Transient Liquid Phase Research Articles

All‐Mg3Sb2‐Based Module for Thermoelectric Power Generation

Abstractn‐Type Mg3(Sb, Bi)2 shows great prospects in mid‐temperature power generation due to its extraordinary thermoelectric (TE) performance, low‐cost, and environment‐friendly attributes. However, its practical application is hindered by the slow progress of its p‐type counterpart. Herein, a high ZT of ≈0.9 at 773 K is achieved for p‐type Na0.01Mg1.7Zn1Yb0.25Sb2 through manipulation of the electronic transport properties. Then thermal expansion matched barrier material Fe75Sb25 is subtly obtained for Na0.01Mg1.7Zn1Yb0.25Sb2. The contact resistivity no longer increases significantly after aging for 72 hours at 673 K and tends to stabilize, remaining below ≈17 µΩ cm2 after 168 hours. Paired with the high‐performance n‐type Mg3(Sb, Bi)2, the transient liquid phase bonding technique is adopted to connect the hot side of the all‐Mg3Sb2‐based legs to electrode at low temperature, which enables service at high temperature. This all‐Mg3Sb2‐based module displays a high efficiency of ≈8.3% at a temperature difference of ≈430 K and shows good thermal stability when the hot side temperature is maintained at 673 K. This work merits the great potential of the all‐Mg3Sb2‐based device for heat recovery.

Microstructural stability enhancement and mechanical reinforcement of TLP-bonded Cu/Sn-3.5Ag/Cu microbumps under multiple reflow cycles through Zn Alloying and Ni substrate integration

The transient liquid phase (TLP) bonding process is effective for constructing stacked structures in advanced packaging, as it allows for multiple reflow cycles without remelting. However, the various reflows can cause phase transformations, leading to internal stress-induced voids. Thus, the stability of IMC phases is particularly challenged in 3D stacking structures. Common configurations include Cu/Sn/Cu and Cu/Ni/Sn/Cu. Although Ni improves the stability of the Cu6Sn5 phase, phase transformation to Cu3Sn can still occur, compromising reliability. This study investigates microstructure stability by doping Zn into the Cu/Sn-3.5Ag/Ni system across five reflow cycles. Results demonstrate that Cu-15Zn/Sn-3.5Ag/Ni microbumps reduce void formation and ensuring the phase stability of the (Cu,Ni)6(Sn,Zn)5 to maintain the microstructure stability. The Zn addition inhibits the Cu3Sn layer, while optimizing grain size and orientation of (Cu,Ni)6(Sn,Zn)5. (Cu,Ni)6(Sn,Zn)5 also exhibits increased hardness and reduced modulus (Er). These findings provide critical insights for designing sub-10-μm scale TLP-bonded microbumps in advanced packaging.

Effects of Sn addition in W-doped Ag paste against electrochemical corrosion and sulfurization

Purpose This study aims to address these challenges by enhancing the resistance of Ag-based pastes to corrosion and sulfurization, thereby improving their performance and weatherability in high-power and high-frequency electronic applications. Design/methodology/approach This study investigates the influence of Sn doping in W-doped Ag paste to enhance resistance against electrochemical corrosion and sulfurization. A systematic examination was conducted using transient liquid phase sintering and solid–liquid inter-diffusion techniques to understand the microstructural and electrochemical properties. Findings This study found that Sn addition in W-doped Ag paste significantly improves its resistance to electrochemical corrosion and sulfurization. The sintering process at 600°C led to the formation of an Ag2WO4 phase at the grain boundaries, which, along with the presence of Sn, effectively inhibited the growth of Ag2WO4 grains. The 0.5% Sn-doped samples exhibited optimal anti-corrosion properties, demonstrating a longer grain boundary length and a passivation effect that significantly reduced the corrosion rate. No Ag2S phase was detected in the weatherability tests, confirming the enhanced durability of the doped samples. Originality/value The findings of this study highlight the potential of Sn-doped Ag-W composites as a promising material for electronic components, particularly in environments prone to sulfurization and corrosion. By improving the anti-corrosion properties and reducing the grain size, this study offers a new approach to extending the lifespan and reliability of electronic devices, making a significant contribution to the development of advanced materials for high-power and high-frequency applications.

Realizing Ultrahigh Conversion Efficiency of ≈9.0% in YbCd2Sb2/Mg3Sb2 Zintl Module for Thermoelectric Power Generation.

