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Irradiation of the molten eutectic Bi43Sn57 alloy with ultrasonic energy produced different bismuthtin phases that were not reported in the equilibrium binary phase diagram. The X-ray powder diffraction data, refined using the Rietveld method, allowed the identification of these metastable phases and their crystal structure. The Bi2Sn and β′-Sn phases, with distorted β-Sn type structure, were obtained in the sample which was rapidly quenched after ultrasonication. On the other hand, the equiatomic phase BiSn was obtained in the quenched sample when the ultrasonication was continued during the rapid cooling below the eutectic point. The ultrasonicated samples were characterized by differential scanning calorimetry. The results suggested that the metastable phases, which were kinetically stable at RT, decomposed into equilibrium components during the heating treatment at 320 °C, and that this conversion is an irreversible process. Observations by scanning electron microscopy and energy dispersive X-ray analysis complete the characterization of samples.

NiTi wires were brazed together via liquid eutectic formation between NiTi and Nb powders deposited at the wire contact region. The brazed region shows proeutectic NiTi(Nb) in contact with the wires, sandwiching a NiTi-Nb eutectic structure, whose microhardness and stiffness, as characterized via nanoindentation, are higher than the NiTi wires, while also showing signs of high ductility. NiTi-Nb eutectic bonding may thus be a viable approach for producing shape-memory NiTi scaffolds brazed from stacked, woven, or braided wires.

We present the thermophysical properties and eutectic growth of undercooled liquid Zr91.2Si8.8 alloy at electrostatic levitation state. The obtained maximum undercooling is 371 K, which reaches up to 0.2TE. The density of liquid alloy decreases linearly with increasing temperature. The ratio of specific heat to emissivity is measured and the specific heat is derived accordingly. The solidification microstructure is composed of αZr and Zr3Si phases and displays a transition from lamellar eutectic to anomalous eutectic with the enhancement of undercooling. The growth velocity of lamellar eutectic is measured to be only 1 mm/s, whereas it increased to 90 mm/s for anomalous eutectic.

Al–5 wt.% Si-based alloys with 0.05 wt.% Eu addition were produced by controlled sand-casting and melt-spinning, respectively. The modification of eutectic Si caused by 0.05 wt.% Eu addition was investigated by thermal analysis, differential scanning calorimetry and multi-scale microstructure characterization techniques. In the case of controlled sand-casting, 0.05 wt.% Eu addition was found to modify the eutectic Si into a fibrous morphology. Multiply twinned Si particles were observed within eutectic Si. Furthermore, the Al 2 Si 2 Eu phase was also observed both in the vicinity of eutectic Si and within eutectic Si, which was believed to hinder Si growth. In the case of melt-spun samples, nanometer-sized Al 2 Si 2 Eu phases were observed. However, after controlled cooling in a differential scanning calorimeter, multiply twinned Si particles were observed. The formation of multiply twinned Si particles was attributed to the adsorption of Eu atoms along the 〈1 1 2〉 Si growth direction of Si and at the intersection of two {1 1 1} Si facets. Twinning was observed in both fundamentally different casting processes: controlled sand-casting and melt-spinning. This is fully consistent with the well-known poisoning of the twin plane re-entrant edge and the impurity-induced twinning modification mechanisms.

In this paper, the microstructure and thermal behavior of two rapidly solidified of eutectic Indium-Bismuth and Indium-Bismuth-Tin Field’s metal are reported. This work experimentally measures the specific heat of the eutectic alloys of the binary Indium-bismuth and indium –bismuth –tin tertiary system using a differential scanning calorimeter (DSC) technique and analyzes the results to determine the thermodynamic properties of the system have sufficient scaling for experimental modeling applications. The resultant ribbons were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) techniques, energy dispersive x-ray (EDX) technique. From the differential scanning calorimetry measurements, it is found that entropy change, enthalpy and specific heat are improved and enhanced compared with literature. The electrical resistivity was reported for temperatures between 295 and 330 K for all the melt-quenched ribbons of binary In-49Biand tertiary In-32.5 Bi -16.5 Sn (wt.%). The microhardness, elastic moduli, internal friction and both thermal diffusivity and thermal effusivity were also measured. Field’s metal is more than suitable for use in experimental settings as it is non-reactive, non-toxic, simple to manufacture, easy to use, and responds to a magnetic force.

Phase diagram of o-nitroaniline–α-naphthol system has been investigated by thaw melt method and results showed the formation of a simple eutectic mixture. The values of the heat of fusion of components and eutectic mixture were determined with the help of DSC technique. Excess Gibb’s free energy (GE), excess entropy (SE) and excess enthalpy (HE) of mixing were calculated. In order to know the nature of interaction between the two components, FT–IR spectral studies were made. The modulus of rupture of the pure components and the eutectic mixture were determined. The isotropic as well as the anisotropic solidification behavior were studied. Microstructural studies of o-nitroaniline showed the formation of lamellar with leafy like and α-naphthol showed the formation of broken rock like microstructures, whereas in the eutectic mixture, growth of flat crystals in different directions from a particular point were seen. Undercooling measurements were made. Optimized geometrical parameters, molecular properties and potential energy of the interacting molecules of the eutectic mixture have been examined using various computational methods.

