Power Electronics Packaging Research Articles

Al-clad Cu bond wires for power electronics packaging: Microstructure evolution, mechanical performance, and molecular dynamics simulation of diffusion behaviors

With the advancement of power electronics, aluminum-clad copper thick bonding wires have garnered attentions due to superior electrical and thermal properties, making them well-suited for high-temperature and high-current applications. However, the impact remains unveiled of whether the growth of intermetallic compounds (IMCs) at the bonding interface presents critical challenges to the reliability of wedge wire bonds. Therefore, it is necessary to investigate the evolution behavior of Cu/Al IMCs in Al-clad copper wires. In this study, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were firstly employed to characterize the phase composition and growth behavior of Cu/Al intermetallic compounds (IMCs) at two distinct interfaces—the bonding interface and the core-shell interface—under various annealing conditions during high-temperature storage (HTS) tests, revealing a parabolic relationship between aging time and IMCs thickness. Subsequently, shear and pull tests of Al-clad copper bond wires were conducted to evaluate the bonding strength under different aging conditions, clarifying the correlation between various failure modes of the bonds and the evolution of IMCs at the bi-interfaces of this novel composite across different aging stages. Additionally, molecular dynamics (MD) simulations were employed to explore the diffusion behavior of Cu and Al atoms. It revealed that polycrystalline structures enhanced the mutual diffusion at the interface, with copper serving as the predominant element in the interdiffusion process. In conclusion, this study integrates experimental and numerical approaches to elucidate the growth mechanisms of Cu/Al intermetallic compounds and their effects on reliability, providing valuable guidance for optimizing the performance of composite bonding wires in high-temperature power device applications.

Ag-Pd nanoalloy film with ultra-high thermal and electrochemical stability for power electronic packaging

Nano-Ag paste is a popular material in power electronic packaging, while its microstructure is unstable at high temperatures and suffers from electrochemical migration. In this work, Ag-Pd nanoalloy film has been prepared by the pulsed laser deposition, and been sintered at low temperature for packaging. The thermal stability is significantly improved at 300 ℃ when Ag is alloyed with Pd. The Pd addition significantly increased the diffusion activation energy of Ag atoms and reduced the diffusion coefficient. The Ag-Pd sintered layer exhibited a stable microstructure at 300 °C or even 500 °C, which indicated that Ag-Pd nanoalloy had the potential to serve at high temperatures. Ag-Pd nanoalloy will preferentially generate a PdO passivation film and cover the anode surface, thereby slowing down the dissolution of the Ag and improving its resistance to electrochemical migration. This work provides theoretical studies and insights into the applications of Ag-Pd nanoalloys in high-reliability power electronics.

Reliability Simulation of IGBT Module with Different Solders Based on the Finite Element Method

The interconnecting solder is a key control factor for the reliability of electronic power packaging because it highly affects the junction temperature of insulated-gate bipolar transistor (IGBT) modules and is prone to plasticity, creep, and other failure behaviors under temperature-change environments. In this paper, the interconnecting performance and fatigue life of five different kinds of solders such as SAC305, sintered silver, Au80Sn20, sintered copper, and pure In under direct current (DC), power cycle, and electro-thermal coupling complex environments were studied based on electro-thermal multi-physical field coupling finite element simulation method, respectively. Results show that the sintered silver owns the most outstanding thermal reliability and the DC operating junction temperature of the IGBT module after utilizing sintered silver solder is only 90.2 °C, which is nearly 15 °C lower than that of the IGBT module utilizing SAC305 solder. Furthermore, in the power cycle reliability test, the fatigue life of Au80Sn20 solder reaches a maximum of 3.26 × 107 cycles while the life of indium presents only 5.85 × 103 cycles, a difference of nearly four orders of magnitude. Finally, under the complex environment of electro-thermal coupling, the fatigue life of Au80Sn20 solder is also the largest at 1.9 × 106 cycles, while the smallest life of solder becomes SAC305 solder at 4.44 × 102 cycles. The results of this paper can provide a theoretical basis for solder selection and life prediction of the IGBT module, which is of great significance in improving the reliability of power electronic packaging.

