Influence of Palladium Thickness on the Soldering Reactions Between Sn-3Ag-0.5Cu and Au/Pd(P)/Ni(P) Surface Finish

This study provides a comparison of the influence of Pd(P) thickness on reactions during soldering with the Sn-3Ag-0.5Cu alloy. Soldering was carried out in an infrared-enhanced conventional reflow oven, and a multiple reflow test method (up to ten cycles) was performed. With increasing Pd(P) thickness, the (Cu,Ni) 6 Sn 5 grew more slowly at the solder/Ni(P) interface, while the Ni 2 SnP/Ni 3 P bilayer became predominant after the first reflow. These three intermetallics, i.e., (Cu,Ni) 6 Sn 5 , Ni 2 SnP, and Ni 3 P, gradually coarsened as the number of reflow cycles increased. Furthermore, an additional (Ni,Cu) 3 Sn 4 layer appeared between (Cu,Ni) 6 Sn 5 and Ni 2 SnP, especially for the case of a thicker Pd(P) layer (0.2 μ m). The attachment of the (Ni,Cu) 3 Sn 4 to the Ni 2 SnP, however, was fairly poor, and a series of microcracks formed along the (Ni,Cu) 3 Sn 4 /Ni 2 SnP interface. To quantify the mechanical response of the interfacial microstructures, shear testing was conducted at two different shear speeds (0.0007 m/s and 2 m/s). The results indicated that the interfacial strength and the Pd(P) thickness were strongly correlated.