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Cu/Sn wafer-level bonding is an interesting solution for wafer-to-wafer stacking technologies, due to its compatibility with 3D interconnections as well as vacuum sealing applications. The Cu/Sn eutectic bonding process is favored by industry and researchers alike for its excellent process compatibility and low cost, and has been proven for high density interconnect packaging of MEMS devices. Because of the presence of heterogeneous materials (TSV -Cu, Si substrates, Cu bumps, and Sn bumps) with large differences in coefficients of thermal expansion, the Cu/Sn interface exists varying degrees of stress and strain during the bonding process which can have an impact on the reliability of the bonding results. By optimizing the layout of the Cu/Sn bumps and the parameters of the bonding process, the stress and strain distribution during the bonding process can be reduced and the reliability of the Cu/Sn bonding interface can be improved. Based on ANSYS finite element steady-state thermodynamic analysis the stress and strain distribution at the bonding interface can be effectively obtained for different Cu/Sn bump layout, reducing the strain on the bump surface during the bonding process and improving the process reliability by optimizing the design rules.

Vacuum packaging of Micro-electro-mechanical system (MEMS) devices is a hot topic for its advantages of improving performance and reducing power consumption. In this paper, the physics package of a chip scale atomic clock (CSAC), as a typical kind of MEMS device, is performed by vacuum packaging based on a systematic method proposed by us. The whole process, including low outgassing and thermal stable materials selection, prebaking for desorption, getter firing for absorption and solder reflow for vacuum sealing is introduced thoroughly. The thermogravimetric analysis or thermal gravimetric analysis (TGA) is used to analyze the thermal stability and desorption of materials. The leak rate of physics packages is measured to be less than 4 × 10−10 Pa·m3/s by helium leak detection. The residual gas pressure and composition in physics packages are analyzed after vacuum packaging. The results show a high vacuum ~0.1 Pa in the physics package. The frequency stability is improved from 4.68 × 10−11 to 1.07 × 10−11 @40,000 s. The presented method for high vacuum packaging is also applicable to other MEMS devices.

The high thermal conductivity, lightweight, and low cost of aluminum (Al) make it a promising substrate material for high power electronic and photonic packages and housings. It is particularly attractive for aerospace and space applications due to its lightweight. A main challenge for these applications is poor bondability. The native aluminum oxide (Al2O3) prevents aluminum from bonding by using popular die-attach materials such as solders. Zincating process is often needed to dissolve the Al2O3 layer and deposit a protection zinc layer which provides a basis for subsequent metallization or soldering process. However, the zincating and metallization processes could increase the processing cost and bring more reliability issues. In this research, a novel Ag foil bonding technique has been developed to bond Ag foils directly to Al substrates to produce Ag-cladded Al substrates. Two Ag-Al bonding processes are developed: solid-state and eutectic. Subsequently, Si chips are bonded to the Ag-cladded Al substrates using solid-state process at 300 °C without any additional die-attach material. For the Ag-Al bonding processes, no surface treatment is applied to Al substrates to remove the native Al2O3 layer. In the Ag-Al soli-state bonding process, Ag and Al atoms inter-diffused through the thin Al2O3 to react and form Ag2Al and Ag3Al compounds. In the Ag-Al eutectic bonding process, Ag2Al+(Al) eutectic structure forms at the Ag/Al interface without Ag3Al compound formation. The native Al2O3 layer, a potential fracture path, is broken into pieces during eutectic reaction and possibly dispersed into the eutectic structure. Shear test results of Si/Ag/Al joint samples far exceed the military criterion (MIL-STD-883H method 2019.8). The Si/Ag/Al structures break either along the Ag/Al interface or within the Si chip. With the advantages of high thermal conductivity, high reliability, lightweight, and process simplicity, the Ag-cladded Al structures should be highly valuable for applications in packages and housings where lightweight and high heat-conducting are necessary.

Thermal management of microprocessors and power electronics face major challenges including but not limited to a need for reliable and mechanically robust micro-cooler and micro-heat spreader devices. While the thermofluidic performances of the embedded microchannel with 3D manifold cooling and heat spreaders have received much attention (and carefully studied) for the past two decades, the challenges associated with the mechanical design and reliability have not been the focus of the research in thermal management community. Gold-tin eutectic bonding is proposed to attach silicon-based evaporator and condenser substrates in vapor chambers, as well as silicon microchannels substrate to silicon 3D manifold in high performance micro-coolers. The bonding interface in a silicon embedded microchannel to a silicon 3D manifold requires careful design to withstand pressures ~ 500 KPa, for target heat flux of ~ 1 kW/cm2 using single-phase water as working Evaporator and condenser bonding interface in a silicon-based vapor chamber must withstand water burst pressure of ~ 0.8 MPa when it is subjected to elevated temperature of 175 °C. In this study, a set of silicon microchannels in two substrates are fabricated using conventional microfabrication process, which then bonded using gold and tin multilayer composite structure (150 nm Au/75 nm Sn/150 nm Au) at 350 °C. Subsequently, the tensile stress is "directly" measured using carefully designed "test" samples, by means of applying direct tensile force to the sample. We measured tensile stress for 11 samples with contact areas ranging from 50 µm x 100 µm to 150 µm x 150 µm, the resulting stresses ranges from 2.0 to 5.5 MPa, with an average value of 3.2 MPa. Findings of this study will be largely beneficial in design and fabrication of silicon-based vapor chambers and high performance microchannel with 3D manifold coolers.