Silicon carbide nanowire-reinforced micro-Ag joint based on pinning effect for power electronics packaging

Low-temperature sintering Ag technology is a feasible approach employed in power electron devices. In this study, the influence of the different amounts (0, 0.03, 0.05, 0.07, 0.10, 0.20 wt%) of silicon carbide nanowires (SiC NWs) on the properties and microstructure of micro-Ag paste sintered at 250 °C without pressure has been investigated. The results exhibit that the bonding strength of the Ag-SiC joint reaches a maximum of 43.57 MPa after doping 0.07 wt% SiC NWs, with an increase of 13 % compared with pure Ag joint. This enhancement mechanism can be owed to the Orowan mechanism and the pinning effect of SiC NWs, which nail at grain boundaries that will restrain the dislocation motion of Ag grains. Meanwhile, the electrical resistivity of Ag-0.07SiC shows a minimum value of 5.20 μΩ cm, approximately 10.65 % lower than pure Ag joint. This is attributed to the well-sintered Ag network and the bridging effect of SiC NWs distributed in Ag particles. Thus, incorporating appropriate content of SiC NWs into micro-Ag paste can strengthen the mechanical performance and electrical conductivity of sintered Ag joint. It is hoped that this research could develop a new micro-Ag paste with outstanding properties that could be employed in high-power electronic devices.

Rapid on-site nondestructive surface corrosion characterization of sintered nanocopper paste in power electronics packaging using hyperspectral imaging

Sintered nanocopper (nanoCu) paste, exhibiting excellent electrical, thermal, and mechanical performances, offers promise for interconnections in wide bandgap (WBG) semiconductors operating at higher temperatures. However, sintered nanoCu is prone to severe corrosion in environments containing H2S, with on-site characterization methods for the composition of corrosion products currently lacking. In this study, a novel method was proposed for the rapid characterization of corrosion products during the corrosion process based on hyperspectral imaging (HSI) technology. Sintered nanoCu samples were subjected to 336 h H2S gas corrosion tests with bulk Cu as the reference, followed by correlating the corrosion element content with hyperspectral characteristic parameters. Then, the morphology and composition of corrosion products were researched using focused ion beam scanning electron microscope (FIB-SEM) and transmission electron microscope (TEM) analysis. The results showed that (1) during the corrosion process, a linear relationship was established between the Cu, O elemental atomic contents on the sample surfaces and their hyperspectral characteristic parameters. (2) The elemental atomic content of S exhibited an exponential relationship with the characteristic parameter. (3) The change rate in the spectral characteristic parameters during the corrosion process reflected the severity of corrosion, which was confirmed by comparing the thickness of the corrosion products of the sintered nanoCu and bulk Cu. This study offers a foundation for the further investigation of rapid on-site characterization of sintered nanoCu corrosion involving H2S.

Facile synthesis of Cu-Sn nanoparticle film and its bonding mechanism for power electronic packaging

The Cu-Sn full intermetallic compound is a promising high-temperature electronic packaging material, while its preparation is usually time-consuming. In this work, a novel dual-beam laser co-deposition method was proposed to prepare Cu-Sn nanoparticle film for power electronic packaging with high bonding efficiency. Various Cu-Sn contents were prepared to reveal the bonding mechanism of the full intermetallic compound structure. The results show that joints with a Cu content ranging from 20 wt% to 80 wt% could form full intermetallic compounds within 2 min with the shear strength reaching 120 MPa. Specifically, Cu6Sn5, 'island-like' Cu3Sn, and sintered Cu generated successively in the bondline center with the increasing Cu content. All failures occurred within the bondline indicating a higher interface bonding quality, while the 'island-like' Cu3Sn enhanced the shear strength. This die attach process is compatible with current commercial SiC die attach process with lower material cost as well as high efficiency, enabling the Cu-Sn nanoparticle film to be a promising material for high-reliability power electronic packaging.

