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Owing to its cost-effectiveness and low coefficient of thermal expansion (CTE), micron Si is incorporated into sintered Ag matrix to develop an Ag@Si composite sintering strategy. The Si integration helps reduce cost and alleviate CTE-mismatch of Ag-sintered die attachments. An innovative Ag@Si composite sintering structure is achieved by low-temperature and pressure-less sintering process, where a possibly slight diffusion of native SiO 2 on the Si surface toward Ag is indicated by TEM observation, enabling the integration of Ag and Si into one continuous network. Owing to the robust well-bonded composite sintering, the Ag@Si joining strategy provides mechanical/microstructural reliability far beyond the pure Ag sinter joining, demonstrating significant prospects in high-temperature interconnection applications. During the harsh thermal cycling (−50–250 °C), the mitigating effect of the Si addition on CTE mismatch is manifested through the substantial suppression of microstructure deterioration in Ag@Si joint that occurs in pure-Ag-sintered joint, while the shear strength retention rate is doubled. Detailed investigation into the mechanism for elevated performance was conducted by material property and Missies stress analysis. The incorporation of Si helps modify the CTE, elastic properties, and stress distribution of Ag@Si-sintered material, synergistically contributing to the satisfactory joining reliability. [Display omitted] • The Ag@Si composite sinter joining was developed for power modules, where Si addition not only contributed to cost reduction but also helped alleviate CTE-mismatch issues in modules. • The Ag@Si sintering was revealed to be a well-integrated network between Ag and Si due to the slight diffusion of native SiO 2 on Si, offering good mechanical stability for the composite joining layer. • The integrated matrix endows Ag@Si sinter joint with much superior reliability to pure Ag sintered joining, both in terms of mechanical and microstructural stability during thermal cycling. • The impact of Si addition on alleviating CTE-mismatch was systematically validated through analyses of thermal expansion, tensile properties, and finite element method (FEM) simulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrafine Ag nanoparticles ejection phenomenon of micron Ag flake is observed for the first time by in-situ TEM. • In-situ surface modification of Al particles in sintered Ag-Al composite is completed via Ag nanoparticles ejection phenomenon. • A specific Ag/nano Ag 2 O/Al 2 O 3 amorphous/Al composite interface structure was formed via mutual dissolution at the atomic level. • Shear strength of sintered Ag-10Al joint reached 34.1 MPa after 1000 h aging, meeting the requirements for power semiconductor packaging. The increasing demand for high-power SiC semiconductors necessitate the development of a die attachment material that combines high-temperature resistance, reliability, and cost-effectiveness. In this study, a novel micro-sized composite, Ag-10Al paste, containing 10 wt% Al particles, was designed. A remarkable phenomenon, the ejection of ultrafine Ag nanoparticles from micron-sized Ag flakes, was observed for the first time. The phenomenon was utilized for the in-situ surface modification of Al. Subsequently, the microstructure and mechanical properties of the sintered Ag-10Al/direct bonded copper (DBC) joints were studied. Results indicated that the Ag-10Al composite exhibited superior microstructure stability compared to sintered Ag. The Ag/Al interface was systematically analyzed, revealing a unique Ag/nano Ag 2 O/Al 2 O 3 amorphous/Al structure. This structure was formed through the Ag nanoparticle jetting effect of Ag flakes, achieving effective bonding between nano Ag 2 O and Al 2 O 3 amorphous phases through mutual dissolution at the atomic level. Moreover, the sintered Ag-10Al joint demonstrated enhanced mechanical performance stability over the sintered Ag joint. After 1000 h aging at 300 ℃, the shear strength of the sintered Ag-10Al joint reached 34.1 MPa, meeting the requirements for power semiconductor packaging. In conclusion, the Ag-10Al composite paste was thoughtfully designed, excelling in both performance and cost-effectiveness. [ABSTRACT FROM AUTHOR]

We investigate the role of an Ag interlayer to suppress Kirkendall void formation in Ti/Ni surface finishes on the die-attached joints during harsh thermal aging tests at 250 °C. GaN dies were attached to the Ti/Ag/Ni sputtered direct bonded aluminum (DBA) and Ti/Ni sputtered DBA substrate using a high-temperature soldering, respectively. Without the Ag interlayer, void size increased to 0.69 µm after 1000 h of aging, but with the Ag interlayer, it reduced to 0.0794 µm. The Ag interlayer retards the development of cracks and void coalescing by controlling the diffusion rate between Ni/Sn at the bonding interface during thermal aging. • Analyzing how a silver interlayer affects Ni-finished GaN power semiconductors in in-wheel motor integration. • Quantifying the link between mechanical capabilities and microstructure in crystallographic characteristics. • Exploring how the Ag interlayer controls Ni-Sn IMC system diffusion rates. [ABSTRACT FROM AUTHOR]

