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A three‐dimensional, two‐phase computational model for simulating boiling‐enhanced mixed convection in free‐surface flows is presented. The associated constitutive models for the thermophysical and transport properties are described. A computational model incorporating the discrete‐element analysis was used to simulate the multi‐dimensional, two‐phase flow around a heated chip in a test tank filled with Freon‐(R113). Two and three‐dimensional simulations of both natural convection and nucleate boiling heat transfer regimes are presented. The velocity field, the temperature distribution, and the vapour concentration profiles are evaluated and discussed. The simulated heat fluxes are compared with the available experimental data. While the heat fluxes from the two‐dimensional simulation agree with the fluxes calculated for the three‐dimensional case, the flow in the tank is essentially three‐dimensional. The results show that there are secondary flows which cannot be captured by a two‐dimensional model. The heat flux in the boiling heat transfer regime is only about ten times larger than that in the natural convection regime due to the small vapour concentration in tank.

This paper aims to study the features of microstructures and mechanical properties of the joints which were produced by transient liquid phase method. The difference between phases in bonding region identified through metallography pictures and applying hardness and shear strength tests.

The bonding process was carried out at a temperature of 300°C for time durations ranging from 15 to 120 min. The scanning electron microscopy equipped with energy dispersive spectroscopy system and optical microscopy were used to examine microstructural characteristics, and mechanical properties of the joints were studied by applying microhardness and shear tests. The shear tests were conducted by a shear fixture which was mounted on the tensile machine.

The intermetallic compounds of the Cu₆Sn₅ −η and the Cu₃Sn-ε were formed simultaneously in the bonding interface. Although the η-phase, which exhibits scallop-shaped morphology, grows very quickly, upon completion of the isothermal solidification stage, it turns into the ε-phase. The hardness of the bonding interface is significantly higher than that of the substrate. The shear results show that once the bonding process is complete, brittle fracture occurs. Moreover, a greater decrease in strength was observed when the ε-phase is the only phase in the bonding region.

The hardness number of the η-phase is higher than that of the ε-phase. The hardness numbers of the η-phase and the ε-phase are 894 and 689 HV, respectively. The mean shear strength values of the samples that were bonded at 300 °C for 15, 60 and 120 min were 11.7, 9.5 and 5.4 MPa, respectively.

This paper aims to examine the effects of bonding temperature, bonding time, bonding pressure and the presence of a Pt catalyst on the bonding strength of Cu/SB/P-Cu/SB/Cu joints by transient liquid phase bonding (TLPB).

TLPB is promising to assemble die-attaching packaging for power devices. In this study, porous Cu (P-Cu) foil with a distinctive porous structure and Sn-58Bi solder (SB) serve as the bonding materials for TLPB under a formic acid atmosphere (FA). The high surface area of P-Cu enables efficient diffusion of the liquid phase of SB, stimulating the wetting, spreading and formation of intermetallic compounds (IMCs).

The higher bonding temperature decreased strength due to the coarsening of IMCs. The longer bonding time reduced the bonding strength owing to the coarsened Bi and thickened IMC. Applying optimal bonding pressure improved bonding strength, whereas excessive pressure caused damage. The presence of a Pt catalyst enhanced bonding efficiency and strength by facilitating reduction–oxidation reactions and oxide film removal.

Overall, this study demonstrates the feasibility of low-temperature TLPB for Cu/SB/P-Cu/SB/Cu joints and provides insights into optimizing bonding strength for the interconnecting materials in the applications of power devices.

