Effect of Cu Content on Performance of Sn-Zn-Cu Lead-Free Solder Alloys Designed by Cluster-Plus-Glue-Atom Model

The mechanical properties of solder alloys are a performance that cannot be ignored in the field of electronic packaging. In the present study, novel Sn-Zn solder alloys were designed by the cluster-plus-glue-atom (CPGA) model. The effect of copper (Cu) addition on the microstructure, tensile properties, wettability, interfacial characterization and melting behavior of the Sn-Zn-Cu solder alloys were investigated. The Sn29Zn4.6Cu0.4 solder alloy exhibited a fine microstructure, but the excessive substitution of the Cu atoms in the CPGA model resulted in extremely coarse intermetallic compound (IMC). The tensile tests revealed that with the increase in Cu content, the tensile strength of the solder alloy first increased and then slightly decreased, while its elongation increased slightly first and then decreased slightly. The tensile strength of the Sn29Zn4.6Cu0.4 solder alloy reached 95.3 MPa, which was 57% higher than the plain Sn-Zn solder alloy, which is attributed to the fine microstructure and second phase strengthening. The spreadability property analysis indicated that the wettability of the Sn-Zn-Cu solder alloys firstly increased and then decreased with the increase in Cu content. The spreading area of the Sn29Zn0.6Cu0.4 solder alloy was increased by 27.8% compared to that of the plain Sn-Zn solder due to Cu consuming excessive free state Zn. With the increase in Cu content, the thickness of the IMC layer decreased owing to Cu diminishing the diffusion force of Zn element to the interface.

Diffusion Spreading of the Emitted Metallurgical Gas

The main parameter which shows the space distribution of the emitted gas components is the rate of concentration decrease by the increase of the distance from the point where the emitted gas appears in the atmosphere. It is considered three different driving forces leading to the spreading of the emitted gas components from the centre of the metallurgical region to its periphery:  diffusion factor – the appearance of the emitted substance is the reason of the local concentration increase, it correlates with the diffusion process;  wind load factor – the wind movement acts always in advantage direction, wind force is not space homogeneous as the diffusion force is;  chemical factor – the intensity of chemical interaction of emitted components with the atmospheric ones influences the space distribution of the interaction products (secondary emissions). The proposed method allows to predict the space-time distribution of the emitted metallurgical gas by various external conditions.

Electrostatic-Directed Deposition of Nanoparticles on a Field Generating Substrate

ABSTRACTIn this paper we develop a Brownian dynamics model applied to position metal nanoparticles from the gas phase onto electrostatic-patterns generated by biasing P-N junction substrates. Brownian motion and fluid convection of nanoparticles, as well as the interactions between the charged nanoparticles and the patterned substrate, including electrostatic force, image force and van der Waals force, are accounted for in the simulation. Using both experiment and simulation we have investigated the effects of the particle size, electric field intensity, and the convective flow on coverage selectivity. Coverage selectivity is most sensitive to electric field, which is controlled by the applied reverse bias voltage across the p-n junction. A non-dimensional analysis of the competition between the electrostatic and diffusion force is found to provide a means to collapse a wide range of process operating conditions and an effective indicator or process performance.

Phase Distribution in the Cap Bubble Regime in a Duct

The lateral phase distribution in the cap-bubbly regime was analyzed with a three-dimensional three-field two-fluid computational fluid dynamics (CFD) model based on the turbulence model for bubbly flows developed by Lopez de Bertodano et al. [1994, “Phase Distribution in Bubbly Two-Phase Flow in Vertical Ducts,” Int. J. Multiphase Flow, 20(5), pp. 805–818]. The turbulent diffusion of the bubbles is the dominant phase distribution mechanism. A new analytic result is presented to support the development of the model for the bubble induced turbulent diffusion force. New experimental data obtained by Sun et al. [2005, “Interfacial Structure in an Air-Water Planar Bubble Jet,” Exp. Fluids, 38(4), pp. 426–439] with the state-of-the-art four-sensor miniature conductivity probe in a vertical duct is used to validate the three-field two-fluid model CFD simulations.

The Modeling of Lift and Dispersion Forces in Two-Fluid Model Simulations of a Bubbly Jet

Two-fluid model simulations of a bubbly vertical jet are presented. The purpose of these simulations is to assess the modeling of lift and turbulent dispersion forces in a free shear flow. The turbulent dispersion models used herein are based on the application of a kinetic transport equation, similar to Boltzmann’s equation, to obtain the turbulent diffusion force for the dispersed phase [1–4]. They have already been constituted and validated for the case of particles in homogeneous turbulence and jets [5] and for microscopic bubbles in grid generated turbulence and mixing layers [6,7]. It was found that it is possible to simulate the experimental data of Sun [8] (see Figs. 1–6) for a bubbly jet with 1 mm diameter bubbles. Good agreement is obtained using the model of Brucato et al. [9] for the modulation of the drag force by the liquid phase turbulence and a constant lift coefficient, CL. However, little sensitivity is observed to the value of the lift coefficient in the range 0<CL<0.29.

Forum on osmosis. IV. More on osmosis and diffusion

A brief summary is presented of the Gibbsian view of chemical drives and of its mechanical interpretation, including a description of the “diffusion force” that arises from an interplay between fluctuations and dissipation. Osmotic flows are shown to be driven by diffusion forces acting at the membrane interface, and not by the effects of Hammel and Scholander's “solvent tension.”