Recently, YbCd2Sb2-based Zintl compounds have been widely investigated owing to their extraordinary thermoelectric (TE) performance. However, its p orbitals of anions that determined the valence band structure are split due to crystal field splitting that provides a good platform for band manipulation by doping/alloying and, more importantly, the YbCd2Sb2-based device has yet to be reported. In this work, single-phase YbCd1.5Zn0.5Sb2 is successfully obtained through precise chemical composition control. Then, YbMg2Sb2-alloying increases the cationic vacancy defect formation energy and further optimizes carrier concentration. Moreover, the band structure of YbCd1.5Zn0.5Sb2 is subtly manipulated, and the underlying mechanism is experimentally explored. Combined with the reduced lattice thermal conductivity, a high peak ZT value of ∼1.43 at 700K is obtained for YbCd1.425Zn0.475Mg0.1Sb2. Subsequently, choosing Fe90Sb10 as the diffusion barrier layer and adopting the transient liquid phase bonding technique, for the first time, it is demonstrated that YbCd2Sb2/Mg3(Sb, Bi)2 TE module with an ultrahigh conversion efficiency of ≈9.0% at a heat difference of 430K. More importantly, this module displays good thermal stability. This work paves the way for YbCd2Sb2 materials and devices in mid-temperature heat recovery.

Transient Liquid Phase Bonding of ZGH451 Superalloy Fabricated by Directed Energy Deposition

ZGH451, a directionally solidified Ni‐based superalloy designed for additive manufacturing, has garnered significant attention in the realm of next‐generation turbine blades. Welding the ZGH451 superalloy is crucial for promoting its practical application. In this study, transient liquid phase (TLP) bonding is applied to weld ZGH451 superalloy produced through directed energy deposition. A Ni‐based interlayer alloy powder is developed and prepared via thermodynamic calculation, with the interlayer subsequently characterized using differential thermal analysis. TLP bonding is conducted at 1200 °C for 4 h. The influence of the preset gap on the joint microstructure and mechanical properties is examined. The microstructure of the TLP bonding joints comprises athermally solidified zones (ASZ), isothermally solidified zones, and diffusion‐affected zones. The ASZ width significantly increases with the growing preset gap. A preset gap not exceeding 100 μm enables complete isothermal solidification of the joints. Particularly, joints with a preset gap ranging from 0 to 30 μm demonstrate optimal reliability, exhibiting a tensile strength of up to 1375 MPa at room temperature, which is 12% higher than the room temperature strength of the base metal (BM), and a tensile strength of 983 MPa at 760 °C, surpassing 86% of the BM's strength at the same temperature.

Numerical characterizations of the thermomechanical response of power modules with ceramic substrates and lead-free bonds

PurposeThe present paper aims to study the influence of the substrate system on the thermomechanical response of various lead-free die attach materials used in power electronics using nonlinear finite element simulations.Design/methodology/approachParticularly, three ceramic substrate systems, including direct copper bonded (DCB) and aluminum nitride (AlN) – as well as silicon nitride (Si3N4) –based insulated metal substrate (IMS) configurations are examined in this study. Additionally, three die attach systems, namely, silver-tin transient liquid phase (TLP), sintered silver (Ag) and sintered copper (Cu) are included in the analysis. ANSYS software is employed to build the finite element models of the power modules and to conduct the nonlinear thermomechanical investigations.FindingsThe simulation results revealed that the IMS, Si3N4 and DCB-based power modules end up with significantly lower interconnect inelastic strains and inelastic strain energies suggesting better fatigue life performance. Additionally, the bonding layer stresses and expected failure mechanism are not influenced by the substrate configuration rather than the bond material. For instance, the silver-tin TLP joints develop high stresses and hence brittle failures are expected. Nonetheless, the sintered Ag and sintered Cu have significantly lower stresses which could lead to fatigue-induced failures.Originality/valuePower electronics use various ceramic-based substrate systems because of their improved thermal conductivity, electrical insulation and heat resistance properties. The proper selection of the substrate structure could highly enhance the thermal fatigue of the power modules. Markedly, the findings of this research are useful for designing highly reliable and effective power modules continuously subjected to thermomechanical loadings.