Thermal-structural Modeling of power electronic package: effects of deposition geometry and dry spot on the stress distributions

A Power Electronics package is a heterogeneous system made of semiconductor devices (dies), metallic-ceramic substrate, baseplate and encapsulating material.The electronic devices can be MOSFETs (Metal Oxide Semiconductors Field Effect Transistors), diodes, IGBTs (Insulated Gate Bipolar Transistors) and passive components such as capacitors, resistors and sensors integrated on support circuit; the complete set of semiconductor devices installed on a package form the so-called “power modulus”.These devices play an important role in the transmission and conversion of energy in electric and hybrid vehicles. Due to the elevated currents and, consequently, the elevated temperatures at which these systems work, and due to the mismatch of the thermal-mechanical properties of the materials from which they are made, stresses and strains develop within the devices.Such stresses can be locally concentrated and amplified, depending on the deposition geometry of the various layers constituting the semiconductor device. Edge termination structures are essential to decrease the electric field at die’s edges, and, including brittle compounds in their composition, like Si3N4 or SiO, they are quite sensitive to mechanical stress.Another reason that may cause the stresses concentrations is the presence of dry spots. Dry spots are areas of various size, located at the interface between die or leadframe and the encapsulating resin, where there is a total or partial lack of adhesion.The aims of this work are, mainly, two. At first, four linear finite element analyses have been performed in order to evaluate the stresses concentrations at the corners of edge termination structure.The first case concerns sharp corners and the other cases concern differently filleted corners. In the second part of this work, it has been analysed the dry spot effect on stress distributions. Due to the small size of the defect with respect to the whole package, a Global-Local FEM approach has been used, creating a local subdomain where the mesh is denser than the global domain and a running a further separate numerical analysis which takes its boundary conditions from the global analysis, so delivering reliable small-scale stress and strain gradients. This approach permits to achieve accurate analyses focused on zones of interest of the global domain, limiting the increase of the computational cost of the modelling.

Microstructure evolution and micromechanical behavior of solvent-modified Cu–Ag composite sintered joints for power electronics packaging at high temperatures

With the increased deployment of power modules in demanding conditions, sintering materials, especially composite sintering materials, have raised growing interest due to their cost-effectiveness and suitability. Therefore, this study explores the viability of Cu–Ag composite sintering material, focusing on solvent influence through microstructure and mechanical behavior analysis. Micron-sized particle-based Cu–Ag composite pastes were designed and compared using eight solvents (four epoxy-free and four epoxy-added) based on fluidity and thermal stability. The sintered joints' performance, assessed through shear strength analysis, showed comparable values to pure silver sintering for both epoxy-free and epoxy-added samples. Optimized samples from each solvent system underwent reliability analysis, demonstrating that Cu–Ag joints with epoxy resin exhibited significantly higher shear strength after high-temperature storage and thermal cycling tests. Micromorphology and elemental composition analysis revealed differences in aging mechanisms, primarily attributed to variations in porosity due to oxide formation and pore filling by epoxy resin under different solvent systems. Further nanoindentation characterization of micromechanical properties, including hardness, modulus, and creep properties, during high-temperature aging, established constitutive models for insights into reliability evolution. In conclusion, the optimized epoxy-added Cu–Ag sintered joints proposed in this study demonstrated exceptional reliability and acceptable micromechanical properties, presenting a promising option for high-temperature power packaging.

