|Source||CMES: Computer Modeling in Engineering & Sciences, Vol. 109, No. 1, pp. 1-13, 2015|
|Download||Full length paper in PDF format. Size = 613,546 bytes|
|Keywords||Interfacial adhesion strength, Under bump metallurgy, First-principles density functional theory calculation, Solder bump.|
This study aims at exploring the interfacial adhesion strength between solder bump and four typical under bump metallurgies (UBMs), i.e., Cu/Ni, Cu/TiW, Cu/Ni/Cr and /Cu/V/Cr, at atomistic scale. The average bond length and interfacial adhesion stress of the Sn-3.5Ag/Cu/Ni, Sn-3.5Ag/Cu/TiW, Sn-3.5Ag/Cu/Ni/Cr and Sn-3.5Ag/Cu/V/Cr micro-bump interconnects are calculated through the firstprinciples density functional theory (DFT) calculation to estimate the interfacial adhesion strength between the solder bump and UBMs. In addition, by investigating the electric field effect on the average bond length and adhesive stress, the combination of solder bump and UBM with better interfacial adhesion strength and electromigration resistance ability can be determined. The results show that the interfacial adhesion strength between solder bump and wetting layer is much weaker than those of other interfaces, implying that the interfacial failure, induced by the electromigration, is likely to occur at the interface between solder bump and wetting layer. It is also found that the Sn-3.5Ag/Cu/Ni micro-bump interconnect would possess much stronger interfacial adhesion strength at the interface between solder bump and wetting layer than the other micro-bump interconnects. In addition, in comparison with the TiW and V metals, the Ni metal as the diffusion barrier layer can yield much stronger interfacial adhesion strength with wetting layer. Finally, as the adhesion layer is made of Cr metal, the Ni metal, acting as diffusion barrier layer, would hold much stronger interfacial adhesion strength than that of V metal.