Interfacial reaction and mechanical reliability between Sn-3Ag-0.5Cu alloy and ultrathin-Ni(P)-type Au/Pd(P)/Ni(P)/Cu metallization pad

Recently, a Au/Pd(P)/Ni(P) surface finish with an ultrathin Ni(P) thickness (< 1 mu m) has received a great deal of attention from microelectronic industry because of the requirements of the fine-pitch packaging and the signal performance for high-frequency applications. The effect of Ni(P) and Pd(P) thickness on the solderability had been previously investigated in the literature; however, information regarding the P content effect of the Pd(P) film on this reliability issue is still seriously lacking to date. The focus of this study was to examine the interfacial reaction and mechanical reliability between a Sn-3Ag-0.5Cu alloy and an ultrathin-Ni(P)-type Au/Pd(xP)/Ni(P)/Cu metallization pad, where the thicknesses of Au/Pd(xP)/Ni(P) were 0.08 mu m/0.13 mu m/0.13 mu m and x were 0 wt%, 1-2 wt%, and 4-6 wt%. We found that the growth morphologies of intermetallic compounds (IMCs) at the Sn-3Ag-0.5Cu/Au/Pd(xP)/Ni(P)/Cu joints strongly depended on x and reflow number. The shear resistance of the solder joints could be greatly enhanced by reducing x, especially for one reflow; however, this difference was nearly alleviated after multiple reflows. This investigation provided valuable information about the role of P in the Sn-3Ag-0.5Cu/Au/Pd(P)/Ni(P)/Cu reaction system and the strategy to enhance the solderability of the Au/Pd(P)/Ni(P) surface finish.