Jiunn Chen

Towards elastic anisotropy and strain-induced void formation in Cu–Sn crystalline phases

The Cu-Sn alloys have been used since ancient times. At present they attract much interest since the formation and growth of Cu-Sn intermetallic compounds, namely, Cu3Sn and Cu6Sn5, play an important role in the kinetics of the soldering reaction in microelectronics packaging. Their formation kinetics as well as mechanical properties has shown to be crucial for the integrity of solder joints. In this work, we report elastic properties of Cu3Sn and Cu6Sn5 crystalline phases using first-principles calculations based on the density functional theory. The elastic anisotropy of these phases, which is difficult to resolve from experiments, is fully discussed. Our results show that both crystalline phases have the greatest stiffness along the c direction. In particular, Cu3Sn exhibits in-plane anisotropy, which is associated with the lattice modulation within the superstructure. We also propose a void formation mechanism based on the computed bond anisotropy of Sn-Cu and Cu-Cu in Cu3Sn.

Electromigration reliability and morphologies of Cu pillar flip-chip solder joints

The Cu pillar is a thick under bump metallurgy (UBM) structure developed based on the consideration of alleviating current crowding in a flip-chip solder joint in operation conditions. We present in this work electromigration reliability and morphologies of Cu pillar flip-chip solder joints formed by joining Ti/Cu/Ni UBM with largely elongated Cu at ~62 mum onto Cu substrate pad metallization through the Sn-3Ag-0.5Cu solder alloy. Three test conditions that controlled averaged current densities in solder joints and ambient temperatures were considered: 10 kA/cm2 at 150degC,10 kA/cm2 at 160degC, and 15 kA/cm2 at 125degC.Electromigration reliability of this particular solder joint turns out to be much enhanced compared to a conventional solder joint with thin-film-stack UBM. Cross-sectional examinations of solder joints upon failure indicate that cracks formed in (Cu,Ni)6Sn5 or Cu6Sn5 intermetallic compounds (IMCs) near the cathode side of the solder joint. Moreover, the ~52 mum thick Sn-Ag-Cu solder after long-term current stressing has turned into a combination of ~80% Cu-Ni-Sn IMC and ~20% Sn-rich phases, which appeared in the form of large aggregates that in general distributed on the cathode side of the solder joint.

Performance of a Mott detector for undulator-based spin-resolved spectroscopy

To measure spin-polarized core-level electron spectra, a spectrometer equipped with a highly efficient retarding-potential Mott spin polarimeter using undulator-based soft-x-ray beamlines has been set up. With a thin film of Au as a target this polarimeter has an efficiency estimated to be ∼2×10−4. The performance of this system for spin-polarized spectroscopy has been tested using core-level spin-polarized photoemission of magnetic and nonmagnetic thin films excited with linearly and circularly polarized light, respectively. Measurements using a new spin-resolved absorption technique are also discussed.

Electronic structure and transport properties of La0.7Ce0.3MnO3

X-ray absorption spectroscopy (XAS), optical reflectance spectroscopy, and the Hall effect measurements were used to investigate the electronic structure in

ELECTRON CORRELATION EFFECTS IN HALF-METALLIC TRANSITION METAL OXIDES

{\mathrm{La}}_{0.7}{\mathrm{Ce}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}

Mechanical Properties of Cu 6 Sn 5 , Cu 3 Sn, and Ni 3 Sn 4 Intermetallic Compounds Measured by Nanoindentation

thin films (LCeMO). The XAS results are consistent with those obtained from

Anisotropic O 2p-Mn 3d unoccupied states in La1−xMnO3: an X-ray absorption spectroscopy study

\mathrm{LDA}+U

Identification of mechanical properties of Cu 6 Sn 5 , Cu 3 Sn, and Ni 3 Sn 4 intermetallic compounds using nanoindentation

calculations. In that the doping of Ce has shifted up the Fermi level and resulted in marked shrinkage of hole pockets originally existing in

First-Principles Calculations of Elastic Properties of Cu

{\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}

_{3}

(LCaMO). The Hall measurements indicate that in LCeMO the carriers are still displaying the characteristics of holes as