Transient Liquid Phase Research Articles

Cu-Cu joint with Sn-58Bi/Porous Cu/Sn-58Bi transient liquid phase bonding under formic acid atmosphere

PurposeThis paper aims to examine the effects of bonding temperature, bonding time, bonding pressure and the presence of a Pt catalyst on the bonding strength of Cu/SB/P-Cu/SB/Cu joints by transient liquid phase bonding (TLPB).Design/methodology/approachTLPB is promising to assemble die-attaching packaging for power devices. In this study, porous Cu (P-Cu) foil with a distinctive porous structure and Sn-58Bi solder (SB) serve as the bonding materials for TLPB under a formic acid atmosphere (FA). The high surface area of P-Cu enables efficient diffusion of the liquid phase of SB, stimulating the wetting, spreading and formation of intermetallic compounds (IMCs).FindingsThe higher bonding temperature decreased strength due to the coarsening of IMCs. The longer bonding time reduced the bonding strength owing to the coarsened Bi and thickened IMC. Applying optimal bonding pressure improved bonding strength, whereas excessive pressure caused damage. The presence of a Pt catalyst enhanced bonding efficiency and strength by facilitating reduction–oxidation reactions and oxide film removal.Originality/valueOverall, this study demonstrates the feasibility of low-temperature TLPB for Cu/SB/P-Cu/SB/Cu joints and provides insights into optimizing bonding strength for the interconnecting materials in the applications of power devices.

A Review of Recent Research Trends of Forming of Metallic Bondlines Using Core-Shell Particles and Bonding Properties According to Particle Type

With the increasing numbers of electric vehicles and the prevalence of high heat generating devices, recent studies have attempted to address the limitations of conventional solder materials, including their low durability at temperatures exceeding 200 ℃, insufficient mechanical properties in a joint, and low thermal conductivity. Transient liquid-phase (TLP) partial bonding using solders or Sn, and sinter bonding using Ag particles, are alternative bonding methods which involve a modification or change of the material. Advanced alternatives can significantly reduce bonding time or material cost. Various additional studies have investigated various core-cell particles that can be used to form an all-metallic bondline. This review summarizes reports of bonding studies using different core-cell particles. The particles were not only applied as a form of paste but also preform. In the TLP bonding using X(Cu, Ag, Ni)@Sn particles, the degree of voids generated in the formed bondline was dependent on the type of intermetallic compound formed. The preforms consisting of X@Sn particles provided relatively uniform microstructure and void distribution, compared to the pastes containing identical X@Sn particles, resulting in better long-term mechanical reliability. The addition of Zn@Sn particles contributed to the more practical control of microstructure and mechanical properties in the joint formed by pure Sn and Sn-58Bi solder alloys. Cu@Ag particles can be considered a promising low-cost material for compression-assisted sinter bonding, replacing pure Ag particles. The application of core-cell particles is expected to improve the processes used for forming metallic bondlines.

Effect of Pd addition in BNi-2 interlayer on microstructure and properties in the TLP joints of FeCoNiTiAl and FGH98 alloys

L12-strengthed High-entropy alloys (HEAs) have attracted much attention in the field of manufacturing components that need to serve in high-temperature environments like aviation engine due to their high strength, toughness, and excellent high-temperature mechanical performance. Moreover, owing to great comprehensive mechanical properties, powder metallurgy (PM) superalloys have been widely applied for fabricating key parts of aircraft engine such as turbine disks. Hence, joining the two kinds of alloys is significant and potential in the engine manufacturing field. The key points to achieve joint with high strength and ductility (even at high temperature) were composition design of interlayer and the optimization of bonding parameters. In this study, Transient liquid phase (TLP) bonding was applied for joining HEA of FeCoNiTiAl and FGH98 superalloy using BNi-2 interlayer with addition of Pd. The experimental results demonstrate there were multiple second phases including γ’, borides (M3B2 and TiB2), etc., precipitated in the TLP joint. Furthermore, with the bonding time increased, accumulation of Al diffused from BMs can lead to a eutectic reaction of L → γ’ + AlPd + Cr5B3 occurred in the centerline of joint, which was harmful to the joint properties. Therefore, after bonding for 30 min at 1150 °C, owing to homogeneous joint microstructure of no defects and little eutectic compounds, the highest shear strength of 934 MPa was achieved.