Foreword: Special Section on Multiphysics Aspects of Power Electronics Packaging—Power Die, Power Module, and Converter Level—Part 1

Foreword: Special Section on Multiphysics Aspects of Power Electronics Packaging—Power Die, Power Module, and Converter Level—Part 1

A rapid-sintering Cu-Cu joints with ultrahigh shear strength and super reliability for power electronics package

Sintered Cu interconnection technology for power electronics has been widely investigated owing to its unique low temperature sintering high temperature service characteristics and price superiority. However, the currently research usually requires long sintering time (>30 min) and high pressure (>5 MPa). Here, we synthesized copper formate coated Cu nanoparticles (Cu-FA) by a solvothermal reaction, which can achieve rapid sintering at 260 °C with pressure of 5 MPa in 5 min to obtain robust joints of 67.41 MPa for fabricating SiC MOSFET devices. After 1000 h thermal aging and 1000 cycles thermal shock, the strength of joints can still maintained above 50 MPa. Moreover, SiC MOSFET modules were demonstrated using Cu-FA die attachment, which exhibit a 43.6 % lower thermal resistance compared to commercial Sn–Pb solder. Furthermore, copper paste performs better in long-term reliability. This paper provides an effective way to obtain high quality sintered Cu joints rapidly, which is suitable for the packaging of next generation power devices.

Infrared Radiation-Assisted Non-Pressure Sintering of Micron-Sized Silver for Power Electronic Packaging

In recent years, silver sintering has gained increasing attention in high-power density electronic packaging due to its characteristics such as a high melting point and excellent thermal and electrical conductivity. Micron-sized silver sintering offers a lower cost, but requires a longer processing time and additional pressure, which constrains its application. This paper presents a low-cost sintering process using infrared radiation (IR) as a heat source. By leveraging the unique properties of IR, the process achieves selective heating. The thermal energy can be mainly absorbed by the specific areas requiring sintering. This innovative approach eliminates the need for external pressure during the sintering process. This feature not only simplifies the overall process but also reduces the processing time required for sintering. The silver joints obtained from IR sintering process for 45 min achieved an average chip shear strength of 38 MPa at a temperature of 225 °C, which is higher than the strength of silver joints obtained from a traditional sintering process for 2 h. Additionally, the IR-sintered silver joints have a resistivity of 9.83 × 10−5 Ω·cm and scanning electron microscope (SEM) images of the joints reveal that the sintered joints obtained through the IR sintering process exhibit less porosity compared to joints obtained through a traditional sintering process. The porosity of the IR silver joints at 225 °C is 6.4% and does not change even after 3000 cycles of thermal shock testing, showing outstanding reliability. A GaN power device using IR silver joint also performed better in thermal and electrical performance testing, showing promising potential for the application of micro-silver paste in power electronic devices.

Online Condition Monitoring Methodology for Power Electronics Package Reliability Assessment

Online Condition Monitoring Methodology for Power Electronics Package Reliability Assessment

Review on Shear Strength and Reliability of Nanoparticle Sintered Joints for Power Electronics Packaging

Review on Shear Strength and Reliability of Nanoparticle Sintered Joints for Power Electronics Packaging

Preparation of Ag-Cu nanoparticle film using a dual-beam pulsed laser deposition for power electronic packaging

Ag-Cu nanoparticles, integrating the advantages of Ag and Cu, are promising materials for power electronic packaging. In this work, a novel dual-beam pulsed laser deposition method was proposed to prepare an Ag-Cu nanoparticle film with various component ratios and used for die attach at low temperatures. The as-deposited Ag-Cu nanoparticle film was mainly composed of Ag-Cu solid solution, Ag element, and Cu element, and most of the nanoparticles were in the alloying state. The Ag-Cu sintered joint presented a dense microstructure with 10.8% porosity, and the shear strength of Ag-Cu sintered joints could reach 60 MPa at 250 °C. The sintered joint porosity increased as more Cu were added in the Ag-Cu nanoparticle film, resulting in a decrease in the interfacial connection ratio. The fracture mode of sintered joints gradually changed from the sintered layer to the mixed sintered layer and interface fracture. The dual-beam pulsed laser deposition method could guide in designing the component ratios of bimetallic nanoparticles.

