Power Device Packaging Research Articles

Thermal decomposition temperature-dependent bonding performance of Ag nanostructures derived from metal–organic decomposition

In wide-bandgap semiconductor power device packaging, die bonding refers to attaching the die to substrate. Thereby, the process temperature of Ag sintering for the die bonding should be low to prevent damage to fragile dies. Herein, an organic-free strategy using Ag nanostructures derived from the thermal decomposition of metal–organic decomposition (MOD) was proposed to achieve low-temperature bonding. Significant effects on bonding performance were determined by the thermal decomposition temperature, which in turn determined the organic content and sintering degree of Ag nanostructures. At a low thermal decomposition temperature of 160 °C, incomplete decomposition resulted in high organic content in the Ag nanostructures, causing large pores inside the Ag joints owing to the generation of gaseous products. Owing to the Ag particles with naked surfaces and wide size distribution, the Ag nanostructure obtained at 180 °C showed an excellent bonding performance, resulting in a high shear strength of 31.1 MPa at a low bonding temperature of 160 °C. As the thermal decomposition temperature was 200 °C, sintering among Ag particles increased the particle size, resulting in a reduction of surface energy and driving force for sintering. We think that uncovering this underlying mechanism responsible for the bonding performance will promote the application of Ag MOD in the die bonding of WBG power devices.Graphical abstract

Microstructure characteristics for improved thermal shock reliability of sintered Ag[sbnd]Al paste in SiC power module

To meet the harsh thermal shock (−50–250 °C) requirements of power device packaging, a novel sintered Ag-based die attach material based on the sustained release effect of Al was proposed. In this study, Al particles with natural core-shell structure covered with Al2O3 layer were selected as the ideal doping-phase, and micron Al particles doped sintered Ag composite paste (AgAl) was prepared. First, the microstructural evolution of sintered AgAl joints during thermal shock was studied. The results showed that Al particles effectively suppressed the cracks generation, which attributed to the sustained release effect of Al element. To clarify sustained release mechanism of Al, the interfaces evolution between Ag and Al particles was investigated. In the initial stage, Al was covered by the Al2O3 layer, preventing inter-diffusion between Ag and Al. As the thermal shock proceeds, the Al2O3 film was fractured, achieving direct contact between metal Al and Ag. Diffusion thus takes place. For the sintered Ag5Al joint, the shear strength was 17.3 MPa after 1000 cycles, which is 1.57 times that of pure sintered Ag joint. These results indicate the successful development of low-cost, high-reliability die attachment materials for use in harsh thermal shock environments.

Residual Stress and Warping Analysis of the Nano-Silver Pressureless Sintering Process in SiC Power Device Packaging.

Chip bonding, an essential process in power semiconductor device packaging, commonly includes welding and nano-silver sintering. Currently, most of the research on chip bonding technology focuses on the thermal stress analysis of tin-lead solder and nano-silver pressure-assisted sintering, whereas research on the thermal stress analysis of the nano-silver pressureless sintering process is more limited. In this study, the pressureless sintering process of nano-silver was studied using finite element software, with nano-silver as an interconnect material. Using the control variable method, we analyzed the influences of sintering temperature, cooling rate, solder paste thickness, and solder paste area on the residual stress and warping deformation of power devices. In addition, orthogonal experiments were designed to optimize the parameters and determine the optimal combination of the process parameters. The results showed that the maximum residual stress of the module appeared on the connection surface between the power chip and the nano-silver solder paste layer. The module warping deformation was convex warping. The residual stress of the solder layer increased with the increase in sintering temperature and cooling rate. It decreased with the increase in coating thickness. With the increase in the coating area, it showed a wave change. Each parameter influenced the stress of the solder layer in this descending order: sintering temperature, cooling rate, solder paste area, and solder paste thickness. The residual stress of the nano-silver layer was 24.83 MPa under the optimal combination of the process parameters and was reduced by 29.38% compared with the original value of 35.162 MPa.