Interface connection of sinter micron-sized Ag paste on Cu substrate in a low temperature pressure-less condition was improved by a novel 3D pyramid-shape Ag plating layer which possessed a larger surface area four times than that of a Ag flat plating. Interface connection ratio achieved to 65% corresponding to a satisfied interface bonding strength of 25.3 MPa at 180 °C pressure-less sintering. Finite element model for sinter Ag joining on the 3D pyramid-shape Ag plating was constructed and revealed that stress mainly concentrated at Ag plating protrusions but not at the interface bonding line like the Ag flat plating case. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The need for power modules has been promoted by the emergence of electric vehicles. The requirements of small volume, high integrity, and high reliability for the next-generation power module lead to the change of encapsulation method from previous gel encapsulation to epoxy encapsulation. Efforts have been made to enhance epoxy materials, and commercialized high-end epoxy has shown excellent properties, but power module failures still exist. The possible reason may lie in the interfacial interaction between encapsulation epoxy and substrate, which is less noticed previously. This paper seeks to unveil the influence of interfacial interaction on the bonding reliability between encapsulation epoxy and copper substrate. Three reliability tests were performed: high-temperature storage test (HST), temperature cycling test (TCT), and pressure cooker test (PCT). The bonding strength after these reliability tests was evaluated, and the bonding interface and fracture surface were analyzed in a nanoscale. Our study discovered that interfacial interaction plays a vital role in encapsulation reliability. Copper can diffuse into the epoxy and catalyze epoxy thermal oxidative degradation, which results in bonding strength reduction after HST and PCT. The surface structure change caused by copper oxidation after HST and PCT also reduced the bonding strength. These findings will greatly benefit future power module design. • The influence of interfacial interaction on the copper/epoxy bond reliability was studied. • Three reliability tests, high-temperature storage test, temperature cycling test, and pressure cooker test, were studied. • All the reliability tests were conducted according to the requirements of the next-generation SiC power module. • The bonding interface and fracture surface were analyzed on a nanoscale. • Copper diffusion into epoxy and copper-catalyzed degradation of epoxy under high temperature were identified. [ABSTRACT FROM AUTHOR]

Abstract Solid-state porous Ag was utilized to achieve interface bonding under low temperature and low-pressure for large area, high-reliability designs for high performance die-attach power modules in high temperature applications. In this process, solid-state porous Ag was first fabricated by sintering Ag particles onto both a Cu substrate and an Si die with different bonding areas. After polishing the surface of the solid-state porous Ag, the Ag-Ag interface was bonded together under low pressure (0.4 MPa) and low temperature (250 °C and 300 °C). The bonding strength was greater than 30 MPa for a 15 mm x 15 mm bonding area at a bonding temperature of 300 °C. The electrical resistivity of the solid-state porous Ag was about 7 µΩ cm, or half that of Pb-free alloy solder materials. The bonding mechanism of the Ag-Ag interface was analyzed by a transmission electron microscope. It was observed that Ag hillocks and nanoparticles had been generated and bridged the Ag-Ag interface. This resulted in a large interface connection ratio and a high bonding strength. In addition, it was observed that the shear strength of the solid-state porous Ag with a thick bonding layer decreased thermomechanical stress in the die-attached power module and thus improved structural reliability. This bonding process featuring solid-state porous Ag presents an attractive technology for the fabrication of large area bonding and high-reliability die-attached module structures for high temperature applications. [ABSTRACT FROM AUTHOR]