This paper reports a deep-UV LED (DUV-LED) package based on silicon MEMS process technology (Si-PKG). The package consists of a cavity formed by silicon crystalline anisotropic etching, through-silicon vias (TSVs) filled with electroplated Cu, bonding metals made of electroplated Ni/AuSn and a quartz lid for hermetic sealing. A DUV-LED die is directly mounted in the Si-PKG by AuSn eutectic bonding without a submount. It has merits in terms of size, heat dissipation, light utilization efficiency, productivity and cost over conventional AlN ceramic packages. Uniform light emission at an optical output of 30 mW and effective reflection on Si (111) slopes in the Si-PKG were observed.

In this paper, silicon substrate wafer level fabrication process of liquid cooling microchannel is introduced. Fig. 1 shows the microchannels fabricated on the silicon wafer surface. This microchannel component is to be integrated into a heat sink package served as an advance liquid cooling solution for high power server electronics cooling. Sambhaji [1] suggested liquid microchannel cooling method as more effective, reliable and lesser mechanical vibration to draw intense heat flux from high power electronic devices; compared with conventional air-flow convection cooling. Nicholas [2] illustrated micro structure jet impingement onto mirco-porous structure to eliminate flow instabilities, meeting high heat dissipation from concentrator photovaltics devices. Hence, novelty of multi-layers microchannel fabrication becomes the key to meet these requirements. This paper demonstrated using silicon wafer level process to build the main components of microchannels, micro-fins and jet impingement-nozzles. Fig. 2 shows these three main key components fabrication on silicon substrate. These structures were fabricated through silicon deep reactive ion etching process. Key process parameters were developed and optimized to meet structural dimensions control limits, uniformity and surface roughness conditions. Additional dielectric layers were added before the lithography patterning for silicon-etch to ensure smoother etched surface achieved after long process time of plasma etching process. Optimized proportion ratio of dielectric layers and photoresist layers thickness were evaluated to meet the plasma etching selectivity requirement between the silicon, dielectric and photoresist materials. The remainder oxide layer on the silicon surface is critical acting as an adhesive layer for subsequent metallization process. Liquid chemical etching process was used to remove the photoresist layer after silicon plasma etching. The key challenge within the fabrication process flow is to perform double sided silicon micro-structures fabrication. Silicon substrate as a carrier wafer to temporarily bonded on the microchannel surface in order to perform silicon etching process on the others side of wafer. Bonding materials and conditions were evaluated in order to ensure no delamination and breaking of silicon substrate during the silicon plasma etching on “structured” substrate. Optimized process flow was developed as well to ensure there is no penetration of chemicals and gas onto the bonding surface which could deteriorate the materials properties, consequently failed to debond or broken during the debonding process after the silicon plasma etching process completed. Metalization process was introduced to deposit eutectic bonding layers on the microchannel surfaces. Process flow sequences and conditions were established to ensure good bonding quality between the components layers without liquid leakage. Experimental flow test was carried out. This shows good pressure drop trend with increasing flow rate without leaking and blockage issue during the test. Experimental test show good repeatability results and illustrated good reliability results of the silicon microchannel samples.

Ultrathin buffer layers (UBLs) with varied thickness ranging from 10 to 100 nm and different materials were used in Cu/Sn eutectic bonding. A Cu/Sn film thinner than $2~\mu \text{m}$ could fully react and became stiff and rough Cu-Sn intermetallic compound layer, which leads to failure bonding. Four kinds of semiconductor compatible materials including Ti, Pd, Co, and Ni were inserted between Cu/Sn to delay interdiffusion prior to eutectic bonding. In addition to symmetric Cu/Sn bonding with UBL, asymmetric Cu/Sn-Cu bonding scheme with 50-nm Ni UBL was demonstrated. With good mechanical properties, bonding quality, and electrical characteristics, the application of submicrometer Cu/Sn wafer-level bonding by assistance of buffering layer gives a promising and flexible platform for future 3-D integration applications.

A series of Al-40Zn-5Si alloys with different additions of Eu were prepared by permanent mold casting. The nucleation phenomenon incorporating the modification of silicon phase was investigated by using the synchrotron radiation imaging technology, scanning electron microscopy, electron probe microanalysis and high resolution high-angle annular dark-field scanning transmission electron microscopy. It was found that the primary phase was α-Al dendrites and the pre-eutectic Si particles were precipitated continuously at the front of the solid/liquid interface in Al-40Zn-5Si alloys. The nodular pre-eutectic Si particles were observed when the Eu addition was 0.3%. Meanwhile, a flake-to-fibrous transition of eutectic Si was also observed. The needle-like eutectic Si crystals were seen to shoot out from the vicinity of primary α-Al dendrites into melt with high velocities leading the irregular eutectic interface in the unmodified Al-40Zn-5Si alloy. However, the eutectic grains with smooth interfaces nucleated mainly near primary or secondary α-Al branches in 0.3% Eu-modified Al-40Zn-5Si alloy. The eutectic grains began to nucleate on the nodular pre-eutectic Si particles when the α-Al surface reached so close to them. The formation of nodular pre-eutectic Si particles was attributed to the adsorption of Eu atoms along the growth direction of Si and at the intersection of Si twins. This is fully consistent with the well-known poisoning of twin plane re-entrant edge (TPRE) and the impurity induced twinning (IIT) modification mechanisms proposed for interpreting the modification of eutectic Si.

