Influence of SrTiO3 nano-particles on the microstructure and shear strength of Sn-Ag-Cu solder on Au/Ni metallized Cu pads

Nano-sized, nonreacting, noncoarsening SrTiO₃ particles have been incorporated into Sn-3.0 wt% Ag-0.5 wt% Cu solder alloys and the interfacial microstructure and the shear strength on Au/Ni metallized Cu pads ball grid array substrates investigated as a function of the number of reflow cycles and aging time. At their interfaces, a scallop-shaped ternary Sn-Ni-Cu intermetallic compound layer was found in both plain Sn-Ag-Cu solder joints and solder joints containing SrTiO₃ nano-particles, and the intermetallic compound layer thickness increased with the number of reflow cycles and aging time. After the addition of SrTiO₃ nano-particles, in the solder ball region, a fine microstructure of AuSn₄, Ag₃Sn, Cu ₆Sn₅ intermetallic compounds appeared in the β-Sn matrix. In addition, the shear strength of solder joints containing SrTiO ₃ nano-particles exhibited a consistently higher value than that of plain Sn-Ag-Cu solder joints due to a second phase dispersion strengthening mechanism as well as a refinement of the intermetallic compounds. The fracture surface of plain Sn-Ag-Cu solder joints exhibited a brittle fracture mode with a smooth surface while Sn-Ag-Cu solder joints containing SrTiO₃ nano-particles showed ductile failure characteristics with rough dimpled surfaces. © 2010 Elsevier B.V. All rights reserved.