Abstract This work firstly evaluated the microscale mechanical properties of sintered Ag, consisting of various Ag particles of a flake shape and spherical shape from nano to micro size. Microscale pillar specimens were fabricated by a focused ion beam process and the mechanical properties of the sintered Ag, were measured by micro-compression testing using a nano-indentation system. The microstructure of sintered Ag is dependent upon the size and the shape of the utilized Ag particles, as this significantly influences its fracture behavior and mechanical properties. Mechanical properties not only depend on the porosity of the sintered Ag, but also on the degree of necking growth of the Ag particles. To explore this further, the shear strength of Ag sinter joint using different sizes and shapes of Ag particles was also evaluated. This revealed that sintered Ag flake particles possess a much greater bonding strength above 30 MPa than do sintered Ag spherical shape particles from nano to micro sizes. TEM observation revealed that many nanoparticles with a size less than 10 nm were formed in the sintered Ag flake structure due to its high grain boundary density and dislocation density, which increased its grain bonding quality. Graphical abstract Unlabelled Image Highlights • Microscale mechanical properties of sintered Ag particles with a different size and shape were evaluated. • Mechanical properties of sintered Ag depend not only on its porosity, but also upon the necking growth. • Sintered Ag flake particles have a much better bonding strength above 30 MPa than sintered Ag spherical shape. • The self-generated Ag nanoparticles from sinter Ag flake, improve the necking growth of Ag particles. [ABSTRACT FROM AUTHOR]

Corrosion mechanism of Zn-30Sn high-temperature, lead-free solder in neutral 0.5 M NaCl solution are investigated by using FE-SEM, XRD, XPS and SIMS. The results confirm that α-Zn phases are corroded preferentially. Moreover, during initial corrosion process, a double-layer structure of ZnO and Zn(OH) 2 is formed, providing beneficial barrier effect hindering the penetration of Cl − . However, subsequent morphology transformation weakens barrier effect to Cl − penetration and results in severe corrosion. Mechanism of surface layer breakdown and internal corrosion propagation are further examined, where it is determined that aggressive Cl − plays an important role in the corrosion process of Zn-30Sn solder. [ABSTRACT FROM AUTHOR]

A bonding technology is introduced by using surface polished porous Ag in die-attachment structure. Bonding strength did not change much as the chip size varied from 3 × 3 mm 2 to 15 × 15 mm 2 . This confirms that the technology was not influenced by the chip size, and thus can be used in large area bonding. Bonding mechanism based on stress-induced migration was discussed with the three dimensional finite element analyses. Transmission electron microscopy (TEM) observation further confirmed that single crystal hillocks and Ag particles formed at the bonding interface, bridging the interface together. [ABSTRACT FROM AUTHOR]

The fast development of electric vehicles promoted the development of next-generation power modules. Along with this trend, the encapsulation techniques are also transforming from previous gel encapsulation to epoxy encapsulation because epoxy encapsulation reduces the module size significantly. However, the dissimilar bonding between the epoxy and the metal substrate is a weak part of the entire module. Unlike previous studies, which focused on epoxy properties and thermal stress, we investigated the failure mechanisms between the encapsulation epoxy and the copper substrate under high temperatures by considering the interfacial interaction. A high-temperature storage test (HST) was performed at 200 °C until 1000 h for encapsulated packages. We then measured the bonding strength and identified the fracture path at the nanoscale by SEM, XPS, and ToF-SIMS depth profiling. In addition, the changes in the epoxy were characterized by ATR-FTIR, nanoindentation, and XPS depth profiling. The bonding interface was analyzed with AFM-IR, SEM, EDS, and STEM. We found that the fracture happened inside the epoxy rather than the copper/epoxy interface. More importantly, we found that copper atoms diffused into the epoxy reaching approximately 100 nm. The diffused copper atoms and the long-time high-temperature heating promoted the epoxy pyrolysis, forming a 100 nm thick weak layer at the epoxy side, which is the key reason for the high-temperature failure. Our study provided a fresh understanding of the failure mechanisms of the bonding between encapsulation epoxy and the copper substrate under HST, which will contribute significantly to future power module design and material development. • The failure of the epoxy encapsulation under the condition required by next-generation power modules was investigated. • Failure mechanisms of the interface between epoxy and metal substrate exposed to high temperature were revealed. • The copper diffused into epoxy under high-temperature aging, reaching approximately 100 nm on the epoxy side. • Under a long-time high-temperature condition, the diffused copper promoted the pyrolysis of the epoxy. • The weak layer caused by pyrolysis is the key reason for the failure of the epoxy encapsulation under high temperature. [ABSTRACT FROM AUTHOR]