The formation mechanism ofAl2O3-HfO2eutectic structure, the preparation method, and the formation mechanism of the eutectic EBC layer on the silicon carbide substrate are summarized.Al2O3-HfO2eutectic EBC film is prepared by optical zone melting method on the silicon carbide substrate. At high temperature, a small amount of silicon carbide decomposed into silicon and carbon. The components ofAl2O3andHfO2in molten phase also react with the free carbon. TheAl2O3phase reacts with free carbon and vapor species of AlO phase is formed. The composition of the molten phase becomesHfO2rich from the eutectic composition.HfO2phase also reacts with the free carbon and HfC phase is formed on the silicon carbide substrate; then a high density intermediate layer is formed. The adhesion between the intermediate layer and the substrate is excellent by an anchor effect. When the solidification process finished before all ofHfO2phase is reduced to HfC phase, HfC-HfO2functionally graded layer is formed on the silicon carbide substrate and theAl2O3-HfO2eutectic structure grows from the top of the intermediate layer.

This work highlights a new bonding technique for micro-fabrication of an all silicon 3 meter gas chromatography column that could withstand the temperature cycling required for axial temperature programming. Proper separation of a complex gas mixture using a miniaturized GC column is critical in improving the overall performance of a lab on a chip system for environmental monitoring, medical diagnoses, and gas impurity measurement. To improve upon current methodology the column was first fabricated using micro-fabrication processes; experimentally validated using a high performance 3 meter GC column coated with OV-1 stationary phase. This process demonstrates that the bonding quality of the GC column to a 200 μm thick silicon lid was improved when using a new gold eutectic bonding technique. Furthermore, a new quality control technique was developed in order to test the overall bonding quality of the bonded pieces by fixing the bottom column and applying a mechanical shear force to the top lid. This method could ultimately be used for quality control of each individual bonded columns. The gold bonded interface of the gold diffusion bonded area is further characterized using surface analysis. In the end, the utility of the column was demonstrated by separating 21 organic compounds with different Kovats retention index and molecular weights in less than five minutes. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0031510jss] All rights reserved.

Al-5 wt pct Si-based alloys with Na additions (19 and 160 ppm) have been produced by controlled sand casting and melt spinning. Entrained droplet technique and differential scanning calorimetry were employed to investigate the nucleation behavior of eutectic Si. High-resolution transmission electron microscopy and atom probe tomography were used to investigate the distribution of Na atoms within eutectic Si and at the interfaces between eutectic Si and eutectic Al. It was found that (i) only 19 ppm Na addition results into a high undercooling (49 K (49 °C)) of the entrained eutectic droplet. However, further increasing Na addition up to 160 ppm exerts no positive effect on the nucleation of eutectic Si, instead a decreased undercooling (29 K (29 °C)) was observed. (ii) Na addition suppresses the growth of eutectic Si due to the Na segregation at the interface between eutectic Si and eutectic Al, and (iii) Na addition promotes significant multiple Si twins, which can be attributed to the proposed adsorption of Na atoms at the intersection of Si twins and along the 〈112〉Si growth direction of Si. The present investigation demonstrates, for the first time, a direct observation on the distribution of Na atoms within eutectic Si and thereby provides strong experimental supports to the well-accepted impurity-induced twinning growth mechanism and poisoning of the twin plane re-entrant edge growth mechanism.

In this paper, we present a novel design of tri-axis gyroscope which consists of two diagonal-pendulum masses for lateral sensing, coupled with and enclosed in a traditional tuning fork driving frame. The diagonal-pendulums are driven to swing via tilted transforming beams as the driving frame oscillated in plane, and rotate around their torsional beam out-of-plane as orthogonal lateral angular rate applied. The symmetric arrangement of whole structure lowers mechanical complexity and the sensing way of "one diagonal-pendulum for one lateral axis" eliminates sensing proof mass sharing which can effectively suppress the cross-talk effect. The prototype device has been successfully fabricated by using SOI-based bulk micromachining processes and vacuum packaged by Al---Ge eutectic bonding. The sensitivities for three axes are 4.83, 1.47 and 1.38 mV/(°/s), respectively, with nonlinearity of less 1 % and bandwidth of above 600 Hz.