Cu array fabrication: An environmentally sustainable approach through bicontinuous microemulsion differential electrodeposition for advanced power device packaging

BackgroundThe demand for high-power density packaging and integration processes for third-generation semiconductors, like silicon carbide (SiC), necessitates advancements beyond conventional Si-based packaging technologies. Cu-Cu direct bonding emerges as a promising alternative in semiconductor packaging. However, achieving Cu-to-Cu direct bonding with low-temperature, low-pressure, and short-time poses significant challenges. Transient Liquid Phase Bonding (TLP) offers a low-temperature joining solution, but prolonged reflow time hinders its wide applications. MethodsThis study introduces a novel strategy utilizing bicontinuous microemulsion (BME) electrodeposition to fabricate micron-sized Cu arrays, addressing these challenges in achieving Cu bonding. The core of Cu array manufacturing lies in the differential electrodeposition rate of Cu ions in the aqueous and organic phases. This principle is rooted in the excellent conductivity of the aqueous solution compared to the non-conductivity of the organic solution. Significant findingsWe elucidate the growth mechanism and validate a theory for achieving void-free optimal growth of Cu arrays within BME and compared the cross-sectional morphology and fracture modes of TLP solder joints with micron and nano Cu arrays. Furthermore, the ability to recycle the BME soft template aligns with green chemistry principles, offering a sustainable die-attach approach for third-generation semiconductor device packaging.

Enhancing thermal-mechanical performance of micron Ag/ZrW2O8 nanorod die-attach paste with low thermal expansion

Negative thermal expansion not only challenges the traditional lattice concept, but also provides new opportunities for regulating the thermal expansion coefficient and addressing the increasing reliability demands in power device packaging. In this study, ZrW2O8 nanorods were firstly introduced into the micron Ag paste via a facile low-temperature (≤300 ℃) low-pressure (<10 MPa) sintering. The pinning and negative thermal expansion mechanisms contributed by the homogeneously dispersed ZrW2O8 nanorods significantly mitigate the thermal expansion mismatch and suppress the microstructure deterioration in SiC power module, which was also verified by finite element (FE) simulation. The Ag@2%ZrW2O8 (2% of the total weight of Ag) specimen possessed outstanding long-term reliability with a die-shear strength of 29.63 MPa after 1000 thermal shock cycles from −50–250 ℃. The novel findings can be inspiring on interconnected material optimization and selection in electric packaging application as well as reliability evaluation in the service condition.

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.

A Study of Electroplated Nanoporous Copper Using Aberration-Corrected Transmission Electron Microscopy.

Nanoporous Cu foam is widely applied in many fields such as the packaging of electronic power devices. In this study, a sandwich-structured Cu-Zn eutectic alloy precursor composed of Cu0.53Zn0.47/Cu5Zn8/Cu0.53Zn0.47 is prepared through electroplating. The surface layer of the precursor, Cu0.53Zn0.47, has a flat surface with numerous grain boundaries, which effectively promotes its dealloying behavior. By contrast, Cu5Zn8 has a porous structure, which promotes the dealloying behavior at the center of the precursor. The dealloying of Cu0.53Zn0.47 is dominated by the coherent surface diffusion of Cu atoms, and the crystal lattice and orientation show no changes before and after dealloying. By contrast, the dealloying behavior of Cu5Zn8 requires the renucleation of Cu crystals; in this process, Cu atoms are transported to the surface of the layer by capillary forces to form clusters, which nucleate and grow.

Power Device Packaging Technology for Next Generation Railway Applications

Power Device Packaging Technology for Next Generation Railway Applications

Insulation and Reliability Enhancement by a Nonlinear Conductive Polymer-Nanoparticle Coating for Packaging of High-Voltage Power Devices

Insulation and Reliability Enhancement by a Nonlinear Conductive Polymer-Nanoparticle Coating for Packaging of High-Voltage Power Devices

A first-principles study of the mechanical and physical properties of Ni3Snx intermetallic compounds for high-temperature power device packaging

