Interfacial reactions and compound formation of Sn-Ag-Cu solders by mechanical alloying on electroless Ni-P/Cu under bump metallization

Abstract

Electroless Ni-P under bump metallization (UBM) has been widely used in electronic interconnections due to the good diffusion barrier between Cu and solder. In this study, the mechanical alloying (MA) process was applied to produce the SnAgCu lead-free solder pastes. Solder joints after annealing at 240°C for 15 min were employed to investigate the evolution of interfacial reaction between electroless Ni-P/Cu UBM and SnAgCu solder with various Cu concentrations ranging from 0.2 to 1.0 wt.%. After detailed quantitative analysis with an electron probe microanalyzer, the effect of Cu content on the formation of intermetallic compounds (IMCs) at SnAgCu solder/electroless Ni-P interface was evaluated. When the Cu concentration in the solder was 0.2 wt.%, only one (Ni, Cu) 3 Sn 4 layer was observed at the solder/electroless Ni-P interface. As the Cu content increased to 0.5 wt.%, (Cu, Ni) 6 Sn 5 formed along with (Ni, Cu) 3 Sn 4 . However, only one (Cu, Ni) 6 Sn 5 layer was revealed, if the Cu content was up to 1 wt.%. With the aid of microstructure evolution, quantitative analysis, and elemental distribution by x-ray color mapping, the presence of the Ni-Sn-P phase and P-rich layer was evidenced.

Solid–Solid Reaction Between Sn-3Ag-0.5Cu Alloy and Au/Pd(P)/Ni(P) Metallization Pad with Various Pd(P) Thicknesses

“…2c). Direct contact of Ni 2 SnP with solder has also been found previously in the literature; 25,26,[30][31][32][33][34][35][36] the Ni 2 SnP was exposed due to massive spalling of Ni 3 Sn 4 that is unlike that caused by the retarded growth of (Cu,Ni) 6 Sn 5 due to Pd(P) deposition (Fig. 2c).…”

Investigations of wetting properties of Ni–V and Ni–Co alloys by Sn, Sn–Pb, Sn–Cu, and Sn–Ag–Cu solders

“…Interfacial reactions change the interface, and the wetting properties are thus changed. For example, the reaction phase of the Sn/Ni system is the Ni 3 Sn 4 phase Gur and Bamberger, 1998;Kang and Ramachandran, 1980); the reaction phase of the Sn-0.7 wt%Cu/Ni system is the Cu 6 Sn 5 phase (Chen and Chen, 2001;Chen and Wang, 2006;Chen et al, 2002); the reaction phase of the Sn-3.0 wt%Ag-0.5 wt%Cu/Ni system is the Cu 6 Sn 5 and Ni 3 Sn 4 phase (Chiu and Lin, 2009;Kao and Duh, 2005;Kim et al, 2003). Because their interfacial reactions are different, their wetting properties are likely different.…”

Effects of Cu contents in flux on microstructure and joint strength of Sn–3.5Ag soldering with electroless Ni–P/Au surface finish

“…Additionally, the compositions of those Sn-Ni-Cu IMCs depend on the Cu concentration in the solder used [12]. For example, when using Sn-Ag-Cu solder with a low Cu content (<0.3 wt.%), the major interfacial intermetallic compound formed is (Ni, Cu) 3 Sn 4 [13,14]. On the other hand, (Cu, Ni) 6 Sn 5 is preferentially formed if the Cu concentration in the Cu-bearing solder is above 0.5 wt.% [13][14][15][16][17][18].…”