Interfacial Reaction and Mechanical Characterization of Eutectic Sn–Zn/ENIG Solder Joints during Reflow and Aging

Abstract

The interfacial reactions and joint reliabilities between Sn-9 mass%Zn solder and an electroless nickel-immersion gold (ENIG) plated Cu substrate were investigated during reflow and isothermal aging at temperatures between 343 and 423 K for aging times of up to 2400 h. After reflowing and aging, the intermetallic compound (IMC) formed at the interface was found to be AuZn 3 . No Ni-containing reaction products, such as Ni-Zn, Ni-Sn and Ni 3 P, were observed to form at the interface. The interfacial microstructure and shear strength remained nearly unchanged, irrespective of the reflow time, and the fractures occurred in the solder matrix. In the ball shear tests conducted after aging treatment, the shear strength of the samples decreased during the initial 100 h of aging and then remained constant with prolonged aging. The interfacial reaction between the Sn-Zn solder and the Ni-P plating layer was found to be suppressed by the formation of a layer-type Au-Zn IMC layer, resulting in the desirable interfacial reaction. Compared to the fast interfacial reaction between the Sn-9Zn solder and Cu substrate, the Sn-9Zn/ ENIG solder joint was considered to have a superior joint reliability.

Investigation of interfacial reactions between Sn–Zn solder with electrolytic Ni and electroless Ni(P) metallization

“…Most interestingly, there was no P-rich Ni compound observed at the resolution limit of the SEM used. The absence of P-rich Ni layer at the interface of the Sn-Zn solder/Ni(P) system was also confirmed by other researchers [15,18]. The average thickness of intermetallic layers was 0.8-1.2 m. In the initial reflow condition, the IMCs on the Ni(P) metallization were mainly composed of Au-Ni-Sn-Zn.…”

“…It is consistent with the high value of their shear strengths. Yoon et al also observed no deterioration of the joint strength of the Sn-Zn solder/Ni(P) system even after 120 min of reflow [15]. Fig.…”

Reliability studies of Sn–9Zn/Cu solder joints with aging treatment

“…Consequently, the results of interfacial reaction and shear test showed that the Sn-9Zn/Cu solder joint has an undesirable joint reliability. Recently, we have also investigated the interfacial reactions and mechanical properties of the Sn-9Zn/ENIG plated Cu joints during isothermal aging, and the results are reported elsewhere [22]. According to the result, during the reflow process, Au did not dissolve into the solder and AuZn 3 IMC layer formed by the fast reaction of Au and Zn.…”

Effects of Zn-Containing Flux on Sn-3.5Ag Soldering with an Electroless Ni-P/Au Surface Finish: Microstructure and Wettability

“…Moreover, it was also reported that a Au-Zn-Ni-Sn intermetallic compound was present at the joint interface between Sn-9Zn and the Ni-P/Au plating layer. 22,27 According to a study of a Sn-3Ag-0.5Cu BGA ball attached to a Ni-P/Au pad using a Sn-8Zn-3Bi solder paste, the reflow temperature, and perhaps time, had a significant effect on the type of interfacial intermetallic compound formed. 23 Specifically, a low peak reflow temperature of 210°C gave a predominantly Au-Zn layer, but when applying a high reflow condition with a peak temperature of 240°C, an interfacial Ni-Sn-Cu-Zn layer appeared instead of Au-Zn intermetallics.…”

“…In previous studies of soldering systems of the Sn-Zn family with the ENIG surface finish, formation of fine Zn-containing intermetallic compounds was observed at the joint interfaces. [20][21][22][23][24][25][26][27] This indicates that the intervention of Zn in the interfacial reaction proceeds in this soldering system. Therefore, from the aspect of controlling the interfacial reaction, addition of a Zn compound to the flux should demonstrate interesting behavior at the joint interface when soldering on a Ni-P/Au plating layer.…”