In recent years, electronic devices have increasingly employed printed circuits produced using electrically conductive adhesives, commonly known as polymer thick films. This method is much more cost‐effective and efficient than other methods of wiring, including those using chemical etching or plating. In the past, the use of metal‐filled polymers as conductors in printed circuit fabrication has suffered from several limitations such as poor solderability, conductivity and adhesion. A new electrically conductive metal‐filled polymer formulation has been developed which overcomes these problems inherent in typical polymer thick film inks. This new product is based on transient liquid‐phase sintering wherein the metallic components of the formulation sinter at a relatively low temperature, resulting in a highly conductive continuous metal network. The sintering is achieved through the interaction of several metallic components with an adhesive‐flux component. The final product is highly conductive, solderable and exhibits excellent adhesion to a wide range of substrate materials. A new process for manufacturing fine‐line printed circuit boards using this ink technology is under investigation. It promises potentially simpler processing and lower cost than plating. In this new process, traces (in the form of troughs in the dielectric) are imaged using conventional photoimageable dielectrics. Exposure and developing conditions depend upon the polymer system used. The transient liquid phase sinterable conductive ink is applied to fill the photo‐exposed conductor pattern. Next, another layer of photoimageable dielectric is applied over the traces and imaged with vias for interconnections with subsequent layers. The dielectric is then cured and the ink applied to fill the vias. These steps may be repeated several times to produce low‐profile fine‐line multilayer printed circuits. This process for producing multilayer circuits using conductive inks simplifies the manufacturing of printed circuits, reduces profile, eliminates most waste in manufacturing, and reduces cost compared with plating.

The paper aims to fabricate an α-tricalcium phosphate (TCP) scaffold with an interconnected porous structure via selective laser sintering (SLS). To inhibit the phase transformation from β- to α-TCP in fabrication process of porous scaffolds, a small amount (1 weight per cent) of poly (L-lactic acid) (PLLA) is added into β-TCP powder to introduce the transient liquid phase.

The paper opted for the transient liquid phase of melting PLLA to decrease the sintering temperature in SLS. Meanwhile, the densification of β-TCP is enhanced with a combined effect of the capillary force caused by melting PLLA and the surface energy of β-TCP particles. Moreover, the PLLA will gradually decompose and completely disappear with laser irradiation.

The testing results show the addition of PLLA enables the scaffolds to achieve a higher β-TCP content of 77 ± 1.49 weight per cent compared with the scaffold sintered from β-TCP powder (60 ± 1.65 weight per cent), when the laser energy density is 0.4 J/mm2. The paper provides the mechanism of PLLA inhibition on the phase transformation from β- to α-TCP. And the optimum sintering parameters are obtained based on experimental results, which are used to prepare a TCP scaffold with an interconnected porous structure via SLS.

This paper shows that the laser energy density is an important sintering parameter that can provide the means to control the micro-porous structure of the scaffold. If the laser energy density is too low, the densification is not enough. On the other hand, if the laser energy density is too high, the microcracks are observed which are attributed to the volume expansion during the phase transformation from β- to α-TCP. Therefore, the laser energy density must be optimized.

The paper provides a feasible method for fabricating TCP artificial bone scaffold with good biological and mechanical properties.

The purpose of this paper is to develop a coupled lattice Boltzmann model for the simulation of the freezing process in unsaturated porous media.

In the developed model, the porous structure with complexity and disorder was generated by using a stochastic growth method, and then the Shan-Chen multiphase model and enthalpy-based phase change model were coupled by introducing a freezing interface force to describe the variation of phase interface. The pore size of porous media in freezing process was considered as an influential factor to phase transition temperature, and the variation of the interfacial force formed with phase change on the interface was described.

The larger porosity (0.2 and 0.8) will enlarge the unfrozen area from 42 mm to 70 mm, and the rest space of porous medium was occupied by the solid particles. The larger specific surface area (0.168 and 0.315) has a more fluctuated volume fraction distribution.

The concept of interfacial force was first introduced in the solid–liquid phase transition to describe the freezing process of frozen soil, enabling the formulation of a distribution equation based on enthalpy to depict the changes in the water film. The increased interfacial force serves to diminish ice formation and effectively absorb air during the freezing process. A greater surface area enhances the ability to counteract liquid migration.

The purpose of this paper is to quickly manufacture full Cu₃Sn-microporous copper composite joints for high-temperature power electronics applications and study the microstructure evolution and the shear strength of Cu₃Sn at different bonding times.

In this paper, a novel structure of Cu/composite solder sheet/Cu was designed. The composite solder sheet was made of microporous copper filled with Sn. The composite joint was bonded by thermo-compression bonding under pressure of 0.6 MPa at 300°C. The microstructure evolution and the growth behavior of Cu₃Sn at different bonding times were observed by electron microscope and metallographic microscope. The shear strength of the joint was measured by shear machine.