The study of Ni-Sn transient liquid phase bonded joints under high temperatures

To develop new electronic packaging techniques for harsh environments, the microstructure and associated mechanical properties of NiSn transient liquid phase (TLP) bonded at high temperatures have been investigated in this work. The effect of bonding temperature (from 400 °C to 700 °C) on the microstructure and mechanical properties of joints has been studied. In addition, the growth kinetics of Ni3Sn2 and Ni3Sn intermetallic compounds (IMCs) have been studied to analyse the phase transformation mechanisms and microstructure evolution of joints bonded at 500 °C for different times. Also, the long-term (up to 100 h) high-temperature (500 °C) thermal reliability of joints has been investigated. The results showed that the average shear strength increased as the bonding temperature increased from 400 °C to 500 °C, but continuously dropped as the bonding temperature further increased from 500 °C to 700 °C. It was found that volume diffusion dominated the growth mechanisms of both Ni3Sn2 and Ni3Sn IMCs during bonding at 500 °C for different times. Furthermore, as the aging (at 500 °C) time increased from 0 h to 100 h, the average shear strength of joints continuously decreased. The joints aged for 50 h shear fractured mainly within the Ni3Sn2 IMCs, while the joints after aging for 100 h fractured mainly through the Ni3Sn IMCs.

In operando characterization of the ionic conductivity dependence on liquid transient phase and microstructure of cold-sintered Bi2O3-doped Li1.3Al0.3Ti1.7(PO4)3 solid-state electrolyte

A disruptive sintering technique, Cold Sintering Process (CSP), has been used to produce cold-sintered samples of Bi2O3-doped Li1.3Al0.3Ti1.7(PO4)3 (LATP) as solid-state electrolyte (SSE). An in operando impedance study has been performed to shed light on this sintering process. In this work, Bi2O3 and 3 m acetic acid solution sintering aids were synergistically added to LATP powders to sinter at low temperature. Effects of Transient Liquid Phase (TLP) content on the sintering behavior, phase composition, microstructure, and electrochemical properties were all investigated for a LATP doped with 2 wt% Bi2O3 (optimal content) solid-state electrolyte (SSE). The data revealed that the final electrical properties, which are the key parameter decisive for their application, are defined by the following sintering parameters: Transient Liquid Phase (TLP) content, temperature, pressure, and dwell time. Using acetic acid 3 m as TLP, LATP-based samples can be cold-sintered at optimized sintering conditions of 150 °C and 700 MPa of uniaxial pressure for 90 min. The resultant SSE shows a high ionic conductivity (4.5·10−5 S cm−1) at room temperature (RT) and relative density (∼95%), which demonstrates the effectiveness of the low-temperature sintering process by optimizing the ionic conductivity of LATP-based SSE, also reducing preparation costs and CO2 emissions.

Introducing an ionic conductive matrix to the cold-sintered Li1.3Al0.3Ti1.7(PO4)3-based composite solid electrolyte to enhance the electrical properties

In the present work, a Polymer-In-Ceramics (PIC) solid electrolyte based on Li1.3Al0.3Ti1.7(PO4)3 (LATP) and PEOn-LiTFSI (poly(ethylene oxide) - lithium bis(trifluoromethanesulfonyl)imide) is obtained via Cold Sintering Process (CSP), at a temperature of 150 °C without any post-heat treatment, this is 900 °C below the traditional sintering temperature. This novel study demonstrates the effect of the Transient Liquid Phase content (TLP) and the composition of the polymeric active filler on the final Composite Solid Electrolyte (CSE) properties, with the sintering process being monitored by in-operando Electrochemical Impedance Spectroscopy (EIS). Firstly, the 15 wt% of TLP is stated as the optimal liquid content based on the electrical answer and workability. Then, the (EO:Li+) molar ratio is studied from (1:1) to (8:1). The highest ionic conductivity of 1.04·10−4 S cm−1 and a relative density above 98% are achieved at room temperature when the TLP content is 15 wt% and the molar ratio (2:1), with the LATP content set in 90 wt%. Moreover, the activation energy (Ea) is drastically reduced, from 0.388 eV (LATP ceramic electrolyte) to 0.298 eV (PIC electrolyte), with a lithium transference number (tLi+) close to 1. Therefore, this research work proposes a potential solid electrolyte to substitute the traditional liquid electrolytes.

