Huijun Cao

Numerical Simulation Study on Barrel Erosion of Ion Thruster Accelerator Grid

The barrel erosion, one type of accelerator grid erosion in an ion thruster, is important and needs more detailed studies. In this paper, a three-dimensional numerical simulation code is developed using a hybrid immersed-finite-element particle-in-cell method and Monte Carlo collisions method; the dynamics of a neutral atom is modeled using a direct simulation Monte Carlo method; and a numerical simulation study is run to investigate the mechanism of aperture barrel erosion of an ion thruster accelerator grid. Simulation results indicate that the aperture barrel erosion of ion thruster accelerator grid is entirely caused by the charge-exchange ions under nominal operating condition, and the incident charge-exchange ions in four regions, namely the upstream region, the extraction (center) region, the extraction (edge) region, and downstream of the accelerator grid, are the causes of aperture barrel erosion. High-energy charge-exchange ions originated from upstream region are not well focused and play an im...

Cathodic peeling damage of Cu6Sn5 phase in Cu/SnAg3.0Cu0.5/Cu bridge interconnections under current stressing

The cathodic interfacial damage behavior that has been attributed to electromigration is serious but has often been confused with thermomigration damage in solder interconnections. In this paper, after the effects of the non-uniform temperature distribution of Cu/SnAg3.0Cu0.5/Cu bridge joints are decoupled from the effects of the current stress, the microstructural evolution of the cathodic Cu6Sn5 phase is investigated under an average current density of 7.12 × 107 A·m−2 for 0–350 h. The results show that the interfacial Cu6Sn5 peels rather than dissolving completely at the cathode, because of both adhesion degradation at the Cu6Sn5/Cu interface and sustained cathodic stresses. This unrecorded peeling behavior will contribute to the rapid formation of interfacial voids and will thus dramatically increase the risk of interfacial failure. Fortunately, by restricting the intergranular diffusion and enhancing the bond strengths between adjacent Cu6Sn5 grains, an aging pre-treatment of the solder joints is fou...

Formation mechanism and reliability of Cu 6 Sn 5 textures formed in-between liquid Sn and (111)/(001) Cu single crystals

Formation mechanism and reliability of the Cu<inf>6</inf>Sn<inf>5</inf> textures formed in-between the liquid SnCu<inf>0.7</inf> solder and (111)/(001) Cu single crystals were studied in this paper. Regular arrays of the roof-type Cu<inf>6</inf>Sn<inf>5</inf> grains with the fixed intersecting angles were generated on both types of Cu single crystals after soldering at 250°C for 1 min. The formation mechanism of these Cu<inf>6</inf>Sn<inf>5</inf> roofs was confirmed to be a hexagonal-rod-type growth mode due to morphology and orientation analyses. In addition, based on the shear tests of the actual solder joints, the Cu<inf>6</inf>Sn<inf>5</inf> textures formed on (111)/(001) Cu single crystals were affirmed to be ideally suitable for use as the reliable interfacial connection layers to resist shear failures in electronic packaging.