Ni–Sn intermetallic compound is a highly promising high-temperature packaging material for power devices, and it is very necessary to understand and control the physical and mechanical properties of Ni–Sn intermetallic compounds(IMCs). However, the current research mainly focuses on the rapid preparation of such packaging solder joints, and there is little research on the microstructure, physical and mechanical properties of alloys. In this study, the first-principle and quasi-harmonic Debye models were used to analyze the mechanical characteristics, electronic structure, thermal conductivity, and linear expansion coefficient of three IMCs (Ni3Sn, Ni3Sn2, and Ni3Sn4) of the Ni–Sn system. The results show that Ni3Sn has the highest modulus and fracture toughness and has the best elastic match with Ni. The welded joints of Ni/Ni3Sn/Ni structures can effectively prevent the generation of microcracks under the stress field. They're all mixed-bond compounds, according to the results of electronic structure simulations, and Ni3Sn4 has the most ionic and covalent bonds, so its fracture toughness is the lowest and its anisotropy tendency is the most significant. The thermal conductivity of Ni3Sn is the highest, the linear expansion coefficients of Ni3Sn and Ni3Sn4 are not significantly different, and they match well with the linear expansion coefficients of Ni.

Investigation of the Degradation Mechanism of SiC MOSFET Subjected to Multiple Stresses.

The performance requirements for power devices in airborne equipment are increasingly demanding, while environmental and working stresses are becoming more diverse. The degradation mechanisms of devices subjected to multiple stresses become more complex. Most proposed degradation mechanisms and models in current research only consider a single stress, making it difficult to describe the correlation between multiple stresses and the correlation of failures. Then, a multi-physical field coupling model based on COMSOL is proposed. The influence relationship between temperature, moisture, electrical load, and vibration during device operation is considered, and a three-dimensional finite element model is built to investigate the multi-stress degradation mechanism under multi-physical field coupling. The simulation results show that, compared with single-stress models, the proposed multi-stress coupled model can more accurately simulate the degradation process of SiC MOSFET. This provides references for improving the reliability design of power device packaging.

Fabrication of high reliability Cu joints at low temperatures using synergistic effect of organic composition for power device packaging

Fabrication of high reliability Cu joints at low temperatures using synergistic effect of organic composition for power device packaging

Effect of liquid metal enhanced Cu nano/micro particle paste on performance of Cu-Cu joints

Cu nano/microparticle pastes have garnered considerable research interest and investigation for their application in the packaging of power devices. However, their inherent porosity negatively affects joint performance. In this study, we addressed the issue of porosity in Cu-Cu joints by incorporating a liquid metal (LM) into a Cu nano/microparticle paste solder. The LM exhibits wettability and flowability, enabling it to spontaneously fill the pores in the Cu nano/microparticle structure and establish connections with the substrate surface. Moreover, the LM creates additional conductive pathways and reduces thermal resistance, resulting in enhanced electrical and thermal conductivities. The experimental thermal conductivity reached an impressive value of 342.68 W/(m·K), while the observed electrical resistivity was as low as 6.16 μΩ·cm. These findings demonstrate the positive effect of LM on Cu-Cu joints and offer a novel theoretical foundation for improving the electrical and mechanical properties of such joints.

Small-Signal Impedance and Split C-V Characterization of High-κ SiC Power MOSFETs

In this work, the improvement of SiC power MOSFET performance achieved using high-κ gate-dielectrics instead of the standard SiO2 is investigated by means of advanced gate-impedance characterization. The benefit of using high-κ gate-dielectrics with high dielectric constant is demonstrated by comparing SiC MOSFETs with pure high-κ, a stack of SiO2/high-κ, as well as pure SiO2. Namely, the fabricated high-κ SiC MOSFETs show a superior performance to commercial SiC MOSFETs with SiO2/SiC interface with respect to channel resistance and interface quality. The proposed characterization approach is non-destructive and applicable to packaged power devices.