This paper describes the investigation of a microdischarge-based approach for sensing the diaphragm deflec- tion in a monolithically fabricated pressure sensor. This transduc- tion approach is appealing from the viewpoint of miniaturization. The device consists of a deflecting Si diaphragm with a sensing cathode, and a glass substrate with an anode and a reference cath- ode. The total exterior volume of the device is 0.05 mm 3 ; typical electrode size and separations are 35 and 10 µm. Pulsed microdis- charges are initiated in a sealed chamber formed between Si and glass chips, and are filled with Ar gas. External pressure deflects the Si diaphragm and changes the interelectrode spacing, thereby redistributing the current between the anode and two competing cathodes. The differential current is indicative of the diaphragm deflection which is determined by the external pressure. A 6-mask microfabrication process is investigated for device fabrication. Electrode connections to the interior of the chamber are provided by laser drilling and copper electroplating through high aspect ratio glass vias. The Si and glass substrates are bonded by Au-In eutectic. The redistribution of plasma current between competing cathodes, as a consequence of diaphragm deflection over a range of pressure, was experimentally demonstrated. First principles modeling of transient microdischarges have provided insights to the fundamental processes responsible for the differential current and guidance for scaling the device to smaller dimension. (2013-0200)

Metallic copper, which has low electrical resistivity and high thermal conductivity, is widely used as an interconnector or substrate within microelectronic packages. If a small amount of oxygen is introduced to the surface of the copper, a eutectic liquid forms above 1065 °C. The eutectic liquid wets many ceramics well; it is thus possible to bond slightly oxidized copper to many ceramics directly. The present report summarizes previous results on three systems, Al2O3/Cu, AlN/Cu, and Si3N4/Cu laminates, prepared by the eutectic bonding process. The reported data demonstrate that ceramic/copper interfaces prepared with this technique are strong. Though little attention has been paid to the thermal characteristics of ceramic/copper laminates, the limited data suggest that the thermal conductivity of the laminates is high, the potential for using the laminates for thermal dissipation is thus high. In the present report, the current status for the technique is summarized; critical topics for further improvement are also proposed.

A liquid–metal quenching method is designed for studying the rapid solidification behavior of oxide eutectic composites. The lamellar spacing of an Al2O3/Y3Al5O12 eutectic nanocomposite processed using this method is only 50 nm, which is an order of magnitude smaller than that reported previously. Results from the microstructural characterization of the resulting materials are described. Using the classical eutectic growth model, the relative solidification rate in this method is calculated to be 1.88 × 10−2 m s−1.

Direct bond copper (DBC), also called the gas-metal eutectic bonding method, is an important substrate material commonly used for thermal and electrical management in power modules. Developed almost 40 years ago by General Electric, there is wide use of this structure when there is a need of a substrate with high current-carrying and high thermal conductive abilities. The components of DBC are a ceramic (usually aluminum oxide (Al2O3) also called alumina) and a bond piece of copper on one or both sides. This copper is strongly bond to the alumina giving strong adhesion and combining benefits from both materials. This paper will give a summary of DBC technology and will discuss the role that furnace temperature and atmosphere perform during processing.

In this work, a particular ultra-thin buffer layer (UBL) with various thickness ranging from 10 nm to 100 nm and different materials including Co, Ni, Pd and Ti is inserted between Cu/Sn to delay the interdiffusion prior to eutectic bonding. The efficacy of the buffer layer and the bonding quality are systematically conferred using microstructure imaging, material analysis, and electrical performance. In addition to symmetric Cu/Sn bonding with UBL, an asymmetric Cu/Sn-Cu bonding which is proposed to relieve the heat-enhanced interdiffusion issues thereby enhancing the reliability performance is demonstrated with the assistance of UBL technology.

This paper demonstrates integration non-destructive analysis tools solution of MEMS multi-bonding to inspect the fusion bonding interface and eutectic bonding interface to locate defect layers. This analytical study shows successful SAT (Scanning Acoustic Tomography) and IROM (Infrared Optical microscopy) inspection of MEMS multi-bonding single issue layer. The multi-bonding double layers were happened issue simply addition cross-section to verify.

This paper investigated the bonding shear strength of eutectic-based wafer-level-packaging (WLP) for piezoresistive MEMS accelerometers. The bonding conditions were experimentally and analytically determined to realize higher shear strength without a diffusion of the solder material atoms to the adhesion layers: the energy dispersive X-ray (EDX) spectrometry and molecular dynamics (MD) simulations clarified the eutectic reaction of solder materials used in this research. Consequently, the bonding load of 9.8 kN and the temperature of 300 °C was found to be one of rational conditions because of a sufficient shear strength to endure the polishing process after the WLP and few diffusion of solder material atoms to the adhesion layer.

A monolithic piezoelectric Aluminum Nitride (AlN) MEMS-CMOS microphone for high-sensitivity, low-power applications is presented. The MEMS microphone that is directly bonded to a CMOS buffer for current-to-voltage conversion consists of a circular-shaped AlN-SiO2 unimorph membrane. The radius, package dimensions, and electrode layout were optimized to maximize the MEMS sensitivity. The integrated device was fabricated by wafer-scale eutectic bonding of a 0.18 μm CMOS buffer to the MEMS microphone. In this work, the piezoelectric microphone is formed by 1 μm-thick AlN and 1 μm-thick SiO2 layers and provides an average off-resonance sensitivity of 0.68 mV/Pa, a resonance frequency of 11.2 kHz, and a floor noise of 0.03 μV/Hz.