Sintering Mechanism of Bimodal-Sized Cu Nanoparticle Paste for Power Electronics Packaging

Sintering Mechanism of Bimodal-Sized Cu Nanoparticle Paste for Power Electronics Packaging

Interface regulation of micro-sized sintered Ag-10Al composite based on in-situ surface modification and enhanced microstructure stability in power electronic 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 Ag2O/Al2O3 amorphous/Al structure. This structure was formed through the Ag nanoparticle jetting effect of Ag flakes, achieving effective bonding between nano Ag2O and Al2O3 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.

Microscopic fracture toughness of notched porous sintered Cu micro-cantilevers for power electronics packaging

To fulfill the high-temperature application requirement of high-power electronics packaging, Cu nanoparticle sintering technology, with benefits in low-temperature processing and high-melting point, has attracted considerable attention as a promising candidate for the die-attach interconnect. Comprehensive mechanical characterization of the sintered layer at a microscale is necessary to deepen the understanding of the fracture behavior and improve the reliable design of materials. In this study, microscale cantilevers with different notch depths were fabricated in a 20 MPa sintered interconnect layer. Continuous dynamical fracture testing of the microcantilevers was conducted in situ in a scanning electron microscope to detail the failure characteristic of the porous sintered structure. The microscopic fracture toughness of different notched specimens was obtained from the J-integral in the frame of elastic-plastic fracture mechanics. Specimens with deeper notches presented higher resistance to crack extension, while geometry factors of notch-to-width ratio between 0.20 and 0.37 exhibited a relatively stable microscopic fracture toughness ranging from 3.2 ± 0.3 to 3.6 ± 0.1 MPa m1/2.

One-Probe Nanoprobing of Power Devices and Electronic Packages

Results involving the use of a single nanoprobing contact are presented, on both a SiC planar MOSFET device, and a small system-in package. In both cases, mechanical polished samples were prepared, and then probed with a single contact. For the SiC MOSFET, the depletion zones were imaged while the samples were mounted on a 45 ° stub. Discussion of the different signals generated from Passive Voltage Contrast (PVC) and Electron Beam Induced Current (EBIC), as well as possible artifacts of sample grounding, are provided. For the package, Electron Beam Absorbed Current (EBAC) provided indication of connected features within the sample. The experiment showed the capability of measuring features across three orders of magnitude in size.

Study on thermal conductivity of micron BN-nano SiO2 combined modified epoxy resin composites

Epoxy resin has attracted widespread attention in the field of power electronic packaging due to its favorable processing technology, high adhesion, and excellent dielectric properties. The enhancement of thermal conductivity in epoxy resin through the incorporation of diverse particles is a prominent area of interest in the realm of modified insulation materials. In this study, hexagonal boron nitride (h-BN) and silicon dioxide (SiO2) with good thermal conductivity were used as doped fillers to modify epoxy resin (EP). The analysis of experimental results indicated that the thermal conductivity of materials with a total doping amount of 20 wt% and a mass ratio of BN to SiO2 of 70:30 to 60:40 could increase the thermal conductivity by 118.1~126.0%. In contrast to pure EP, the thermal conductivity of composite epoxy resin materials has been significantly enhanced.

Interfacial bonding mechanisms of sintered Cu nanoparticles on different metallization surfaces

Cu nanoparticle sintering bonding is a low-cost die-attach method compared with Ag nanoparticles for power electronic packaging. The joint strength highly depends on the surface metallization of the devices. In present study, the interfacial sintering behavior of copper nanoparticle film (CNF) on different metallizations (Au, Ag, and Cu) was studied. The CNF exhibited a superior shear strength (115 MPa) on Cu substrates when sintered at 250 °C-15 MPa, much higher than that on Ag and Au metallized substrates. The interface connection ratio of bondline-substrate showed the same trend as the shear strength. The neck formation at the bonding interfaces showed no orientation preference. The lateral diffusion of Cu atoms on substrates dominated the sintering bonding, rather than the longitudinal diffusion. The Cu metallization showed much faster lateral diffusion than the Ag and Au metallization, which was confirmed by the neck growth of monolayer nanoparticle sintering and the molecular dynamics (MD) simulation.