Effects of Transient Liquid Phase Bonding Time on Microstructure, Mechanical and Corrosion Properties During Bonding of Inconel 617/AISI 310 Stainless Steel

Effects of Transient Liquid Phase Bonding Time on Microstructure, Mechanical and Corrosion Properties During Bonding of Inconel 617/AISI 310 Stainless Steel

Transient liquid phase bonding assisted spark plasma sintering of La-Fe-Si magnetocaloric bulk materials

The poor mechanical properties of La-Fe-Si based alloys restrict the potential of these magnetocaloric materials. Hence, a novel transient liquid phase bonding (TLPB) processing technique was deployed during spark plasma sintering (SPS) of La-Fe-Si based bulk materials. A series of binder-free LaFe11.8Si1.2 bulk materials were prepared by SPS and hot-pressing sintering (HPS). Transient melting, which occurred during SPS, accelerated the decomposition of the 1:13 phase, resulting in low porosity and high strength. Compared to HPS samples, SPS samples have significantly larger maximum compressive strength (σbc)max of ∼637.9 MPa at a strain of 4.7%, good thermal conductivity of ∼7.6 W·m−1·K−1 at 300 K, and a large (−ΔSM)max value of ∼11.7 J·kg−1·K−1 at TC= 193 K under a magnetic field change of 0 − 5 T. Thus, binder-free La-Fe-Si based bulk magnetocaloric materials with an excellent property set have been successfully prepared by TLPB assisted SPS technology.

Impact of Bonding Temperature on Microstructure, Mechanical, and Fracture Behaviors of TLP Bonded Joints of Al2219 with a Cu Interlayer.

The present study aims at producing transient liquid phase (TLP) bonded Al2219 joints with pure Cu (copper) as an interlayer. The TLP bonding is carried out at the bonding temperatures in the range of 480 to 520 °C while keeping the bonding pressure (2 MPa) and time (30 min.) constant. Reaction layers are formed at the Al-Cu interface with a significant increase in diffusion depth with the increase in the bonding temperature. The microstructural investigations are carried out using scanning electron microscopy and energy-dispersive spectroscopy. X-ray diffraction study confirms the formation of CuAl2, CuAl, and Cu9Al4 intermetallic compounds across the interface of the bonded specimens. An increase in microhardness is observed across the bonding zone with the increase in the bonding temperature, and a maximum hardness value of 723 Hv is obtained on the diffusion zone of the specimen bonded at 520 °C. Furthermore, the fractography study of the bonded specimens is carried out, and a maximum shear strength of 18.75 MPa is observed on the joints produced at 520 °C.

Study on the interfacial evolution and mechanical properties of Cu/SAC105/Cu solder joint modified by Si3N4 nanowires

In the present study, Si3N4 nanowires (NWs) with a mass fraction of 0.6 wt% were incorporated into Sn1.0Ag0.5Cu (SAC105) solder. Cu/SAC105/Cu and Cu/SAC105-Si3N4/Cu 3D structure joints were constructed by transient liquid-phase (TLP) bonding. To investigate the influence mechanism of Si3N4 NWs, the interfacial IMC evolution and mechanical properties of two solder joints were analyzed. It was found that the interfacial Cu3Sn IMC layer thickness of the joints containing Si3N4 NWs was thinner than that of the undoped ones at any given time. The growth of interfacial Cu6Sn5 IMC was inhibited, resulting in the retarded formation of interfacial IMC bridging and full-IMC joints. In addition, combined with the fracture morphology analysis, the brittle fracture behavior of the solder joints was suppressed, and the shear strength of the joints showed a significant improvement following the introduction of Si3N4 NWs. Moreover, Si3N4 NWs were found exposed on the fracture surface of Cu3Sn IMC layer, demonstrating that the doping of Si3N4 NWs shaped a joint similar to that of reinforced concrete structure, which facilitates the limitation of dislocations and crack expansion.