Au/Si eutectic bonding is considered to BE a promising technology for creating 3D structures and hermetic packaging in micro-electro-mechanical system (MEMS) devices. However, it suffers from the problems of a non-uniform bonding interface and complex processes for the interconnection of metal wires. This paper presents a novel Au/Si eutectic wafer bonding structure and an implementation method for MEMS accelerometer packaging. The related processing parameters influencing the Au/Si eutectic bonding quality were widely investigated. It was found that a high temperature of 400 °C with a low heating/cooling rate of 5 °C/min is crucial for successful Au/Si eutectic bonding. High contact force is beneficial for bonding uniformity, but the bonding strength and bonding yield decrease when the contact force increases from 3000 to 5000 N due to the metal squeezing out of the interface. The application of TiW as an adhesion layer on a glass substrate, compared with a commonly used Cr or Ti layer, significantly improves the bonding quality. The bonding strength is higher than 50 MPa, and the bonding yield is above 90% for the presented Au/Si eutectic bonding. Furthermore, the wafer-level vacuum packaging of the MEMS accelerometer was achieved based on Au/Si eutectic bonding and anodic bonding with one process. Testing results show a nonlinearity of 0.91% and a sensitivity of 1.06 V/g for the MEMS accelerometer. This Au/Si eutectic bonding process can be applied to the development of reliable, low-temperature, low-cost fabrication and hermetic packaging for MEMS devices.

A low temperature and low pressure fluxless bonding of plateless Cu-Cu substrates has been achieved by transient liquid phase sintering of Ag and Sn-Bi eutectic powder mixture in a formic acid reducing environment. The effects of Sn-Bi addition amount and sintering temperature to the shear strength and microstructure were investigated. Remelting temperature of the sintered paste was also examined. Shear strength of 30 weight percentage added Sn-Bi that was sintered at 250°C was over than 20 MPa. The microstructure varied with the Sn-Bi addition amount, however, mainly consisted of Ag solid solution and/or Ag-Sn intermetallic compounds (IMCs), Bi-rich phase and Cu-Sn IMCs. No remelting event at Sn-Bi eutectic temperature was observed and the remelting temperature shifted to approximately 262°C, implying the possibility for higher operation temperature although the processing was performed at lower temperature.

This paper presents the development of Al-Ge eutectic bonding for wafer level chip scale packaging of MEMS sensors. Al is sputtered on the MEMS wafer while an Al/Ti/Ge stack is sputtered on the cap wafer. The bonding temperature and bonding time are 430°C and 30min, respectively. A CMOS compatible Ti/Ni stack was deposited as getter on the cap wafer to maintain the vacuum level inside the cavity. A silicon pirani gauge was used as hermeticity indicator to evaluate the vacuum level of the bonding. The operational dynamic range of the pirani gauge is 100mTorr-76Torr. The experimental results over three wafers show that the achieved vacuum level of the bonding is less than 200mTorr with yield more than 90%, 1000 rapid thermal cycles from -50°C to 150°C with 1 hour for each cycle were conducted, and the related vacuum level were recorded at 150th, 400th, 650th, 800th, 1000th cycle. The normalized vacuum degradation percentage are about 1.6%, 2.05%, 2.25%, 2.54%, 2.78%, 2.82%, respectively. The results also show the vacuum level trends to be stable from the 650th cycle.

In this study, a low temperature solid state diffusion bonding process with (111) highly oriented nano-twined Cu (nt-Cu) was proposed. A less void bonding interface was observed reveals a good bonding quality for the bonded samples. In addition, a large quasi-single grain was identified in the bondedfilm. Based on these results, it is believed that high strength and durable bonding structure can be accomplished by bonding two highly (111)-oriented nt-Cu films.

This paper reports on the successful implementation of a wafer-level vacuum-packaged, CMOS-compatible aluminum nitride (AlN) based microelectromechanical system (MEMS) energy harvester (EH). The reported EH features high Q-factor (709.3) and high-g survivability (harmonic at 20g), achieved through wafer-level vacuum-package scheme which reduces the air damping effect and increases the Q-factor, overcoming the tradeoff between vibration amplitude and output power density for EHs operated in air. A power of 468.77µW, bandwidth of 71Hz (3.66%) is delivered by a ~0.119cm3 footprint (1×0.7×0.1705cm3) EH at 20g sinusoidal input vibration, equates to a record power density of ~3.93mW/cm3. This novel packaging and design scheme, which utilizes two-step three-wafer wafer level eutectic bonding, allows size reduction and shock-resilience improvement of future EH. The ability to harvest broad spectrum mechanical vibration energy with small footprint and high-g survivability, makes the reported EH one step closer towards powering the next generation battery-less Smart Tire Pressure Monitoring System (TPMS). Furthermore, the whole integration process, including the wafer-level vacuum-packaging process, is CMOS compatible, making the reported EH viable for mass production with low fabrication cost.