This paper presents micro-Pirani vacuum gauges using low-resistivity monocrystal silicon for the heaters and the heat sinks. We designed a new Pirani gauge with an embedded Wheatstone bridge made by thick-silicon resistors that allows an improvement in resolution and sensitivity. With the optimized Wheatstone bridge structure, the temperature coefficient of the gauges pressure measure decreases from 2.5%/°C to 0.74%/°C, and the resolution was optimized from 0.071 to 0.008 Torr at 1 Torr. In addition, the gauges were packaged into non-hermetic cavities by wafer-level AlGe eutectic bonding to undergo the wafer-dicing process, with sensitivity improved from 1.65 to 17.1 V/Torr at 1 Torr.

To fabricate a higher melting point joint by bonding at a low temperature, bonding characteristics of Au/Cu joints bonded at various bonding conditions using Sn-57Bi-1Ag solder were investigated. They were compared with those of the Cu/Cu joint. In the Au/Cu joint bonded at 170 oC for 1 min, a large scallop-shaped AuSn4 layer formed in the joint interface of Au and solder. A Au-diffused layer formed in the tip of the AuSn4 layer. The Sn-Cu-Au layer including approximately 20 mol% Au formed in the joint interface of Cu and solder. With increasing the bonding time, both the eutectic microstructure with β-Sn and Bi and the Au layer disappeared. As the result, the solder area changed from the eutectic microstructure to Bi phases including AuSn4 and Ag3Sn phases in the bonding time over 30 min. In contrast, the eutectic microstructure formed in the Cu/Cu joint bonded at 170 oC regardless of the bonding time. The bond strength of the Au/Cu joint was approximately one-third of that of the Cu/Cu joint. In both joints, the bond strength reduced with increasing the bonding time due to the fracture mode change.

Upward directional solidification experiments were carried out on various Pb-Sn alloys using water cooled copper chills. Different combinations of growth rate V and composition Co were used to investigate their effect on microstructure evolution during solidification. The effect of solidification velocity and composition on the structure formation is analyzed. It is observed that the hypoeutectic Pb-Sn alloys exhibit columnar dendritic structure with α phase rich region. In case of hypereutectic alloys the columnar dendritic structure is with β phase rich region. In both the cases dendritic structure was found to surround by the eutectic structure, a typical result of non equilibrium cooling. The eutectic composition exhibits complete eutectic structure aligned in the direction of solidification.

Technological process of manufacturing MEMS contains standard microelectronic operations and original technological processes. In this paper silicon wafers bonding process of eutectic soldering with thin gold layer deposited on the one of bonding wafer has been discussed. When testing samples after the process, the problem of uneven gold distribution across the substrate was discovered. To avoid the gold spreading effect during the bonding process a damping air clamp has been developed.

This study is focused on the effect of boron addition, in the range of 0.011 wt% to 0.048 wt%, on the solidification behavior and microstructure of U720Li alloy. It has been found that boron increased the eutectic (γ + γ′) precipitation significantly, while reduces the formation of η phase and Zr-rich particles precipitated in front of the eutectic (γ + γ′) obviously. Boron greatly retards the γ matrix solidification which is verified by the fact that it markedly reduces the ’segregated area’ around the final liquid pool or eutectic (γ + γ′). Based on this phenomenon, boron is assumed to form a layer at the solid/liquid interface and inhibits the attachment of atoms to attach on or jumping off the solid front, and hence lowers the γ matrix solidification rate. Boron increases the eutectic (γ + γ′) precipitation mainly by retarding the γ matrix solidification, which resulting in deeper undercooling and more eutectic forming elements such as Ti left in the residual liquids. Subsequently, boron reduces the η-Ni 3 Ti and Zr-rich phase formation because the increasing eutectic (γ + γ′) precipitation favors the consumption of Ti and dissolving Zr in γ′ phase.

Sb is an effective additive to modify eutectic Si of Al-Si alloys and the modification mechanism has not yet been studied very clearly. In this paper, computer aided cooling curve thermal analysis and microstructure assessment were carried out to investigate the modification effects of Sb on Al7SiMg alloy. The results show that the Sb addition amount of 0.1~0.25% has improvement effect on eutectic Si morphology, which can be further confirmed from the thermal analysis results. The addition of Sb decreases the eutectic growth temperature by 5 °C to 7.8 °C, indicating an undercooling effect resulted from Sb modification. Compared to that of short rods, a better eutectic Si morphology of nearly granular particles can be obtained in a faster cooling rate. The length of silicon has been gradually shortened as holding time increased to 2.5 h from 0.5 h, which means a long period modification effect of Sb in Al-Si alloys. Owing to undercooling resulted from Sb addition in Al-Si alloys, the refinement structure of eutectic silicon can be achieved.

The temperature and concentration dependences of the surface tension of lithium alloys (up to 33.1 at %) on the basis of a eutectic melt of Pb44.7Bi55.3 are measured in the range from the liquidus temperature to 700 K. The margin of error of the experiments was ~2%. Lithium has a low surface activity in the Pb44.7Bi55.3 eutectic melt, which agrees with the criteria of the surface activity of components in binary liquid metal melts.

The NaCl–KI–K2CrO4 stable triangle was studied by differential thermal analysis. The melting temperature, melt composition, and specific melting enthalpy corresponding to the ternary eutectic were determined in the system. The compositions of crystallizing phases in the eutectic were confirmed by X-ray diffraction.