Effect of Holding Time on Microstructure and Mechanical Properties of Dissimilar γ'‐Strengthened Superalloys TLP Joint

To achieve efficient connectivity of dissimilar γ'‐strengthened superalloy, transient liquid‐phase (TLP) diffusion bonding of 718Plus and Ni3Al‐based superalloys is carried out using BNi‐2 interlayer at a constant temperature of 1100 °C with holding times of 3, 15, 30, and 60 min. It is shown in the results that when the holding time is insufficient, isothermal solidification transforms into athermal solidification. Due to the enrichment of B and Cr elements in liquid phase, ternary eutectic consisting of γ, Ni3B, and CrB is formed at the joint center. Ternary eutectic with higher hardness (≈600 Hv) is poorly bonded to the matrix, which can easily become crack initiation location and significantly deteriorated the tensile properties. In addition, microhardness of the joint becomes more uniform and tensile strength gradually increases due to the reduction of eutectic with holding time increasing. Isothermal solidification completes and a joint without eutectic structure is formed at 1100 °C for 60 min. Diffusion of Al atoms leads to the formation of γ' with gradient size and tensile strength is comparable to that of base metal which is about 690.93 MPa.

Effect of Brazing Temperature on Microstructure, Tensile Strength, and Oxide Film-Breaking Synergy of 5A06 Aluminum Alloy Welded by TG-TLP

5A06 aluminum alloy bar was brazed by temperature gradient transient liquid phase diffusion welding (TG-TLP). The effects of brazing temperature on the microstructure and the tensile strength of the brazing joints were investigated. Three typical brazing filler alloys (1# Al-20Cu-6Si-2Ni, 2# Al-10Cu-10Si-3Mg-1Ga, and 3# Al-6Cu-10Si-2Mg-10Zn) were prepared by smelting, and TG-TLP diffusion bonding was carried out at different brazing temperatures (550 °C~590 °C). The results show that with the increase in brazing temperature, the oxide films at the brazing junction are easier to be broken and dispersed, but the oxidation extent will also increase. The oxidation products enriched were mainly Al2O3 and SiO2 at the brazing junction. There are different optimal brazing temperatures corresponding to the different filler alloys. For 1#, the optimal temperature is 570 °C; for 2# is 580 °C; for 3# is 580 °C. For 1# brazing joints, the maximum tensile strength was 113 MPa, and for 2# was 122.4 MPa. Under the experimental conditions of this study, the maximum tensile strength of the TG-TLP joint is 147.4 MPa of 3# brazing sample (at 580 °C), which has increased by 30% and 20% compared to 1# and 2# respectively. The nickel-rich phase at the interface (of 1# brazing filler) could form a brittle fracture, which was unfavorable for interface bonding. For TG-TLP brazing of 5A06, the filler alloy with high Al:Cu ratio (12:1 wt.%) needs a sufficient temperature gradient to exert the film-breaking effect, while the filler alloy with low Al:Cu ratio (3.6:1 wt.%) needs to accurately control its brazing temperature to avoid excessive oxidation. There are many research gaps in the influence of brazing material composition and brazing temperature on the microstructure and mechanical properties of 5A06 aluminum alloy TG-TLP joints. The research results can provide a theoretical basis for formulating the TG-TLP brazing specification of 5A06 aluminum alloy.

Retaining multi-oriented and fine grain structure with Ni doping in Cu/Sn-3.0Ag-0.5Cu/Cu transient liquid phase bonding under isothermal aging treatment

Transient liquid phase bonding has been proven to offer exceptional joining strength and dependable high temperature service in chip stacking applications. Nevertheless, conventional Cu/Sn/Cu transient liquid phase bumps had shortcomings, such as smooth phase boundaries and coarsening grains. In this study, the variation of microstructure in Cu/Sn-3.0Ag-0.5Cu/Cu, Cu/Sn-3.0Ag-0.5Cu/Ni, and Ni/Sn-3.0Ag-0.5Cu/Cu transient liquid phase bonds with the sizes less than 10 μm before and after long term aging were investigated. Due to the dissolution of Ni atoms from the substrates at the cold or hot end, the structure exhibited randomly-oriented and small-sized grains. After 1000 h aging treatment, the Ni-containing specimen still retained the abundant grain structure and appeared network-like morphology of Cu3Sn near phase boundaries. Additionally, the shear testing was applied in the aged samples, Ni-doped joints demonstrated better mechanical properties than Ni-free joining. The enhancement of shear strength was attributed to Ni addition, retaining the advantageous grain structure. This present work showed that doping Ni to micro-bumps could halt the deterioration of grain structure over extended usage of electronic devices in 3D-IC technology.

