Interfacial reactions between Ni-Zn alloy films and lead-free solders

Abstract

Because of the miniaturization trend in electronic devices in recent years, semiconductor industry is striving hard to produce smaller and thinner devices while improving the performance and processing speed. The issue of reliability of solder joints in these miniaturized devices becomes very critical. In this study zinc is incorporated into the nickel barrier film in the form of Ni-Zn alloy by electrodeposition. The effects of the presence of Zn on the interfacial reactions between nickel barrier film and Sn-3.8Ag-0.7Cu and Sn-3.5Ag solders are investigated. Ni-Zn alloy films 1.73wt%Zn were prepared from ammoniacal diphosphate baths. Elemental composition of the alloy film was determined by energy dispersive x-ray spectroscopy (EDX) while x-ray diffraction method (XRD) was used to determine the phases present in the alloy film. Spreading rate was characterized with the use of optical microscope. Reflows were done for 1 and 12 cycles to investigate the effect of multiple reflows on the IMC growth and morphology. Results have shown that the IMC formed at the interface of SAC/Ni and SA/Ni was (Cu,Ni)5Sn6 and Ni3Sn4 respectively. (Ni,Cu)3Sn4 IMC was formed at the interface of SA/Ni-Zn alloy film. No spalling was detected at the SA/Ni-Zn solder joint. On the other hand, it has been observed that (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5 layer with continuous non-uniform morphology were formed on the SAC/Ni-Zn alloy film after 1x reflow. As the number of reflow increased, (Cu,Ni)6Sn5 layer spalled from the interface leaving only (Ni,Cu)3Sn4 IMC at the interfacial region.