The aim of the present work was to investigate various means of obtaining a fine eutectic silicon structure in A356.2 alloy and therefore improve the alloy mechanical properties. The effects of solidification rate, Sr modification and melt thermal treatment (MTT) on the silicon particle characteristics of A356.2 (Al–7 %Si–0.4 %Mg) alloy were studied. The particle characteristics measured were the average particle area, average particle length, average particle roundness and average particle aspect ratio, using image analysis and optical microscopy. The results showed that Sr modification-, superheat- and Sr modification-MTT (SrMTT)-processed castings provide fine eutectic Si particles, the SrMTT process giving the best modification results. Both size and morphology of the eutectic silicon particles are affected by the modification process used. The Sr-grain-refined, Sr-melt superheat and SrMTT castings show well-modified fibrous Si particles, whereas the MTT casting exhibits Si particles that, although refined to a certain extent, still retain their acicular morphology. Solidification rate affects the eutectic Si particle size in that a higher solidification rate produces finer Si particles. However, within the range of solidification rates provided by the end-chill mold used in this work, the solidification rate does not affect the morphology of the Si particles.

In this paper we study the formation and behaviour of liquid Al-Ge alloy, its solidification, the resulting microstructures and the appearance of voids in bonded structure for MEMS packaging. The underneath layer influences the wettability of liquid Al-Ge as well as its solidification which can lead to undesirable Al dendrites. Each underneath layer imposes a critical value for the cooling rate above which dendrites are likely to appear. Blanket and patterned Al/Ge deposited wafers are bonded together with process parameters optimized thanks to previous results. The interfaces present a dendritic-free eutectic structure. Micro-voids are observed at the interfaces between Al and Ge phases. The Kirkendall effect and thermal stresses are two possible reasons for voiding phenomenon.

The influence of treating the melts by electromagnetic acoustic fields on the structure and properties of Al–12% Si and Al–20% Si binary alloys is investigated. In the course of experiments, the frequency of the electromagnetic field induced in the loop antenna varies as 500, 1000, and 2000 kHz. The melts are treated after their degassing and refining. It is established that this treatment method of the melts leads to a reduction of the total preparation time of alloy by 12% on average. The short-term treatment of the melts by electromagnetic acoustic fields promotes the refinement of the main phase components of alloys and an increase in their mechanical properties. When treating the Al–12% Si eutectic alloy with a frequency of 500 kHz, α-Al dendrites are refined from 30 to 22 μm and eutectic Si crystals are refined from 13 to 10 μm. When treating the Al–20%Si eutectic alloy with a frequency of 1000 kHz, eutectic Si crystals diminished from 8 to 5 μm and these of primary Si diminished from 90 to 62 μm. The ultimate tensile strength of the Al–12%Si eutectic alloy increases 13% under the mentioned treatment modes, while the relative elongation increases 17%; as for the Al–20% Si eutectic alloy, the same characteristics increases 9 and 65%, respectively. Based on these investigations, it is concluded that the selection of the treatment parameters of the melts of the Al–Si system by electromagnetic acoustic fields should be determined by the silicon content in the alloy. It is necessary to treat the melt by waves with a higher oscillation frequency with an increase in the silicon concentration. This treatment method makes it possible to form the modified fine-crystalline structure of alloy and, consequently, improves their mechanical properties. It can be successfully used when fabricating fine-crystalline foundry alloys and in the production of alloys of the Al–Si system. To determine the optimal treatment parameters depending on the structure of the initial charge and alloy nature, additional investigations are required.

The formation of the excess phase in high-manganese steel is considered over a wide range of cooling rates. This phase, which consists of a phosphide eutectic and secondary carbides, may be deposited both along the grain boundaries and within the grains. At low cooling rates, the phosphide eutectic is mainly formed, with a small quantity of secondary carbides. In addition, excess phase with mixed morphology is encountered. It consists of the eutectic and secondary carbide, with a coherent boundary between them. With increase in the cooling rate, the excess phase consists primarily of secondary carbides; its size is reduced. The influence of the cooling rate on the chemical composition of the excess phase is also of interest. Increase in cooling rate is found to reduce the manganese content in the secondary carbides deposited. The ratio between iron and manganese in the phosphide eutectic does not depend on the cooling rate and is practically constant.

Zr-based bulk metallic glass and copper with different surface roughness were soldered using low temperature eutectic Au–12Ge (wt%) solder on a thermomechanical simulator. The cross-sectional microstructures of the brazed joints were analyzed by scanning electron microscopy (SEM) and transmission electron microscope (TEM) in detail, and the compositional distribution along the interface was analyzed by energy-dispersive spectrometer (EDS). Results show that the surface roughness of base metals plays an important role in the quality of the brazed joint because the surface roughness can enlarge the effective contact area, which can improve the brazing surface quality between two materials. A moderate roughness of treated Zr-based metallic glass of 18 μm is shown to be the best for the soldering, while the surface roughness has a weak effect on the soldering behavior of Au–12Ge solder on copper. After soldering, long-range diffusion of atoms occurs between the base metal and solder, and five distinct regions are formed at the joint region.