Microstructure and Shear properties of Sn–xZn Transient Liquid Phase Bonding in 3D-Chip Stacking Packaging

Microstructure and Shear properties of Sn–xZn Transient Liquid Phase Bonding in 3D-Chip Stacking Packaging

Research on microstructure and shear strength of Al alloy jointed by sputtered Cu thin film deposited through HiPIMS and DCMS techniques

Transient liquid phase bonding (TLP bonding) in jointing technology is a promising method for achieving precision joining of aluminum alloys and creating low-cost products for use in the electric vehicles (EVs) industry, which can contribute to a low-carbon economy. This research is primarily focused on the jointing technology of aluminum alloys and is divided into two parts. The first part involves vacuum soldering between A6063 aluminum alloy with copper layers of 1, 3 and 5 μm thickness, and tin solder under thermal treatment. The second part is Cu-Al eutectic bonding. In this study, we used Ar ions to bombard the surface of A6063 aluminum alloy to remove the oxide layer and deposited a copper layer using direct-current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS). We then analyzed the joint interface of the samples using Scanning Electron Microscope (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Scanning Acoustic Tomography (SAT) to calculate the joint ratio of the entire joint surface. Finally, we measured the shear strength to evaluate the bonding effect. The results indicate that the eutectic bonding method exhibits better bonding performance for aluminum alloys compared to the soldering method. Furthermore, the shear strength increased with increasing thickness of the sputtered copper layer. When comparing two sputtering technologies, the copper films sputtered by HiPIMS system exhibit better quality those produced by the DCMS system. As a result, aluminum alloy bonding completed with HiPIMS has higher bonding strength, demonstrating that HiPIMS is a powerful coating tool.

High temperature shear and thermal aging behavior of dissimilar transient liquid phase bonded Hastelloy X to Ni3Al intermetallic compound

Nickel super alloys and intermetallic compounds (IMCs) are candidate as strategic materials for turbine industry, because of its excellent high temperature properties. In this study, mechanical properties and thermal aging behavior (post thermal exposure) of the transient liquid phase (TLP) bonds between Hastelloy X to Ni3Al IMC at temperature range of 800–900 °C were investigated. The microstructure and fracture surfaces of the joints were examined by optical and scanning electron microscopes as well as XRD analysis. The optimum joint bonding strength was achieved for the sample treated at 1100 °C–180 min equaling to 355 ± 4.5 MPa. XRD patterns of semi-cleavage fracture surfaces revealed nickel solid solution matrix containing BNi3 and Ni3Si compounds generated at ASZ/ISA interface. The ultimate tensile strength reaches 36.5 ± 1 and 20.5 ± 1 MPa at temperatures of 800 °C and 900 °C, respectively. Fracture occurred in the IMC substrates for both temperatures were due to shrinkage porosity during solidification of IMC and mismatch of crystal lattice constants with the matrix. The thermal aging process at 900 °C for 50–500 h had a minor effect on the joint microstructure but generated TCP phases in the Hastelloy X.

Improving creep property and deformation mechanism of transient liquid phase bonded polycrystalline Ni3Al-based superalloy with post bond heat treatment

A polycrystalline Ni3Al-based superalloy was joined through transient liquid phase (TLP) bonding technique. A post bond heat treatment (PBHT) was successively conducted. Creep tests of the TLP and TLP + PBHT specimens were then carried out under 800 °C and 160 MPa. The creep deformation and fracture behaviors were further investigated through interrupted creep tests. During the PBHT procedure, microstructure evolution of the joint occurred with creep life prolonged from 64 h to 368 h. The superdislocations in TLP and TLP + PBHT specimens were determined to study the γ′ phase shearing modes. Both individual superdislocations and APB-coupled partial dislocation pairs are observed. The variation of dominate superdislocation configurations among different joint zones and the evolution of the superdislocations during the creep process are discovered. Besides, the formation of different γ′ rafting microstructures and the initiation of intergranular microcracks in the polycrystalline joint are both studied.

