Showing papers by "Tomi Laurila published in 2013"

Thermodynamic reassessment of Au–Ni–Sn ternary system

Abstract: For having a better understanding on the formation and evolution of metal bonding interconnection microstructures the Au–Ni–Sn ternary system was reassessed on the basis of experimental results and the recently reported thermodynamical description for Au–Sn and Ni–Sn systems. In this paper, the thermodynamic parameters of Ni 3 Sn 4 phase were modified in order to achieve a better agreement with experimentally determined phase boundaries. Further, a self-consistent set of thermodynamic parameters for the Au–Ni–Sn system were obtained, which were able to reproduce most of the available experimental data. The Ni|80Au20Sn (wt%) diffusion couples were annealed at 320 °C for 10,000 s and at 150 °C for 2500 h. The microstructures of these samples were studied with SEM+EDS technique. The reaction interface between Ni and near eutectic AuSn alloy consisted of Ni 3 Sn/(Ni, Au) 3 Sn 2 /AuSn/Au 5 Sn layers. This experimentally observed diffusion path of Ni against Au–20 wt% Sn solder at 150 °C was rationalized on the basis of the thermodynamically calculated isothermal section.

Thermodynamic modeling of Au–Ce–Sn ternary system

Abstract: Phase relationships in Au–Ce–Sn ternary system have been thermodynamically modeled by using the CALPHAD technique. Out of the three binary systems, two systems (i.e. Au–Ce, and Sn–Ce) were thermodynamically assessed in this work, and the description of the third one (i.e. Au–Sn) was significantly improved from that of the previous one by adopting the recently published lattice stability of Sn(hcp). Ab initio calculations were employed to support the present thermodynamic assessment via calculating the enthalpies of formation of the relevant binary compounds as well as those of the two stoichiometric ternary compounds. All the intermetallic compounds in binary systems and two out of the seven ternary compounds were treated as stoichiometric phases. The other five ternary compounds were modeled with two or three sublattice sites based upon their homogeneity ranges. The solution phases, including liquid, fcc, bcc, hcp and dhcp, were modeled as substitutional solution phases. The Au–Ce–Sn ternary system was assessed by utilizing the thermodynamic descriptions of the three binary systems, and by taking into account the recently reported isothermal section at 750 °C. The set of thermodynamic parameters, obtained in this work, can be used to reproduce the experimentally determined phase equilibria at 750 °C. Besides, the liquidus projection was extrapolated utilizing the present database.

Improving the function of dopamine electrodes with novel carbon materials

Abstract: For therapeutic purposes, an accurate measurement of dopamine level in situ would be highly desirable. A novel strategy for the selective determination of dopamine concentration based on the diamond-like carbon (DLC) electrode is presented in this abstract. The developed DLC electrode is able to detect 10 μM dopamine and has improved sensitivity compared to platinum. Compared to carbon fiber electrodes, the DLC electrode is more stable because the background current is much lower.

Effect of isothermal annealing and electromigration pre-treatments on the reliability of solder interconnections under vibration loading

Abstract: Effects of two pre-treatment methods, isothermal annealing and DC-current stressing, on the reliability of solder interconnections under vibration loading has been studied in this paper. The results obtained show that: (1) isothermal annealing and DC-current stressing both compromise the reliability of interconnections during testing in comparison to the samples without pre-treatment and (2) the crack propagation path through the interconnection changes as compared to the samples without pre-treatments. The experimental results are rationalized with the help of detailed microstructural investigations coupled with the finite element method analysis. The DC-current stressing and isothermal annealing pre-treatments both soften the solder interconnections by inducing microstructural changes, which is reflected in the slightly reduced reliability under vibrational loading.