Retardation of Massive Spalling by Palladium Layer Addition to Surface Finish

摘要

The reactions between a Sn-3Ag-0.5Cu solder alloy and Au/Pd(P)/Ni(P) surface finishes with various Pd(P) layer thicknesses (0, 0.05, 0.1 μm) were examined at 235°C for the effect of Pd(P) on the massive spalling of an intermetallic compound (IMC). The deposition of a thin Pd(P) layer between the electroless Ni (7 μm) and immersion Au (0.06 μm) plating on the Cu substrate significantly retarded the massive spalling of (Cu,Ni)6Sn5 layer during reflow. Its retarding effect increased with increasing the EP layer thickness. The retardation of the massive spalling was attributed to an enhanced Cu diffusion from the Cu substrate across the Ni layer so that the (Cu,Ni) 6Sn_5 layer could grow continuously at the solder/Ni interface without depleting the Cu in the solder.