Microstructural evolution during sintering of Fe-Cr-C steels prepared from admixed elemental powders

ABSTRACT In the upcoming years, a reduction in the use of critical elements, such as Ni and Cu, with unstable prices and high demand from the electromobility sector will become increasingly important for the PM-industry. Cr-alloyed sintered steels offer attractive properties at a moderate cost, but so far mostly Cr-prealloyed grades have been used. This work analyses the microstructural homogenisation process when Cr is introduced as admixed elemental powder. It is shown how – due to its high carbon affinity – Cr particles act as ‘internal carbon-getters’. There is an intermediate ‘heterogenization’ of the microstructure, i.e. the iron matrix is decarburised due to the formation of (Cr, Fe)-carbides. Final homogenisation depends on the formation of a transient liquid phase through the eutectic reaction between carbides and the iron matrix. Thus, the microstructure is not only sensitive to aspects such as sintering temperature or Cr-particle size but also to the heating rate and small variations in nominal carbon.

Effect of Rb2CO3 and Cs2CO3 on MgB2 in polycrystalline bulk samples

MgB2 polycrystalline bulk samples were prepared by means of reaction of Mg and B powders mixed with various amounts of Rb2CO3 or Cs2CO3 powders. The a-axis lattice parameter is decreasing in parallel with the increase of the carbonate addition level, more in the case of Cs2CO3 than Rb2CO3, while the c-axis parameter marginally increases. The extent of the a-axis contraction appears to be larger than expected from carbon doping only. The superconducting transition temperature of MgB2 decreases upon addition of the carbonate compounds. EDS analysis shows that some Cs and maybe Rb are still present in the samples after reaction. Whereas no evidence was found for segregation of these elements in impurity phases, it is not possible to ensure that Rb and/or Cs actually enter the MgB2 lattice due to the low amounts used in this study. The critical current density of MgB2 was improved both in self field and under low applied magnetic field for T ≤ 30 K, with optimum results for 1 mol.% Rb2CO3 addition and 1 mol.% Cs2CO3 addition respectively. The absolute value of the pinning force is hardly improved. The flux pinning mechanism at low field is similar for all samples and corresponds to the point pinning model behavior but at reduced fields b > 1 the pinning force dependence points towards an increasing contribution of surface pinning. This indicates that the jc improvement at low fields is due to other effects than enhanced flux pinning. It is possible that Rb2CO3 and Cs2CO3 induce a transient liquid phase during the reaction between the Mg and B powders, which improves the crystallinity and thus the critical current density at low field.

Intermetallic compound evolution and mechanical properties of Cu/Sn58Bi/Cu 3D structures blended with B4C nanoparticles during isothermal aging

The Cu/Sn58Bi/Cu and Cu/Sn58Bi-0.6B4C/Cu joints were prepared by transient liquid phase (TLP) bonding technology to verify the reliability of low-temperature connection joints. Intermetallic compound (IMC) evolution at the interface under different isothermal aging times was analyzed, and the mechanical properties of the joints were tested. The results show that two kinds of IMC, lamellar Cu3Sn and fan-shaped Cu6Sn5, are formed on both sides of the joint. With increasing soldering time, the thickness for both kinds of IMC become thicker, and it is significantly thicker for the IMC near the cold end. Furthermore, the IMC growth rate of the Cu/Sn58Bi-0.6B4C/Cu solder joint is significantly lower. When the isothermal aging time reaches 36 h, the Cu/Sn58Bi/Cu joint has been almost composed of IMC, while it needs a longer time for the Cu/Sn58Bi-0.6B4C/Cu joint. The growth of Cu3Sn IMC is in line with parabolic law, being mainly controlled by volume diffusion near the hot end, while the grain boundary diffusion significantly affects it at the cold end. The joints shear strength decreases gradually with extending bonding time, but it is always higher for the Cu/Sn58Bi-0.6B4C/Cu joint. When the heating time is not long, the fracture mainly appears at the Bi-rich phase in the solder matrix. With increasing bonding time, the location of fracture gradually transformed from the Cu6Sn5 grains to the junction of the two IMC and Cu3Sn grains, along with the intercrystalline fracture and transcrystalline fracture. In summary, B4C nanoparticles can significantly improve the joint reliability and enhance its mechanical properties.