Low temperature bonding of Au-electroplated Cu and Cu electrodes with Sn-57Bi-1Ag solder was examined. Longer bonding time gave a Au/Cu joint higher melting point. In the joint bonded at 170 °C for 1 min, a large scallop-shaped AuSn 4 layer formed in the joint interface of Au and solder. A Au-diffused layer formed in the tip of the AuSn 4 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 s-Sn and Bi and the Au layer disappeared. As the result, the solder area changed from the eutectic microstructure to Bi phases including AuSn 4 and Ag 3 Sn phases in the bonding time over 30 min. The bond strength of the joint decreased with increasing the bonding time due to the fracture mode change. Aging treatment gave the effect same as increasing bonding time on melting properties and bond strength of the joint.

The microstructure of melt extracted Ti-44Al-8Nb-0.2W-0.2B-1.5Si fiber were investigated. When the rotation speed increased from 2000 to 2600 r/min, the appearance of the wire was uniform with no Rayleigh-wave default. The structure was mainly composed of fine α2 (α) phase dendritic crystal and a second phase between dendrite arms and grain boundaries. The precipitated second phases were confirmed to be Ti5Si3 from the eutectic reaction L→Ti5Si3 + α and TiB. As the lower content of Si and higher cooling rate, a divorced eutectic microstructure was obtained. Segregation of Ti, Nb, B, Si, and Al occurred during rapid solidification.

Aiming to develop high-strength Al-based alloys with high material index (strength/density) for structural application, this article reports a new class of multiphase Al alloys in the Al-Ni-Cr system that possess impressive room temperature and elevated temperature (>= 200 degrees C) mechanical properties. The ternary eutectic and near eutectic alloys display a complex microstructure containing intermetallic phases displaying hierarchically arranged plate and rod morphologies that exhibit extraordinary mechanical properties. The yield strengths achieved at room temperatures are in excess of 350 MPa with compressive plastic strains of more than 30 pct (without fracturing) for these alloys. The stability of the complex microstructure also leads to a yield stress of 191 +/- 8 to 232 +/- 5 MPa at 250 degrees C. It is argued that the alloys derive their high strength and impressive plasticity through synergic effects of refined nanoeutectics of two different morphologies forming a core shell type of architecture. (C) The Minerals, Metals & Materials Society and ASM International 2017

Ultrasonic fingerprint sensors based on micromachined ultrasound transducers require very fine pitch to achieve high resolution imaging. We investigate a 110×56 PMUT array based on monolithic eutectic bonding to CMOS. To achieve high fill-factor, the PMUTs are anchored through small eutectic pillars, resulting in a high degree of mutual coupling between neighboring PMUTs. As a result, the mode shape is more complicated than a single-MUT dynamic model. We created a finite element model that better models the mode shapes exhibited by the entire array. Experimental measurement of the mode-shape via laser Doppler vibrometry allows us to compute the volume velocity, which correlates to the measured far field pressure.

Gas-free combustion processes are accompanied by the appearance of a liquid phase in the reaction front. The role of contact eutectic alloys in the combustion wave was studied during combustion of the Ti, B, and Fe powders. Analysis of the temperature profiles in the combustion wave of the Ti-B-Fe system with different Fe content showed that the eutectic melts could be formed both in the Stefan mode and in the chemical conversion mode. Conducting the combustion process in the presence of a certain eutectic allowed us to control the structure of the combustion zone and the regularities of propagation.

A high performance aluminum nitride (AlN) on silicon piezoelectric resonator is reported in this paper. The resonator is fabricated based on the AlN on cavity-silicon-on-insulator (SOI) platform and vacuum encapsulated using the wafer level chip scale packaging (WLCSP) via aluminum-germanium (Al-Ge) eutectic bonding approach. After dicing, the resonator has an attractive compact size of 0.6×0.6×0.7 mm3. The fabricated resonator achieves a quality factor (Q) of 9517 and an impedance of 51 Ohm at its resonant frequency of 27.19 MHz. The measured frequency drift is within 30 ppm after 1000 thermal cycles (−45 °C to 85 °C). No obvious impedance change caused by the thermal cycles is observed. The piezoelectric resonator based programmable oscillator shows an overall frequency drift of 3 ppm over the temperature range of −20 °C to 70 °C, thanks to the passive and active temperature compensation approaches. With this stable frequency reference, the programmable oscillator produces a 76.4 MHz frequency output with an integrated phase jitter of 2.21ps from 12 kHz to 10 MHz.