Structural transformations during reactions between nickel and an indium–tin eutectic melt are studied via the diffraction of high-energy synchrotron radiation. It is shown that InNi intermetallic compound is the first to form after melting. No phases belonging to a Ni–Sn system are observed. A hypothesis concerning the nanocluster structure of the eutectic melt is proposed: Structural formations with forbidden five-fold, seven-fold, and higher-order rotational axes of symmetry lie at the heart of nanosized clusters.

The equilibrated grain boundary groove shapes of solid CuAl2 in equilibrium with (Al + Cu + Si) eutectic liquid were observed from a quenched sample by using a radial heat flow apparatus. The Gibbs-Thomson coefficient, (solid + liquid) interfacial energy and grain boundary energy of the solid CuAl2 were determined from these observed shapes. The thermal conductivity of the eutectic solid and the thermal conductivity ratio of eutectic liquid to the eutectic solid in the (Al + 26.82 wt.% Cu + 5.27 wt.% Si) eutectic alloy at its eutectic melting temperature were also measured with a radial heat flow apparatus and a Bridgman-type growth apparatus, respectively. The three phases of (Al + Cu + Si) alloy have detected as Al solution, Si and theta (CuAl2) phases with EDX composition analysis and the microstructure of these phases were photographed by SEM. (C) 2016 Elsevier Ltd. All rights reserved.

The properties of the deep eutectic solvent based on choline chloride and levulinic acid, for 1:2 molar ratio, on the (100) surfaces of metals with face centered cubic crystal structures (Ag, Al, and Pt) are studied using classic molecular dynamics simulations. The densification, molecular arrangements and orientations, and electronic density at the metal interfaces are analyzed. Likewise, the dynamic properties of the involved molecules at the metal surfaces are quantified through selfdiffusion coefficients and compared with the behavior in the bulk liquid phases. Strong preferential adsorption at the metal surfaces by the molecules forming the deep eutectic solvents is inferred, which characteristics are analyzed as a function of the type of metal, the strength on metal-solvent interactions, and the changes in the nanoscopic properties of the solvent upon adsorption. The reported results show for the very first time the characteristics of metal-deep eutectic solvent hybrid materials. 2016 American Chemical Society. This work was funded by Qatar National Research Fund, National Priorities Research Program grant (NPRP 6-330-2- 140), Ministerio de Econom?a y Competitividad (Spain, Project CTQ2013-40476-R), and Junta de Castilla y Le?n (Spain, Project BU324U14). We also acknowledge The Foundation of Supercomputing Center of Castile and Le?n (FCSCL, Spain) for providing supercomputing facilities. The statements made herein are solely the responsibility of the authors. Scopus

Freezing and melting of aqueous solutions of alkali halides confined in the cylindrical nanopores of MCM-41 and SBA-15 silica was probed by differential scanning calorimetry (DSC). We find that the confinement-induced shift of the eutectic temperature in the pores can be significantly greater than the shift of the melting temperature of pure water. Greatest shifts of the eutectic temperature are found for salts that crystallize as oligohydrates at the eutectic point. This behavior is explained by the larger fraction of pore volume occupied by salt hydrates as compared to anhydrous salts, on the assumption that precipitated salt constitutes an additional confinement for ice/water in the pores. A model based on this secondary confinement effect gives a good representation of the experimental data. Salt-specific secondary confinement may play a role in a variety of fields, from salt-impregnated advanced adsorbents and catalysts to the thermal weathering of building materials.

Additions of niobium (Nb) and molybdenum (Mo) were made to an Alloy 690 base alloy in order to investigate the formation of a eutectic constituent at the end of solidification and to evaluate the effect of the eutectic liquid on backfilling (or healing) of solidification cracks. Solidification cracking was induced using the cast pin tear test (CPTT) and regions of backfilling were located and characterized via optical and electron microscopy. Computational predictions of fraction eutectic and composition of the eutectic constituent were compared to experimental findings and were found to correlate well in both cases. The extent of crack backfilling increased significantly with increasing Nb content, but the addition of Mo did not seem to influence the amount of eutectic constituent or the degree of backfilling. SEM/EDS analysis confirmed that the eutectic composition is constant and that increasing Nb above 4 wt% has little effect on expanding the solidification temperature range, but has a beneficial effect on mitigating solidification cracking by a crack healing effect.

The tin–bismuth eutectic alloy possesses anomalous physicochemical properties that are dependent on temperature. This paper reports the interfacial reaction and growth behavior of the intermetallic compound (IMC) layer during the dissolution of solid copper in liquid eutectic tin–bismuth at 673–823 K under the influence of the structural transition of liquid eutectic tin–bismuth. The structural transition markedly affected the dissolution rate constant of solid copper and the growth rate of the IMCs. Correspondingly, the application of the liquid structural transition significantly decreased the activation energy of dissolution and increased the apparent activation energy for IMC growth. Moreover, two major roles of elemental Bi on the formation and growth of the IMCs were suggested.

The transition from incomplete to complete grain boundary wetting in copper alloys with 2.2 and 4.9 wt % Co has been studied. These alloys with peritectic phase diagrams differ from previously studied systems with eutectic transformation by the fact that the melt layer separating grains from each other is not enriched, but is depleted by the second component (cobalt in this case). The fraction of completely wetted grain boundaries increases with temperature, as in eutectic systems, from zero at a temperature of 1098°C to ~80% at 1096°C. For symmetric twin boundaries, the temperature dependence of the contact angle with melt drops is constructed. As in the eutectic systems, the contact angle decreases with increasing temperature (although not to zero due to the extremely low energy of symmetric twin boundaries).