The application of microporous sintered silver (Ag) as a bonding material to replace conventional die-bonding materials in power electronic devices has attracted considerable interest. Characterization of the mechanical properties of microporous Ag will enable its use in applications such as lead-free solder electronics and provide a fundamental understanding of its design principles. However, the material typically suffers from thermal and mechanical stress during its production fabrication, and service. In this work, we have studied the effect of microporous Ag specimen size on fracture toughness from the microscale to the macroscale. A focused ion beam was used to fabricate 20-, 10- and 5-μm-wide microscale specimens, which were of the same order of magnitude as the pore networks in the microporous Ag. Micro-cantilever bending tests revealed that fracture toughness decreased as the specimen size decreased. Conventional middle-cracked tensile tests were performed to determine the fracture toughness of the macroscale specimens. The microscale and macroscale fracture toughness results showed a clear size effect, which is discussed in terms of both the deformation behavior of crack tip and the influence of pore networks within Ag with different specimen sizes. Finite element model simulations showed that stress at the crack tip increased as the specimen size increased, which led to larger plastic deformation and more energy being consumed when the specimen fractured. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crack-less and deformation-resistant electroplated Ni/electroless Ni/Pt/Ag metallization layers for Ag-sintered joint was developed. • Three kinds of metallization layers on DBC substrate was designed and evaluated during thermal shock test (TST). • The Ag joint structures on different metallization layers exhibited different mechanical behaviors during the harsh TST from −50 ℃ to 250 °C. • Electroplated Ni/electroless Ni/Pt/Ag provided a stable shear strength, in addition to good microstructural maintenance for the Ag-sintered joints. • A thickened Ni layer is expected to suppress the thermal stress and the Ag layer is expected to enhance sinterability with the Ag paste. Aiming for a suitable die-attached substrate for Ag-sintered joint technology during harsh operating environment, three surface finishes of sputtered Ti/Ag- layers, electroless Ni-/Pt-/Ag- layers, and electroplated Ni-/electroless Ni-/Pt-/Ag- layers were developed to directly bond copper (DBC) substrates, denoted as Ti/Ag, ENPA, and E-ENPA, respectively. The effect of the metallization layers by three deposition technologies on the Ag joint structures was systematically investigated during an extreme thermal shock test (TST) ranging from −50 to 250 °C. The mechanical behaviors and interface evolution considerably varied depending on the metallization layer used. Both ENPA and E-ENPA substrates provided a more robust initial shear strength of approximately 60 MPa. More importantly, both metallization layers were productive in restraining interfacial deformation owing to the effect of the thick Ni plating. A better performance was derived from the electroplated Ni in E-ENPA metallization with crack-less and deformation-resistant, because of electroplated Ni possessed a suitable hardness and toughness, thus the optimal stress-relaxation capability. This study provides insights to the properties of Ag-sintered joints on three metallization layers, where the metallization, mainly by electroplating, exhibited superior reliability beyond that of sputtered and electroless depositions in both strength and microstructure maintenance. [ABSTRACT FROM AUTHOR]

A specimen size effect on the adhesion strength of Cu/insulation layer interface was studied by means of a new elastic–plastic finite element simulation technique. By considering the influence of the plastic zone at the interface crack tip, the adhesion strength appeared almost independent of the specimen size. Since the Cu crystals were far smaller than the specimen dimensions and thus no significant difference should be expected in adhesion strength, it is speculated that an accurate estimation of the plastic zone is essential for micro-scale specimen evaluation. [ABSTRACT FROM AUTHOR]