Joining of SiC ceramics by iridium: The interfacial phenomena and joint strength

A methodology for joining SiC ceramic parts using iridium foil was devised. The connecting layer was formed via a solid-state reaction at 1350 °C or via a transient liquid phase (TLP) at temperatures exceeding 1417 °C. The microstructure of the connecting layer formed via solid-state reaction exhibits temporal changes. The overall thickness of the layer remains approximately constant over time; however, the thickness of the carbon-free central part, composed of Ir and iridium silicides, decreases with time. The thicknesses of the porous carbon-containing sublayers located on either side of the central region demonstrate an increase. The greatest average flexural strength value was found to be 110 ± 6 MPa. The flexural strength values decrease with an increase in the holding time. This behavior can be attributed to the growth of a porous carbon-containing layer. The connecting layer, obtained via a transient liquid phase, is composed of IrSi and C. The layers on either side of the central dense IrSi part contain a number of pores and carbon inclusions. The SiC/SiC joints formed at 1425 °C and 1500 °C exhibit bending strengths of 66 ± 4 and 29 ± 4 MPa, respectively. These findings illustrate the potential of iridium to join monolithic SiC ceramic parts at relatively low temperatures.

Microstructural characteristics and mechanical response of transient liquid-phase diffusion bonding AlCoCrFeNi2.1 high entropy alloy utilizing BNi-5 interlayer

This study focuses on the microstructural characteristics and mechanical response of the transient liquid phase (TLP) diffusion-bonded joints of AlCoCrFeNi2.1 high entropy alloy. Bonging parameters were chosen and optimized for the AlCoCrFeNi2.1 alloy and the TLP joining mechanism. The relatively complete isothermal solidification zone (ISZ) ensured a reliable connection of the base metal. As the bonding temperature increased from 1060 °C to 1160 °C, the athermal solidification zone (ASZ) disappeared. The homogenization degree of elements in the ISZ continuously increased, the matrix γ phase became fully ordered, and the B2 phase was precipitated, achieving high entropy state in the ISZ of the joint. Additionally, semi-coherent relationships of [0, 1, 1] L12, [0, 1, 1] B2 and (1, 1̅,1) L12, (2̅, 3, 1̅) B2 were detected between the B2 precipitate phase and the L12 matrix. The phase distribution in the ISZ significantly influenced the mechanical properties of the joint. The complete ordering of the matrix phase at 1160 °C eliminated deformation incoordination between the ISZ and the diffusion-affected zone (DAZ). The B2 phase transitioned from precipitating at the grain boundary at lower temperatures to precipitating uniformly in the ISZ, eliminating the weakening effect of the grain boundary and resulting in tensile strength and elongation comparable to the base material. The fracture morphology indicated a mixed fracture mode.

Recent Developments in Low Temperature Wafer Level Metal Bonding for Heterogenous Integration

Abstract An overview of various low-temperature (<200°C) wafer bonding processes using metal interlayers is presented. Such processes are very attractive for novel applications in 3D heterogenous packaging as the allow for simultaneous formation of electrical interconnects, as well as hermetic encapsulation of various sensors and microelectromechanical systems-based devices. Metal wafer bonding is a generic category of processes consisting of various sub-categories, each one defined by the different principles governing the process. One can differentiate between eutectic wafer bonding (a eutectic alloy is formed as bonding layer during the process by liquid-solid interdiffusion), intermetallic wafer bonding (an intermetallic alloy is formed as bonding layer during the process by solid-liquid interdiffusion, a process known also as solid liquid intermetallic diffusion transient liquid phase, and metal thermo-compression wafer bonding. Different critical/gating parameters were investigated and their impact for generally reducing processing temperatures for the different metal bonding systems was studied.

A Novel Two-Step, Transient Liquid Phase Sintering Process for Densification of Binder-Jet 3D Printed Superalloys

A Novel Two-Step, Transient Liquid Phase Sintering Process for Densification of Binder-Jet 3D Printed Superalloys

Tin Multilayer‐Aided SAC305‐Based Lead‐Free Solder Joint Interface with Cu: An Investigation of the Stress Distribution by Finite Element Analysis and Nanoindentation Studies

Two different types of lead‐free solder joints Cu/(Sn3.0Ag0.5Cu)/Cu and Cu/Sn/(Sn3.0Ag0.5Cu)/Sn/Cu have been investigated. Joints are produced following the transient liquid phase like soldering process. The microstructure of different intermetallic compounds (IMCs) present at the joint interfaces, as well as their indentation hardness and elastic modulus, have been investigated and analyzed using scanning electron microscopy (SEM), X‐ray diffraction (XRD) spectroscopy, and nanoindentation. The exact position of different microcracks inside the interfaces has been identified by analyzing the elastic–plastic properties and interfacial toughness of these solder joints. The modulus and hardness of the Sn multilayer‐assisted solder joint interface are found to be 60.08%, and 90.18% higher than those of its non‐layered counterpart, respectively. The finite element analysis (FEA) has been done to estimate and compute stress distributions over the interfacial region. The dislocation mechanics involved in strengthening the joint strength are related to the nature of stress flow; as observed in FEA. It is reconfirmed that the high susceptibility to brittle failure of the non‐layered Cu‐SAC305 solder joints could be avoided by using a Sn interlayer in between the Cu substrates and the SAC305 solder paste.