The structure and the formation mechanism of brittle eutectic phases and hot cracks formed at grain boundaries were investigated in two Ni-Mo-Cr superalloys with different silicon contents (0.06 and 0.46 wt.%). The eutectic phases and hot cracks can be observed along the rolling direction in the 0.46 wt.% Si heat when heated to 1335 °C or a higher peak temperature up to 1365 °C. Exposure to the higher peak temperatures resulted in the formation of larger eutectic phases and hot cracks in the higher silicon heat. Conversely, there are fewer eutectic phases and smaller hot cracks forming in the low-silicon heat when heated to 1365 °C. The eutectic phases were identified as γ-M6C′ type. Based on the constitutional liquation theory and thermodynamic calculations, it was found that the formation of the eutectic phases and hot cracks is due to the localized melting of primary M6C carbides and surrounding Si-riched matrix. The degree of elements segregation in liquid films determines whether liquid films solidify into eutectic phases or cause hot cracks. This model can reasonably explain the observed phenomena and contribute to designing appropriate solid-solution treatment process and welding procedure to avoid brittle phases and cracks in the Ni-Mo-Cr superalloy. Keywords: Superalloy, Thermodynamic modeling, Carbides, Diffusion, Constitutional liquation

The effect that the Al–Ni eutectic composition has on the microstructure and tensile properties of Al–Zr–V alloys is discussed. It is found that the change in the alloy's solidification behavior brought about by the presence of the eutectic composition mitigates segregation of the zirconium and vanadium atoms, and by doing so it enhances the precipitation hardening characteristics of the alloy and improves its yield strength.

We investigate the atomic structure of aluminum-based alloys both by the X-ray diffraction method and by the reverse Monte-Carlo technique. We compute the total and partial structural factors, the pair correlation functions, and partial coordination numbers. It is shown that Al0.88Si0.12 eutectic melt consists of microregions based on aluminum and an Al–Si solution. Adding nickel to the eutectic leads to the formation of Al–Ni chemically ordered structural regions where nickel is mainly surrounded by aluminum atoms.

Results of electron back-scattered diffraction and transmission electron microscopy studies reveal that the orientation of aluminium in the eutectic phase is different from the surrounding aluminium dendrites and that twin spacing of eutectic silicon increased significantly due to the interaction between strontium and antimony. In addition, the formation of ternary Mg2Sb2Sr intermetallic compound that precedes the eutectic reaction was proposed to be responsible for interaction.

The ternary eutectic system CsF–KF–NaF was studied by differential thermal analysis. The melting point and composition of the ternary eutectic were determined, and so was the boundary of the region of limited series of solid solutions within the composition triangle. The compositions of crystallizing phases were confirmed by X-ray powder diffraction analysis. The specific enthalpy of melting of the ternary eutectic was experimentally found.

Vertically-aligned nanostructures are of interest for novel system-on-a-chip applications including sensing and energy storage. Templated synthesis of such structures has been previously demonstrated via anodized aluminum oxide (AAO). However, the performance of AAO-on-Si devices has been limited by current methods of obtaining well-adhered, thick AAO templates on Si substrates. Thicker AAO templates allow for longer nanostructures of active material, which is expected to increase performance of devices reliant on the surface area or volume of the active material. In this study, Al–Si eutectic bonding is used to achieve thick AAO-on-Si, with templates up to 90 μm thick bonded to the wafer. Carbon nanotubes (CNTs) are grown in the AAO templates bonded to Si to create proof-of-concept on-chip electrochemical double layer capacitors (EDLC) devices. Our devices show a promising value of 0.44 mF cm−2, much higher than previous AAO capacitors on Si chips. The structure of the CNT/AAO/Al/Si stack is examined using SEM and TEM, and the device performance is tested through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GCD) measurements.

In 3D-system packaging technologies, eutectic bonding is the key technology of multilayer chip stacking and vertical interconnection. Optimized from the aspects of the thickness of the electroplated metal layer, the pretreatment of the wafer surface removes the oxide layer, the mutual alignment between the wafers, the temperature of the wafer bonding, the uniformity of pressure and the deviation of the bonding process. Under the pretreatment conditions of plasma treatment and citric acid cleaning, no oxide layer was obtained on the metal surface. Cu/Sn bumps bonded under the condition of 0.135 Mpa, temperature of 280 &deg, C, Sn thickness of 3&ndash, 4 &mu, m and a Cu-thickness of five micrometers. Bonded push crystal strength &ge, 18 kg/cm2, the average contact resistance of the bonding interface is about 3.35 m&Omega, and the bonding yield is 100%. All performance indicators meet and exceed the industry standards.

KOH etching and Au/Si bonding are primarily cost-efficient technologies for the miniaturization and integration of 3D device fabrications. In view of the incompatibility between the conventional Au/bulk Si bonding and KOH etching, a modified Au/bulk Si eutectic bonding structure is proposed and verified in this study. Inspired from the local oxidation of silicon (LOCOS) processes, the Au/Si eutectic reaction interfaces, which are vulnerable in KOH etching, can be protected with the oxide layers by the two-step thermal oxidation processes. Based on IR and SEM&EDS analyses, different etching performances have been dissected at different process parameters, in which choosing two-step oxidation thicknesses plays a critical role. Specifically, the first-step oxidation thickness should be 1.273 times larger than the second-step oxidation while considering the KOH etching ratio of Si to silica. Further, acquired from tensile tests, the average floor levels of bonding strengths (~23 MPa) indicate considerable application potentialities of the modified Au/bulk Si bonding structure in packaging, structure supporting and etc.. Actually, this study provides an analogical strategy for another Si-based eutectic bonding techniques used for wet etching processes.

