Chih-chi Chen

Interfacial reactions in the Sn-(Ag)/(Ni,V) couples and phase equilibria of the Sn-Ni-V system at the Sn-Rich corner

Ni-7wt.%V is commonly used as the barrier layer material in the under-bump metallurgy in the microelectronic industry. Although interfacial reactions between various solders with the nickel substrate have been investigated intensively, the effects of vanadium addition upon the solder/(Ni,V) interfacial reactions have not been studied. Sn/(Ni,V) and Sn-Ag/(Ni,V) interfacial reactions at 250°C were investigated in this study using the reaction couple technique. The vanadium contents of the (Ni,V) substrates examined in this study are 3 wt.%, 5 wt.%, 7 wt.%, and 12 wt.% and the reaction time is 12 h. The results indicate that when the vanadium contents in the (Ni,V) substrate are 5 wt.% and higher, the Sn/(Ni,V) and Sn-Ag/(Ni,V) interfacial reactions are different from those in the solder/Ni couples. Besides the Ni3Sn4 phase as commonly formed in the reaction with Ni substrate, a new ternary T phase has been found, and the reaction path is L/Ni3Sn4/T/(Ni,V). A 250°C Sn-Ni-V isothermal section is proposed based on the three constituent binary systems and limited experimental results obtained in this study. The reaction path is illustrated with the proposed Sn-Ni-V isothermal section. No stable ternary Sn-Ni-V phase is found from the phase equilibria study, and the new T phase is likely a metastable phase.

Solid/solid interfacial reactions between Sn-0.7 wt% Cu and Ni-7 wt% V

Sn–0.7 wt% Cu alloy is an important Pb-free solder, and Ni–7 wt% V is the major diffusion barrier layer material of flip chip technology. Reactions at the Sn–0.7 wt% Cu/Ni–7 wt% V interface are examined at 160, 180, and 210 °C. Only the Cu 6 Sn 5 phase is formed in the Sn–0.7 wt% Cu/Ni–7 wt% V couple reacted at 160 and 180 °C; however, in addition to the Cu 6 Sn 5 and Ni 3 Sn 4 phases, a quaternary Q phase is formed in the Sn–0.7 wt% Cu/Ni–7 wt% V couple reacted at 210 °C. The Q phase is a mixture of nanocrystalline Ni 3 Sn 4 phase and an amorphous phase. With longer reaction time at 210 °C in the Ni–V/Q/Sn–Cu couple where the Q phase is in direct contact with solder, the Ni 3 Sn 4 phase nucleates inside the preformed Q phase, and the alternating layer phenomenon Ni–V/Q/Ni 3 Sn 4 /Q/Ni 3 Sn 4 /Cu 6 Sn 5 /Sn–Cu is observed. The interesting solid state amorphization and alternating layer phenomena at 210 °C are primarily caused by the fact that Sn and Cu are fast diffusing species, while V is relatively immobile.

Electromigration effects upon the Sn∕Ni–7wt%V interfacial reactions

The electromigration effects upon the Sn∕Ni–7wt%V interfacial reactions are examined. A ternary T phase was formed in the Sn∕Ni–7wt%V couple reacted at 200°C in the early stage. The reaction phases became T∕Ni3Sn4 and an interesting T∕Ni3Sn4∕T∕Ni3Sn4 alternating layer structure with longer reaction time. The passage of electric current of 500A∕cm2 density through the couple alters the reaction rates and the phase progression time. At the interface with electrons flow concurrently to the diffusion of Sn atoms, the reaction rates are enhanced.

Amorphization of Ti1−x Mn x

Three amorphous Ti1−xMnx alloy powders, withx = 0.4, 0.5, and 0.6, were prepared by mechanical alloying (MA) of the elemental powders in a high-energy ball mill. The amorphous powders were characterized by X-ray diffraction (XRD) and high-resolution transmission elec- tron microscopy (HRTEM). The crystallization temperatures for these alloys detected by dif- ferential scanning calorimetry (DSC) varied from 769 to 830 K. The calculated enthalpies of mixing in these amorphous phases are relatively small compared with those for other Ti-base binary alloys. The criteria for solid-state amorphization reaction are examined. It is suggested that the kinetics of nucleation and growth favors the formation of the amorphous phases and the supply of atoms for nucleation and growth is predominantly through the defective regions induced by MA.