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 Ni2SnP/Ni3P bilayer became predominant after the first reflow. These three intermetallics, i.e., (Cu,Ni)(6)Sn-5, Ni2SnP, and Ni3P, 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 Ni2SnP, especially for the case of a thicker Pd(P) layer (0.2 mu m). The attachment of the (Ni,Cu)(3)Sn-4 to the Ni2SnP, however, was fairly poor, and a series of microcracks formed along the (Ni,Cu)(3)Sn-4/Ni2SnP 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.