Diffusion couples of pure gold and pure tin were created by mechanical cold rolling method. The couples were isothermally treated at temperatures slightly above and below the eutectic temperature near tin-rich region of the equilibrium phase diagram. Differences in the diffusion behaviors were observed as a function of treatment temperatures below (473 K) and above (498 K) the eutectic temperature. At the boundary, it was found that first solid state inter-diffusion was initiated which resulted in local compositional change and solid-state formation of intermetallic compounds. As the composition shifts away towards mixing, the growth of the intermetallic phases was monitored as a function of temperature and time. At temperature above the eutectic, there may be a liquid fraction as the interface isothermally melted. The kinetic involves dissolution of Au atoms into locallized tin-rich liquid. At below eutectic temperature, the formation and growth kinetic of phases follows a solid state diffusion mechanism. By investigation the exponent n values in the growth equation l = k(t/t0)n, the values were found to be in between 0.62 - 0.77 which implies that the kinetics of IMC formations experiment are controlled by both diffusion and intermetallic reaction. The bonding temperature was found to be faster and more reliable at bonding temperature slightly above the eutectic.

As a major step in the conduction of heat dissipation, wafer bonding significantly contributes to device reliability. This work presents the Cu–Sn eutectic bonding with a Mo buffer layer for light emitting diodes to increase its reliability. The conventional Ag-paste bonding and Cu–Sn bonding (without Mo top layer) are also studied for comparison. Their reliability is measured using thermal shock treatments ranging from − 40 to 120 °C (200 cycles). Experimental results indicate that the eutectic bonding with a Mo buffer layer demonstrates a better device performance than the other two counterparts. Following thermal shock treatment, the light droops for the Ag-paste, Cu–Sn, and Mo/Cu–Sn bonding samples are 15, 11 and 7%, respectively. Additionally, the increasing ratios of thermal resistance are 26, 33 and 19%, respectively. Moreover, adding the Mo buffer layer can relieve the thermal stress problem, owing to the thermal expansion mismatch in Gallium–Nitride/Cu–Sn/submount wafer bonding structures.

In this paper we investigate chip bonding technology of GaAs/AlGaAs quantum cascade lasers (QCLs). Its results have strong influence on final performance of devices and are essential for achieving room temperature operation. Various solders were investigated and compared in terms of their thermal resistance and induced stress. The spatially resolved photoluminescence technique has been applied for a device thermal analysis. The soldering quality was also investigated by means of a scanning acoustic microscopy. The particular attention has been paid to Au–Au die bonding, which seems to be a promising alternative to the choice between hard and soft solder bonding of GaAs/AlGaAs QCLs operating from cryogenic temperatures up to room temperatures. A good quality direct Au–Au bonding was achieved for bonding parameters comparable with the ones typical for AuSn eutectic bonding process. High performance room temperature operation of GaAs/AlGaAs QCLs has been achieved with the state-of-the-art parameters.

In this work, a low-temperature eutectic bonding process based on the formation of an indium (In)-tin (Sn) alloy is studied at temperatures below 200 °C. The formation of the In-Sn alloy is investigated through a secondary ion mass spectroscopy (SIMS) depth profiling analysis, and the quality of the bonding region is evaluated by using cross-sectional scanning electron microscope(SEM) and shearing force measurements. At 170 °C, which is above the melting temperature of In (156 °C), a large amount of In-Sn alloy is formed without the assistance of any flux owing to the expanded eutectic composite range and the improved quality of the In-Sn contact, resulting in a higher bonding strength (205 N). The obtained results show the feasibility of using a low-temperature fluxless bonding process for the fabrication of upper-level devices in monolithic three-dimensional integrated circuits (3D-ICs).

Ni foil is used as interlayer to join Zircaloy-4 by transient liquid phase bonding. The Zoneβ→α is formed in the joints and its width increases with temperature. The formation of Zoneβ→α is controlled by both bonding temperature and Ni concentration. The Zoneβ→α is mainly composed of primary Zr phase and eutectic Zr(Zr2Ni) structure. The micro-hardness of the joints mainly depends on the precipitates and the size of α-Zr phase. The non-planar bonding interfaces are developed in the joints when the bonding temperature above 960 °C. Resulting from the non-planar bonding interfaces, the maximum shear strength of the joints is 358 ± 19 MPa.

Al–Cu alloys of compositions near eutectic point [hypoeutectic (Al–19Cu), eutectic (Al–33Cu) and hypereutectic (Al–35·5Cu) and (Al–36Cu)] were chemically modified by adding 0·6 wt-%Al–Ti5–B1 master alloy. In addition, the specimens of unmodified and chemically modified eutectic alloy were heat treated at 500°C for different holding times (4, 24, 48 and 72 h for the unmodified and 4 and 29 h for the modified ones) followed by water quenching. The structure of chemically treated alloy was changed from large dendrites to fine rosette shaped α-Al grains inside fine eutectic matrix. For these alloys, the liquid–solid transformation temperature was shifted to a higher value. The addition of Al–Ti5–B1 master alloy to the eutectic (Al–33Cu) alloy transforms it into hypoeutectic one of fine lamellar eutectic structure. The chemically treated hypereutectic alloy (Al–35%5Cu) was changed into full eutectic alloy.