In this work, we applied a Ag flake formed paste for sinter-joining on bare Si, SiC, and GaN surfaces. The sintered joints possess a high shear strength of over 40 MPa under a pressureless sintering condition at 250°C. The high bonding strength of the joints is achieved by a tight adhesion between Ag and bare surfaces, which attributed to an excellent sinter-joining ability of the Ag flake. The flakes, acquired by mechanical milling, can be rapidly sintered into a homogenous porous structure at a pleasureless and low-temperature sintering condition due to its dislocation-rich nano grain structure. During sintering, a drastic morphology reconstruction of Ag flake, from a flattened flake to a drop-like particle, can introduce robust interfacial connection structures, which is important for the robust bonding. This Ag flake paste can be regarded as a promising sinter-joining material for the connection of bare surfaces in high-temperature applications. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper proposes a method to prepare aluminum nitride (AlN) ceramic–metal joints by nano-grained Ag flake particle sintering under low temperate pressure-free conditions. A robust shear strength larger than 25 MPa was achieved at 280 °C sintering for 3 mm × 3 mm joints. Moreover, large chip (5 mm × 5 mm, 10 mm × 10 mm) bonding confirmed that the technology was not influenced by the size and can be applied to large-scale ceramic–metal joining. Further investigation confirmed that nano-grained Ag micro flake particles were easily necked together, and the AlN/Ag interface could be tightly bound at a low temperature of 180°C. This study provides a new method for low-temperature pressure-less conditions for bonding ceramic-metal structure materials on a large-scale. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This study systematically investigates the effect of oxygen on the microstructural evolution as well as the macro/micromechanical characterization of Ag sinter paste during the aging process at 250 °C for 1000 h. The sintered Ag joint is separated into two groups and, respectively, kept in air and vacuum (10−4 Pa) atmospheres. The microstructure of sintered Ag paste become clearly coarsened after aging at 250 °C in air for 100 h, while it remains almost the same as in the initial state in vacuum, even after aging for 1000 h. The different microstructural evolutions are investigated in detail by transmission electron microscopy, which reveals that coarsening are involved in the Ag-O reaction and form a large number of Ag nanoparticles around sintered Ag particles, as well as enhance coalescence. Furthermore, the macro/micromechanical properties of sintered Ag paste, after aging in air and vacuum atmospheres, are evaluated by a die shear test and a nano-indenter system with a spherical diamond tip. Shear strength and fracture mode were systematically analyzed. The micromechanical properties of sintered Ag paste, including Young's modulus and hardness, depend on its microstructure and are largely influenced by its porosity, which decreases from initiation to 250 h and recovers after aging for 500 h in air. However, there is almost no change during the aging process in the vacuum atmosphere. The results of this study contribute to a better understanding of the microstructural evolution and the mechanical properties of sintered Ag joints, including the change in bonding quality and Young's modulus during aging for actual power modules, which are packaged by a resin. Image 1 • Oxygen effect on the microstructural evolution and mechanical properties of Ag sinter paste were investigated. • Microstructure of Ag sinter paste become coarsening in air aging but almost not any change in vacuum aging. • Coarsening behaviors maybe mainly caused by Ag-O reaction but not the self-diffusion kinetics of Ag atoms. • In-suit formation of Ag nanoparticles played a crucial role in the coarsening behaviors of Ag sinter paste. • Micromechanical properties of Ag sinter paste depend on its microstructure and influence by aging atmosphere. [ABSTRACT FROM AUTHOR]

Robust bonding and thermal-stable sinter Ag joining on an Au finished substrate was first time achieved for use in SiC power modules. Five kinds of Ag paste, including different solvents and Ag fillers, and four kinds of Au plating processes (ENIG, ENIGEG, ENEPIG and ENEPIGEG) were used to optimize the initial shear strength of Ag–Au joints. Here, EN means electroless Ni plating, EP means electroless pure palladium plating, IG means immersion gold plating process and EG is the process of electroless gold plating. Micro-scaled Ag flake paste showed the best die shear strength at 33.9 MPa by in-suit formation of Ag nanoparticles, accomplished with a sintering temperature of 250 °C without pressure in air. With the use of Electron backscatter diffraction (EBSD) analysis, the ENEPIG plating process exhibited an Au surface with greater Au (111) grain orientation and larger grain size, which both of that benefits bonding with Ag paste. The thermal-stable sinter Ag joining on ENEPIG was evaluated by aging at 250 °C up to 1000 h. The shear strength had slightly increased to 36.5 MPa after 1000 h. The mechanism of robust bonding and thermal-stable during high temperature aging were systematically analyzed via Scanning Electron Microscope (SEM), Energy dispersive X-ray spectroscopy (EDS), Transmission Electron Microscope (TEM) and X-ray diffraction (XRD), which was attributed to the large Au grains size, the favorable surface condition of the ENEPIG, and the Pd barrier layer which prohibited Ni diffusion into the Au layer during sintering and aging. Image 1 • Shear strength of sinter Ag–Au joints achieved to 33.9 MPa at 250 °C without pressure sintering in air. • In-suit formation of Ag nanoparticles improved the necking growth of sintered Ag. • ENEPIG plating shows a larger ratio of Au (111) grain orientation and bigger Au grains size. • Shear strength of sinter Ag–Au joints increased at 250 °C aging for1000 h. • Robust bonding and thermal-stability were attributed to less grain boundary diffusion and the Pd barrier layer. [ABSTRACT FROM AUTHOR]