Microstructure and tensile properties of transient liquid phase (TLP) sintering repaired Ti–6Al–4V alloys with large area hole defect

Repairing defects in titanium alloy components is economically justified due to their high cost. In this work, Ti–6Al–4V samples with large area hole defects are repaired by transient liquid-phase sintering. The microstructure and tensile properties after repair have been investigated. The factors of different base powder morphology and the ratio of braze metal are also studied. The results show that by using spherical Ti64 alloy powder with 40 wt% TiZrCuNi braze alloy powder, an overall repair effect with high-density repair zone and good interface combination can be obtained at 960 °C for 3 h. The tensile strength of the as-repaired exceeds that of the matrix, but the elongation is lower than that of the matrix. Finally, the repair experiment conducted at various angles demonstrates this technique's strong practical feasibility.

Transient Liquid Phase Bonding by Two-Step Heating Technique of IN939

Transient Liquid Phase Bonding by Two-Step Heating Technique of IN939

Transient liquid phase bonding of Hastelloy X to Ni3Al intermetallic compound: Microstructure and phase transformation study

The microstructure of dissimilar transient-liquid-phase (TLP) bonding of Hastelloy X nickel base super alloy to Ni3Al intermetallic by AWS BNi2 filler metal at different temperatures (1000–1150 °C) and time ranges (60–180 min) was investigated. A novel study was done to correlate the phase transformation during bonding with microstructure and phase transformation using field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HR-TEM), and high temperature X-ray diffraction (HTXRD). Efforts were performed to correlate the phase transformation stages during isothermal solidification (IS), formation of Cr-Mo precipitates in diffusion affected zone (DAZ) and dissolution of nickel silicides (eutectic morphology) in athermal solidification zone (ASZ) with their respective reaction temperatures. The high tendency of Hastelloy X to react intensely with filler metal generated Mo-Cr rich phase in DAZ. The ISZ was developed across the joint area after holding at 1100 °C for 180 min. High temperature XRD results on half joint of HX revealed new phases generated at above 1050 °C including BNi2,BNi3, and Ni2Si (Ni-Si eutectic phase) confirmed by FESEM. On the other half joint (Ni3Al), no BNi phases were generated nor nickel silicides by increasing temperature as high as 1150 °C.

The Effect of Bonding Time and Temperature on Microstructure and Mechanical Properties of SS316L/WC-Co Dissimilar Joint Produced by Transient Liquid Phase Bonding

The Effect of Bonding Time and Temperature on Microstructure and Mechanical Properties of SS316L/WC-Co Dissimilar Joint Produced by Transient Liquid Phase Bonding

Study on rapid growth and improved performance of superconducting YBa2Cu3O7-δ coated conductors assisted by transient liquid phase

This study employs a fluorine-free metal organic deposition method (FF-MOD), with transient liquid phase assistance, to expedite the growth (TLAG) of superconducting YBa2Cu3O7-δ (YBCO) thin films on LaMnO3 metal substrates. The research evaluates the phase formation and performance of YBCO films with varying proportions of preformed BaZrO3 (BZO) nanocrystals. The experimental results indicate that the optimal proportion for incorporating BZO nanocrystals is 5 %, leading to the YBCO film displaying critical current density at 77 K under zero-field conditions. This achievement marks a significant advancement in the rapid growth of YBCO films on metal substrates with enhanced current-carrying capacity. Additionally, the research assesses the changes in overall uniformity and microstrain of YBCO films after the addition of BZO nanocrystals, shedding light on the key factors contributing to performance enhancement and offering insights for future improvements. This investigation offers valuable insights for attaining high-speed, high-performance growth of superconducting YBCO coating conductors.