Containerless solidification of hypoeutectic Al–50%Ge and eutectic Al–51.6%Ge alloys has been carried out with an ultrasonic levitator. The undercooling of the two alloys achieves 112 K(0.16 T L ) and 95 K(0.14 T E ), respectively. In both of these alloys, (Al) phase always nucleates and grows primarily in Al–51.6%Ge eutectic alloy at small undercoolings. When the undercooling is larger than 80 K, competitive nucleation between (Al) and (Ge) phases occur and (Ge) solid solution can nucleate as primary phase. The (Al)+(Ge) eutectic composed of branched (Ge) phase and interspacing (Al) phase is much refined under ultrasonic levitation condition. Divorced eutectic of the two phases is obtained near the surface of acoustically levitated Al–50%Ge hypoeutectic alloy.

Computer aided thermal analysis and microstructural observation showed that addition of bismuth (Bi) within the range of 0.25 and 2 wt% produced a greater effect on the Al-Si eutectic phase than on primary aluminium and Al2Cu phases. Results showed that with addition of 1 wt% Bi the eutectic silicon structure was refined from flake-like morphology into lamellar. Bi refines rather than modifies the Si structure and increases the Al-Si eutectic fraction solid and more significantly there was no fading even up to 180 min of melt holding. Transmission electron microscopy study showed that the Si twin spacing decreased from 160 to 75 nm which is likely attributed to the refining effect of Bi. It was also found that addition of 1 wt% Bi increased the tensile strength, elongation and the absorbed energy for fracture due to the refined eutectic silicon structure.

Directional solidification of rod-like eutectic is an important route to produce in situ composites. The rod-like phase spacing of composites is a crucial parameter in determining the properties of the materials. In this study, the rod-like phase spacing of melt-grown in situ eutectic composites is estimated by the method that is established based on the classical Jackson-Hunt theory and completed by considering the minimum undercooling principle in eutectic solidification at steady state. The density difference between the solid phases is also considered when calculating the diffusion field in the liquid. It is found that the rod-like phase spacing of in situ eutectic composites is generally a not unique value but displays a finite range under fixed growth conditions. Also, the range width, which decreases with increasing growth rate and vice versa, is only dependent on the intrinsic properties of an alloy at a given growth rate. By comparing with the experimental observations, the results show that the predicted spacings are in reasonable agreement with experimental data for nonfaceted-nonfaceted Succinonitrile-(D)camphor, MnSb-Sb, and Al-Al3Ni alloys and faceted-nonfaceted MnBi-Bi system when growing in a coupled manner.

Recently, the use of LED is increasing. This paper presents the new package process of thermal compression bonding using metal layered LED chip for the high power LED device. Effective thermal dissipation, which is required in the high power LED device, is achieved by eutectic/flip chip bonding method using metal bond layer on a LED chip. In this study, the process condition for the LED eutectic die bonder system is proposed by using the analysis program, and some experimental results are compared with those obtained using a DST (Die Shear Tester) to illustrate the reliability of the proposed process condition. The cause of bonding failures in the proposed process is also investigated experimentally.

Physical properties – viscosity, electric conductivity, and thermoelectric power – of liquid ionic systems NaF–LaF3 and NaF–NdF3 at eutectic concentrations have been studied., Дослiджено температурнi залежностi в’язкостi, електропровiдностi та термо-ерс бiнарних iонних рiдинних систем NaF–LaF3 та NaF–NdF3 у широкому температурному iнтервалi, що включає температури плавлення цих сплавiв евтектичного складу.

The surface of AZ31 magnesium substrate is coated by Zn-Al alloys using cast-penetrated cladding. The transverse section of alloy cladding is composed of cladding zone, diffusional zone, and bonding zone. The microstructure evolution, phase constitution, and chemical composition of the transition layer are studied. The experimental results exhibit cladding zone contained dendrite matrix and interdendritic eutectic structures. The plume eutectic structure and columnar eutectic structure are formed in diffusional zone and bonding zone, respectively. Zn and Al solid solutions gradually decrease and disappear owing to the diffusion of magnesium atom and the changes of magnesium element concentration. Mg7Zn3 phases are generated rapidly due to the interdiffusion of zinc and magnesium atoms rapidly in the diffusional zone and bonding zone. As Mg-Zn eutectic phases hinder the movement of Mg and Al atoms, the Mg-Al intermetallic compounds are eliminated completely. The microstructure is transformed into Mg solid solution and Mg7Zn3 eutectic structure to combine with AZ31 base metal.

In non-equilibrium conditions, the coring phenomena may occur in the α-Mg solid solution and γ-Mg17Al12 phase forms in the microstructure of AZ magnesium alloy series. This eutectic phase may introduce detrimental effect on workability of wrought alloys. In the present work, the dissolution characteristics of γ phase have been investigated in AZ31 wrought magnesium alloy. Considering the eutectic temperature of AZ31 alloy, the homogenization treatment was executed in temperature range of 300-437 ºC (i.e., somewhat below eutectic melting temperature of γ precipitate) and 437-500 ºC (i.e., higher eutectic melting temperature of γ precipitate) for different durations. A thorough microstructural investigation and also thermodynamic calculations were executed. The results indicated that the dissolution rate of γ phase is very low even at temperatures just below the eutectic point of the alloy, whereas it dramatically increases at temperatures higher than eutectic point. Moreover, it is suggested that partial melting of γ phase due to eutectic melting reaction (α+γ→L) may lead to reduced formability.

