Correlation between interfacial reactions and mechanical strengths of Sn(Cu)/Ni(P) solder bumps

Abstract

The correlation between interfacial reactions and mechanical strengths of Sn(Cu)/Ni(P) solder bumps has been studied. Upon solid-state aging, a diffusioncontrolled process was observed for the interfacial Ni-Sn compound formation of the Sn/Ni(P) reaction couple and the activation energy is calculated to be 42 KJ/mol. For the Sn0.7Cu/Ni(P), in the initial aging, a needle-shaped Ni-Sn compound layer formed on Ni(P). Then, it was gradually covered by a layer of the Cu-Sn compound in the later aging process. Hence, a mixture layer of Ni-Sn and Cu-Sn compounds formed at the interface. For the Sn3.0Cu/Ni(P), a thick Cu-Sn compound layer quickly formed on Ni(P), which retarded the Ni-Sn compound formation and resulted in a distinct Cu-Sn compound/Ni(P) interface. The shear test results show that the mixture interface of Sn0.7Cu bumps have fair shear strengths against the aging process. In contrast, the distinct Cu-Sn/Ni(P) interface of Sn3.0Cu solder bumps is relatively weak and exhibits poor resistance against the aging process. Upon the reflowing process, the gap formation at the Ni(P)/Cu interface caused a fast degradation in the interfacial strength for Sn solder bumps. For Sn0.7Cu and Sn3.0Cu solder bumps, Ni 3 P formation was greatly retarded by the self-formed Cu-Sn compound layer. Therefore, Sn(Cu) solder bumps show better shear strengths over the Sn solder bump.

Kinetic analysis of the interfacial reactions in Ni/Sn/Cu sandwich structures

“…Many researchers have reported that Ni-containing (Cu,Ni) 6 Sn 5 compounds tend to have a needlelike shape. 8,9 In Fig. 4, the thickness of the interfacial compound layers at both the Sn/Cu and Sn/Ni interfaces of the Ni/Sn/Cu sandwich samples are plotted.…”

Electromigration-Induced Failure of Ni/Cu Bilayer Bond Pads Joined with Sn(Cu) Solders

“…We can clearly observe the appearance of the typical needle-shaped morphology of the (Cu,Ni) 6 Sn 5 compound layer. [7][8][9] After 15 h of current stressing, unlike for the pure Sn/Ni/Cu joint, we found that the interfacial (Cu,Ni) 6 Sn 5 compound layer grew with the current stressing time. After a prolonged 25 h of current stressing, the interfacial (Cu,Ni) 6 Sn 5 compound layer grew even thicker (over 6 lm), much thicker than could possibly form for the same thermal annealing conditions but without the EM effect ( Fig.…”

Interfacial Reactions in Sn-0.7wt.%Cu/Ni-V Couples at 250°C

“…Its composition is Sn-13.5at.%Cu-26.8at.%Ni-0.3at.%V. Based on the Sn-Cu-Ni phase equilibria isothermal section 23 and previous Sn-Cu/Ni interfacial reaction studies, [8][9][10][11][12][13][14][15][16][17][18] it is the Ni 3 Sn 4 phase with 13.5at.%Cu solubility and very limited V solubility. Similar to the nomenclature of the Cu 6 Sn 5 phase, the Ni 3 Sn 4 phase in this study might be denoted the (Cu,-Ni) 3 Sn 4 phase in other studies.…”

“…Sn-0.7wt.%Cu alloy is a promising Pb-free solder, and is the base material for the most popular SAC solder. Besides, previous studies [9][10][11]13,[15][16][17] indicate that Ag does not participate actively in interfacial reactions with Ni. Thus an understanding of the interfacial reactions of Sn-0.7wt.%Cu/Ni-V couples is valuable for applications of both Sn-0.7wt.%Cu and SAC alloys.…”

“…There have been very intensive investigations on the interfacial reactions between Ni and the Sn-Cu and Sn-Cu-Ag solders, [8][9][10][11][12][13][14][15][16][17][18] and the results show that the reactions are very sensitive to Cu concentrations. When the temperature varies from 160°C to 250°C, the Cu 6 Sn 5 phase is the most common reaction product in Sn-Cu/Ni and Sn-Ag-Cu/Ni couples; however, the Ni 3 Sn 4 phase is formed when the Cu content in the solder is less than 0.5 wt.%.…”