Full silicon micro electromechanical system (MEMS) accelerometers have advantages of good temperature characteristics, small size, low cost and small package, and become a key component of GNC microsystems. In this work, a wafer level hermetic packaging method of MEMS sandwich accelerometer with three silicon layers is presented. 3D structures on the silicon middle wafer are fabricated by KOH wet etching from both polished wafer surfaces, using the SiO 2 hard mask with thickness steps. The fabrication processes of the cap wafers mainly consist of KOH anisotropic etching, and inductively coupled plasma (ICP) etching. Finally, cap wafers are bonded with the silicon middle wafer by Au-Si eutectic bonding from both sides. The cavity of the sandwich accelerometer encapsulates N 2 with a low pressure of 200Pa. The measurement results show that the closed-loop sensitivity of the proposed accelerometer is 0.575V/g and the zero bias is 0.43g. The −3dB bandwidth of the accelerometer is 278.14Hz. The output stability for 1 hour is 2.23×10−4g (1σ). The output drift of the accelerometer in the full temperature range (−40 to 60°C) is 45.78 mg, and the maximum of the temperature hysteresis is 3.725mg.

Metal wafer bonding is being investigated in industry and research fields due to the relatively low process temperatures (T

The a priori pseudopotential method is employed to propose a model by which phase boundaries form in quasibinary eutectic systems. Interfacial energy for boride and cermet quasibinary eutectic composites, LaB 6 –TiB 2 and LaB 6 –ZrB 2 , is calculated for different temperatures.

The niobium silicide based alloys have been found to be the best alternative over Ni-based superalloys as they provide the balance between both ductility and fracture toughness at low temperature and strength and creep resistance at elevated temperature. The concept of making Nb-silicide based alloys is to form hard silicide phase which is thermodynamically stable and imparts adequate strength to the material at high temperature, within the primary ductile solid solution phase `of niobium. However, the main concern of using these alloys at high temperature is their low oxidation resistance and strength at high temperature. To overcome these limitations, alloying elements can be added, which will improve mechanical properties as well as high temperature oxidation resistance of the alloys. Our present investigation is to study the effect of chromium on the microstructure of Nb–Si hypoeutectic and eutectic alloys. Cylindrical rods of pre-set composition are synthesized by vacuum-arc-melting-cum-suction casting using argon atmosphere. The binary hypoeutectic alloys show the presence of primary (Nb)ss dendrites and lamellar eutectic between (Nb)ss and Nb3Si whereas primary Nb3Si along with eutectic (Nb)ss/Nb3Si are observed in the eutectic binary alloy. In the hypoeutectic Nb–Si–Cr ternary alloys, primary dendritic (Nb)ss, silicide (Nb3Si and/β-Nb5Si3), Laves (Cr2Nb)(depends on chromium concentration) and their eutectic phases are observed whereas Laves phase is found in the microstructure of eutectic Nb–Si–Cr ternary alloys even at very low concentration of Cr (2 at.%). At room temperature, compressive properties of these rods have been reported.

In this work, various amounts of Bi element have been added to the eutectic Pb-Sb to form bearing- solder materials. The Pb-Sb eutectic has been produced by rapid solidification using melt spinning technique with various amounts of Bi have been added to it, in the ratio 1, 2 , 3, 4, and 5 wt.%. Scanning electron microscopy (SEM), X- ray diffraction (XRD) analysis and differential scanning calorimetry (DSC) have been carried out. Microhardness measurements were also carried out using Vicker’s hardness technique. The results showed that, the ternary alloys up to 4 wt.% Bi have properties superior to binary eutectic material.  Bismuth up to 4wt. % increases the Young’s modulus, Vicker’s hardness and decreases the electrical resistivity, internal friction and melting point. The ternary Pb-13.1Sb-4Bi solder alloy has a lower melting point about 237.87 ˚C. Also, the results show that formation of Bi phase developed the mechanical properties and Vicker’s hardness due to addition of Bi element.  The addition of Bi refines the crystal size of Sn in case of melt spun alloys as seen in scanning electron micrographs and X-ray diffraction.

Die attachment quality plays a remarkable role in producing highly reliable solid-state lighting fixtures by providing a dominant impact on thermal resistance. Color rendering, efficacy, and lifetime are strongly related to junction temperature. This paper investigated the effects of varying the thickness of sputter-coated copper on an Al2O3 ceramic substrate on the thermal resistance and luminous intensity of flip-chip light-emitting diode (LED) devices. Eutectic bonding was applied to provide excellent bonding strength and low void content between the chip and ceramic substrate. The thermal resistance dramatically decreased as the copper thickness was reduced because of a substantial reduction in the conduction impedance for heat dissipation from the junction to the ambient. The luminous intensity was improved by reducing the copper thickness as the driving current was increased from 50 to 700 mA. The results demonstrated that reducing the copper thickness effectively reduced the junction temperature and improved the performance of the eutectic flip-chip bonding LED devices.