Transient liquid phase (TLP) diffusion bonding was carried out on nanostructured metal matrix composite sheets of Al-1100 alloy with 5 wt-% alumina particles at various bonding temperatures and process durations. A thin layer of 5 μm pure copper was electrodeposited as an interlayer. Joint formation was first attributed to the solid state diffusion of copper into the aluminium metal matrix followed by eutectic formation; then, base metal dissolution and isothermal solidification was completed at the joint interface. Joint area was characterised using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Diffraction patterns showed the formation of intermetallic phases like CuAl2. The concentration of Al2O3 particles increases across the interface as the bonding temperature increases. As a result, the highest bond strength of 123 MPa was achieved after a bonding duration of 30 min at 590°C.

The microstructural evolution during directional solidification of the Ni–25%Al (mole fraction) alloy was investigated in the range of growth velocity from 10 to 100 μm/s under a given thermal gradient of 10 K/mm. The solidification microstructures reveal a transition from γ‘–β equilibrium eutectic to γ– β metastable eutectic plus β dendrites. A mixed microstructure of γ‘– β and γ– β eutectics produced at a growth velocity of 25 μm/s illustrates that the transition occurs during the competitive growth between γ and γ' phases. The growth temperature for each phase was considered to understand the microstructure selection during solidification. The experimental results show that a phase or a microstructure solidifying with the highest temperature under a given growth condition is preferentially selected upon solidification. In addition, both stable eutectic and metastable eutectic are shown to coexist and simultaneously grow in the velocity range between 25 and 60 μm/s due to their similar growth temperatures.

In this study, we reported the fabrication of a capacitive MEMS microphone packaged with an analog amplifying chip. The MEMS device and the amplifying chip were made using a micromachining technique and an IC Multi-Project Chip (MPC) service, respectively. The MEMS device consisted of a low stressed SiNx membrane that is sensitive to sound and the rigid Si back plate. The membrane and the back-plate parts fabricated separately on two wafers were bonded through a eutectic bonding process. Finally, the MEMS device and the amplifying chip were packaged on a single PCB for measuring. The evaluation results of the packaged microphone devices showed similar characteristics compared to FEM simulation results. The sensitivity of the microphone was about −37.4 dB in audio frequency bandwidth.

The conversion to RoHS-compliant lead-free assembly has been a considerable challenge to the electronics industry. Among several alternative solder alloys, Bi–Ag alloys have been highlighted as a potential candidate to replace high Pb solder alloys for applications in oil and gas, automotive and avionics industries. The typical melting temperatures of Bi–Ag near-eutectic alloys are considered acceptable and excellent mechanical properties may be achieved with appropriate microstructures. Such promising alloys for high temperature soldering remain barely understood especially regarding non-equilibrium solidification features. In this study, a directional solidification experiment was carried out with the Bi–2.5 wt%Ag eutectic so that a large range of cooling rates ( T ) could be obtained under unsteady-state conditions. The experimental investigation include: thermal solidification parameters (growth rate, v and cooling rate, T ), microstructure parameters (eutectic/dendritic spacing, interphase spacings) and phases morphologies analyzed by optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and hardness. Experimental interrelations between hardness and microstructure (scale and morphology) of the eutectic Bi–Ag are reported. Solidification parameters are also associated with each configuration observed along the casting, i.e., coexistence of dendrites and eutectic cells for regions very close to the cooled casting surface, eutectic cells prevailing and eutectic cells together with β-Bi primary phase. The cell spacing, λc, is correlated with hardness by Hall–Petch type equations.

The paper provides a new insight into the modification of eutectic Si in Al-Si based alloys. To date, impurity-induced twinning mechanism and twin plane re-entrant edge mechanism are the well-accepted theories. However, neither IIT nor TPRE can be used to interpret all modification observations. Therefore, a re-consideration of modification mechanisms is still required. In this contribution, recent advances on the understanding the modification of eutectic Si are reviewed. Two different cases are highlighted. In the case of Sr, Na and Eu addition, eutectic Si was modified from a faceted to a fibrous morphology, which involves the formation of multiple Si twinning. In the case of Yb and Ca addition, eutectic Si was refined to a smaller size, but still maintained a plate-like morphology. The possible modification mechanism was thus discussed in terms of (i) adsorption of atoms at twin re-entrant edge, and (ii) segregation across {111}Sigrowth planes. Furthermore, solute entrainment of modifying elements (M) was introduced to interpret the formation of Al2Si2M phase or M-rich clusters within Si crystals.