Interfacial microstructure and mechanical reliability of the Sn-Ag-Cu/Au/Pd(xP)/Ni(P) reactive system: P content effects

Abstract Electroless deposition of a palladium film, e.g., pure Pd or Pd(P), between Au and Ni(P) films has received a great deal of attention from the microelectronic industry over the past decade. We investigated the effect of P on the solderability and the corresponding mechanical reliability of the Sn-3Ag-0.5Cu/Au/Pd( x P)/Ni(P)/Cu joint system, where x  = 0, 3, and 4.5 wt%. Analyses of electron probe X-ray microanalysis and field-emission transmission electron microscopy showed that a trilayer of (Cu,Ni) 6 Sn 5 /(Ni,Cu) 3 Sn 4 /Ni 3 P intermetallic structure grew at the interface at x  = 0 wt%, and the growth of (Ni,Cu) 3 Sn 4 was replaced by that of Ni 2 SnP at x  = 3 and 4.5 wt%. In high-speed ball shear testing, the microstructure transition induced by P addition would cause a fracture mode change from brittle to ductile, and increased the shear resistance of solder joints. These findings indicated that the P content in the Pd(P) film is a crucial factor in interfacial strength, and an appropriate amount of P is beneficial to the solderability of the Au/Pd( x P)/Ni(P) surface finish.