Transient liquid phase sintering in spark plasma sintered tungsten heavy alloys with Nb and Mo additives

In the present investigation spark plasma sintered tungsten heavy alloys of composition 90W-7Ni-3Fe, 84W-7Ni-3Fe-6Mo, and 84W-7Ni-3Fe-6Nb were analyzed to determine the effect of Mo and Nb addition on microstructure and phase formation. The alloys were sintered at temperatures ranging from 1150 °C to 1275 °C and at a fixed sintering pressure of 30 MPa. Nb added alloy exhibited a maximum relative density of 99% at sintering temperature of 1200 °C. Whereas the base alloy and Mo added alloy, exhibited a maximum relative density of 97.9% and 95.9% at 1150 °C respectively. Transient liquid phase sintering was found to play a crucial role in the base alloy and Mo added alloy whereas the Nb added alloy was found to undergo persistent liquid phase sintering. Microstructure characterisation by SEM revealed formation of finer tungsten grains with average grain size ranging from 1 μm to 4.3 μm. Mo addition restricted the tungsten grain growth while Nb addition promoted the tungsten grain growth compared to the base alloy. Phase analysis by XRD revealed the formation of Ni4W intermetallic (at lower temperatures) for the base alloy, NbO2 and NbW intermetallics for Nb added alloy and MoNi rich phase for Mo added alloys. Hardness measured by Vickers hardness method revealed a declining trend in hardness with increase in sintering temperature, owing to tungsten grain growth in all the alloys and along with Kirkendall pore formation and growth for the base alloy and Mo added alloy. Nb addition resulted in maximum hardness of 678 HV1 which is highest ever reported for SPSd WHA with 90 wt% concentration of W.

Enhancing mechanical properties of lanthanide zirconates through the cold sintering assisted sintering process

This study evaluates the impact of incorporating varying contents (10–40 wt%) and molar concentrations (0.001–1 M) of citric acid solutions, as transient liquid phases in the Cold Sintering Assisted Sintering (CSAS) process of dysprosium zirconate (Dy2Zr2O7). CSAS processed samples achieved relative densities up to 98% of the theoretical maximum and significantly increased Vickers microhardness by over 2.5 times, compared to the traditional ‘press and fired’ sintering method. The Dy2Zr2O7 crystal structure remained consistent with the fluorite-type, with no secondary phases detected. Our findings underscore the benefits of using CSAS to enhance the mechanical strength of Dy2Zr2O7, while reducing the lengthy processing times at very high temperatures typically required for sintering refractory materials such as lanthanide zirconates.

Fine-tuning the microstructure for improved performance in cold-sintered Li1.3Al0.3Ti1.7(PO4)3 composite solid electrolytes

Solid-state electrolytes (SSE) are one of the fundamental components of the upcoming generation of batteries since they increase the operational safety and efficiency. In this work, composite solid electrolytes (CSE) based on Li1.3Al0.3Ti1.7(PO4)3 and a (PEO2-LiTFSI) polymer matrix are obtained via the pioneering Cold Sintering Process (CSP), with a drastic reduction of the conventional sintering temperature. The CSP is performed at only 150 °C and 700 MPa, for 90 min of sintering time, by using a 3m acetic acid solution as the transient liquid phase (TLP). Here, the effect of the LATP particle size (d50) is studied to tailor the final microstructure, which enables the fine-tuning of the ultimate electrical properties of the electrolyte. An optimum d50 of 0.415 μm produces CSEs with 91 % of relative density, an ionic conductivity of 0.169 mS/cm, activation energy of 0.293 eV and electrical stability under 0.1 mA/cm2, thus leading to competitive properties.

Effect of Al particles addition on microstructure and shear properties of Cu/Sn-1Zn/Cu composite solder joints by transient liquid phase bonding

Sn-Zn solders have great potential in the field of 3D packaging applications due to the low melting point and low cost. However, there are still some problems prevented the development of Sn–Zn solder. Adding reinforcing particles helps to improve the reliability of solder joints. Cu/Sn-1Zn-xAl/Cu (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) solder joints were prepared by transient liquid phase bonding (TLPB) method. The effects of Al particle content on the interfacial microstructure and shear properties of solder joints were studied. The results show that the phases of the interface layer are Cu3(Sn, Zn) and Cu6(Sn, Zn)5. With the increase of Al particle content, the thickness of intermetallic compounds (IMC) layer decreases first and then increases. When the Al content is 0.6 wt%, the minimum value is 4.37μm. The porosity of the solder joints also decreases first and then increases with increasing of the Al particles content. As the increase of Al particles content, the shear strength of solder joints increases first and then decreases. The shear strength of Cu/Sn-1Zn/Cu solder joint is 12.51 MPa. With adding 0.6 wt% Al particles, the shear strength of the Cu/Sn-1Zn-0.6Al/Cu solder joint reached its maximum value of 19.29 MPa, which is 54.20 % higher than that of Cu/Sn-1Zn/Cu solder joint. The fracture mode of Cu/Sn-1Zn-0.6Al/Cu solder joint is ductile-brittle mixed fracture, and the fracture location is at the junction of in-situ reaction zone and interface reaction zone.