Deep eutectic solvents are a new generation of solvents formed by the combination of an ionic compound with an hydrogen bond donor, which leads to a low temperature melting mixture. This work reports a Density Functional Theory study combined with a topological analysis of the electronic density for deep eutectic solvents to rationalize melting temperature at the molecular level. The reported results show a direct relationship between the melting temperature and the hydrogen bond network features. The proposed methodology shows the feasibility of tailoring macroscopic properties of deep eutectic solvents through the molecular structure of involved compounds.

The structural, morphological, and chemical characteristics of aluminum-copper alloys before and after contact with the liquid Ga-In eutectic have been studied. X-ray diffraction (XRD) analysis has revealed that alloying results in the formation of Al9Cu11.5 and Al2Cu intermetallic compounds and CuAl0.005, CuAl0.14, and AlCu0.004 substitutional solid solutions. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have shown that, for the CuAl0.005 and CuAl0.14 substitutional solid solutions of aluminum in copper and the individual Al9Cu11.5 intermetallic compound in contact with the liquid Ga-In eutectic, surface spreading of the eutectic without any significant morphological and chemical changes in the studied systems is observed. At the same time, the alloy containing the Al2Cu intermetallic compound and the phase of the AlCu0.004 substitutional solid solution of copper in aluminum interacts with liquid Ga-In eutectic owing to the activation of aluminum as a solid solution component. This activated Al-Cu alloy reacts with liquid tert-butyl chloride in the presence of ethylene to form catalyst Al-Cu-Cl complexes in situ. It has been speculated that these complexes are mostly formed owing to the dissolution of the phase of the AlCu0.004 substitutional solid solution of copper in aluminum in a medium of liquid tert-butyl chloride.

Sn–Cu eutectic modified by minor In, Cr and Ni additions are one of the major alternatives to lead-free solders. The results show that nanostructured solders produced by rapid solidification are dependent on melting properties and the melting temperature. It is found that the In, Cr or Ni addition has the effect of suppressing the formation of eutectic rapidly solidified Sn–0.7Cu alloy. The results indicated that the melting temperatures (Tm) of Sn–0.7Cu are modified to lower temperature by In, Cr and Ni additions. The formation of new intermetallic compounds such as In3Sn, Cu6Sn5, Cu10Sn3, and NiSn are more uniformly distributed inside Sn-rich phase effectively enhancing the hardness and creep resistance of the eutectic Sn–0.7Cu solder joint at room temperature. The results of these tests are consistent with positive effect of the In, Cr and Ni in enhancing the performance of the eutectic Sn–0.7Cu solder as a practical to lead-free solder.

Eutectic materials are widely used in high-temperature and high-reliability applications due to their excellent thermal and mechanical properties compared with other bonding materials. However, the high bonding temperature and high yield strength of eutectic materials can also cause some reliability issues during the die bonding process, such as die cracking and fly die. The fly die issue, which refers to the phenomenon of silicon die flying away from the bond pad after the collet moves away, is thoroughly studied in this paper. This paper emphasizes the following two aspects: 1) evaluation of the bonding strength when fly die happens and 2) finding out the driving forces for this phenomenon. It was found out that the expansion of trapped air in the bondline cavity is the key driving force. As the eutectic die bonding temperature is usually very high, the trapped air will expand and generate high pressure. Meanwhile, the eutectic alloy is still in liquid state when the collet moves away, which results in a weak bonding strength. When the potential energy stored in the trapped air breaks the weak bonding of the liquid eutectic, the die will fly away. Fly die most possibly takes place when the wetting area is less than 18% of the overall die bottom surface according to thermodynamic calculation. This theory was supported by both experimental observations and computational fluid dynamic simulations. Optimization methods were finally proposed to reduce die flying risk based on the knowledge obtained.

Eutectic compounds play an important role in the fabrication and packaging of devices with low thermal budgets. Taking low-cost polymers into account, eutectic soldering and eutectic bonding temperatures below the glass transition temperature of the aforementioned polymers, 150 °C and below, need to be met. In this regard, thermocompressive eutectic bonding processes of silicon integrated circuits by means of the binary eutectic compounds indium–tin and indium–bismuth were optimized with regard to least necessary thermal energy, and the feasibility thereof onto polycarbonate and poly(methyl methacrylate) substrates was investigated.

In this work, Au–Sn eutectic bonding and Au–Sn thermo-compression bonding are studied for applications in hermetic packaging at wafer level. Eutectic bonding experiments were performed under vacuum or pure nitrogen at temperatures between 310 and 400 °C while thermo-compression bonding experiments were performed under vacuum at 270 °C. Nickel layers 350 nm thick are used as wetting layers on both cap and device sides. During these experiments, the interaction of electrodeposited Au–Sn alloy with nickel layers is studied either in solid or liquid state. The diffusion paths at 270 °C as well as during isothermal solidification of the joint at 310, 350 and 400 °C are determined in relation with the thicknesses of the reaction layers formed at the interfaces and the microstructure of the joint. The effective interdiffusion coefficient in the ζ-Au5Sn phase is deduced at 270 and 310 °C. Moreover, the melting and solidification process of electrodeposited Au/Sn layers with an overall eutectic composition were studied by Differential Scanning Calorimetry in a specific configuration that does not involve the interaction of Au–Sn alloy with the nickel layer. Bonded wafers with good mechanical properties were characterized by cross-section Scanning Electron Microscopy using Energy Dispersive X-ray mode. The mechanical strength of the seal was checked by blade plate insertion technique.