At initial bonding stage the copper atoms in the substrate and the copper atoms in the microporous copper dissolved into the liquid Sn. Then the scallop-liked Cu₆Sn₅ phases formed at the interface of liquid Sn/microporous copper and liquid Sn/Cu substrates. During the liquid Sn changing to Cu₆Sn₅ phases, Cu₃Sn phases formed and grew at the interface of Cu₆Sn₅/Cu substrates and Cu₆Sn₅/microporous copper. After that the Cu₃Sn phases continued to grow and the Cu₃Sn-microporous copper composite joint with a thickness of 100 µm was successfully obtained. The growth rule of Cu₃Sn was parabolic growth. The shear strength of the composite joints was about 155 MPa.

This paper presents a novel full Cu₃Sn-microporous copper composite joint with high shear strength for high-temperature applications based on transient liquid phase bonding. The microstructure evolution and the growth behavior of Cu₃Sn in the composite joints were studied. The shear strength and the fracture mechanism of the composite joints were studied.

This paper aims to present two Anand’s model parameter sets for the multilayer silver–tin (AgSn) transient liquid phase (TLP) foils.

The AgSn TLP test samples are manufactured using pre-defined optimized TLP bonding process parameters. Consequently, tensile and creep tests are conducted at various loading temperatures to generate stress–strain and creep data to accurately determine the elastic properties and two sets of Anand model creep coefficients. The resultant tensile- and creep-based constitutive models are subsequently used in extensive finite element simulations to precisely survey the mechanical response of the AgSn TLP bonds in power electronics due to different thermal loads.

The response of both models is thoroughly addressed in terms of stress–strain relationships, inelastic strain energy densities and equivalent plastic strains. The simulation results revealed that the testing conditions and parameters can significantly influence the values of the fitted Anand coefficients and consequently affect the resultant FEA-computed mechanical response of the TLP bonds. Therefore, this paper suggests that extreme care has to be taken when planning experiments for the estimation of creep parameters of the AgSn TLP joints.

In literature, there is no constitutive modeling data on the AgSn TLP bonds.

A numerical study of heat transfer enhancement due to the deformation of droplets at high Reynolds numbers is described. The two phase‐flow has been computed with a 3D DNS program using the volume‐of‐fluid method. The droplets are deformed because of the surrounding gas stream especially due to a sudden rise of flow velocity from zero to U_i. As the governing non‐dimensional parameter the Weber number of the droplets has been varied between 1.3 and 10.8 by assuming different surface tensions at Reynolds numbers between 360 and 853. The dynamical behavior of the droplets as a function of the Weber and the Ohnsorge number are in good agreement with experimental results from the literature. At the highest Reynolds number Re=853, a significant dependency of Nu on We has been found. The comparison of a Nusselt number computed with the real surface area with a Nusselt number computed with the spherical surface area shows that the heat transfer increases not only due to the droplet motion but also due to the larger surface area of the deformed droplet.

The purpose of this paper is to investigate the thermomechanical response of four well-known lead-free die attach materials: sintered silver, sintered nano-copper particles, gold-tin solders and silver-tin transient liquid phase (TLP) bonds.

This examination is conducted through finite element analysis. The mechanical properties of all die attach systems, including elastic and Anand creep parameters, are obtained from relevant literature and incorporated into the numerical analysis. Consequently, the bond stress-strain relationships, stored inelastic strain energies and equivalent plastic strains are thoroughly examined.

The results indicate that silver-tin TLP bonds are prone to exhibiting higher inelastic strain energy densities, while sintered silver and copper interconnects tend to possess higher levels of plastic strains and deformations. This suggests a higher susceptibility to damage in these metallic die attachments. On the other hand, the more expensive gold-based solders exhibit lower inelastic strain energy densities and plastic strains, implying an improved fatigue performance compared to other bonding configurations.

The utilization of different metallic material systems as die attachments in power electronics necessitates a comprehensive understanding of their thermomechanical behavior. Therefore, the results of the present paper can be useful in the die attach material selection in power electronics.