The influence of addition of Al nano-particles on the microstructure and shear strength of eutectic Sn–Ag–Cu solder on Au/Ni metallized Cu pads

In order to identify the effect of the addition of Al nano-particles to eutectic Sn–Ag–Cu solder, the interfacial microstructure between the solder and Au/Ni metallized Cu pad ball grid array substrates has been investigated as a function of multiple reflow cycles as well as aging time. Also the strength of the solder joints was evaluated by a ball shear test. In Sn–Ag–Cu solder joints and solder joints containing Al nano-particles, a scallop-shaped Sn–Ni–Cu intermetallic compound layer was clearly observed at the interfaces after long time aging and multiple reflows, and the intermetallic compound layer thickness was substantially increased with an increase in the number of reflow cycles as well as the aging time. However, after the addition of Al nano-particles, an additional Sn–Al–Ag intermetallic compound was found on the top surface of the Sn–Ni–Cu intermetallic compound layer. The Sn–Ag–Cu solder joints containing 3 wt% Al nano-particles consistently displayed a higher shear strength than that of the plain Sn–Ag–Cu solder joints as well as a lower Al nano-particle content as a function of reflow cycles and aging time due to a second phase dispersion strengthening mechanism by the formation of fine Sn–Ag–Al intermetallic compound particles as well as a controlled fine microstructure.