag0.1Cu micro-bumps has a polycrystalline grain structure. Compared to the solder matrix with poly-grains structure, the single-grain solder matrix restricts electromigration atomic flux and the consumption of the Ni(P) layer, which mitigates EM effect and prolongs EM life time of the micro-bumps. Ni 3 P layer formed at the solder/Pd/Ni(P) interface greatly influence EM behavior and lifetime. [ABSTRACT FROM AUTHOR]