Rapid formation, grain refinement and shear property of high-temperature-stable full IMC joints

Solid liquid interdiffusion (SLID) bonding that can fabricate high-melting point full IMC joints is playing an increasing key role in 3rd-generation semiconductor power electronic device packaging for high temperature applications. In this study, rapid formation of Cu/intermetallic compounds (IMCs)/Cu–8Ni joints with fine (Cu,Ni)6Sn5 and (Cu,Ni)3Sn grains was achieved by SLID bonding Cu/Sn/Cu–8Ni structure. The formation and evolution of the IMCs and the elemental distribution and shear property of the full IMC joints during bonding and subsequent aging were systematically investigated. Due to the Ni doping, the growth of the (Cu,Ni)6Sn5 IMC was significantly accelerated during bonding while that of the Cu3Sn phase was strongly suppressed during both bonding and aging. The total IMC growth rate in the Cu/Sn/Cu–8Ni solder joints was approximately 44 times faster than that in the Cu/Sn/Cu solder joints under the same bonding condition. After aging at 260 °C for up to 400 h, the full IMC joints showed good thermostability composing of fine IMC grains and no Kirkendall voids were observed. The shear strength of the full IMC joints slightly dropped from 63.17 MPa after bonding to 54.35 MPa after aging. The proposed SLID bonding using Cu/Sn/Cu–8Ni structure was proved to be a promising method for forming high-temperature-stable full IMC joints for 3rd-generation semiconductor power device packaging or 3D packaging applications.

Low-Temperature Transient Liquid Phase Bonding Technology via Cu Porous-Sn58Bi Solid–Liquid System under Formic Acid Atmosphere

This study proposes a low-temperature transient liquid phase bonding (TLPB) method using Sn58Bi/porous Cu/Sn58Bi to enable efficient power-device packaging at high temperatures. The bonding mechanism is attributed to the rapid reaction between porous Cu and Sn58Bi solder, leading to the formation of intermetallic compounds with high melting point at low temperatures. The present paper investigates the effects of bonding atmosphere, bonding time, and external pressure on the shear strength of metal joints. Under formic acid (FA) atmosphere, Cu6Sn5 forms at the porous Cu foil/Sn58Bi interface, and some of it transforms into Cu3Sn. External pressure significantly reduces the micropores and thickness of the joint interconnection layer, resulting in a ductile fracture failure mode. The metal joint obtained under a pressure of 10 MPa at 250 °C for 5 min exhibits outstanding bonding mechanical performance with a shear strength of 62.2 MPa.

Kinetics of Cu6Sn5 and Cu3Sn intermetallic compounds growth and isothermal solidification during Cu-Sn transient liquid phase sintering process

The kinetics of Cu-Sn intermetallic compounds (IMCs) growth relates to the materials preparation, process regulation and reliability prediction in the new energy field and electronic packaging industry. As a typical instance that Cu-Sn IMCs are involved with, this work investigated the kinetics of Cu-Sn IMCs growth and isothermal solidification of Cu-Sn transient liquid phase sintering (TLPS) process for high temperature resistant packaging of the third-generation semiconductors power devices. A three-dimensional kinetics model of Cu/Sn solid/liquid interfacial reaction and the corresponding kinetics equations of Cu6Sn5 and Cu3Sn growth was established. Based on Cu-Sn IMCs growth kinetics, a parameter ξSn called the residual rate of Sn was defined to characterize the isothermal solidification kinetics of Cu-Sn TLPS process. By measuring the volume fraction of Cu and Sn, the quality fraction of residual Cu and Sn and produced Cu-Sn IMCs were determined, and thus the kinetics of Cu-Sn IMCs growth and the isothermal solidification of Cu-Sn TLPS process were experimentally studied to validate the theoretical model. The results showed that the theoretical results predicted by the model were well-matched with experimental results. Besides rising temperature, the kinetics of Cu-Sn IMCs growth and the isothermal solidification can be remarkably accelerated by decreasing Cu particle size. Reducing Sn content does not affect the kinetics of Cu-Sn IMCs growth but helps to shorten the isothermal solidification time of Cu-Sn TLPS process.

Sintering of mixed Cu[sbnd]Ag nanoparticles pretreated by formic acid vapor for Cu[sbnd]Cu low temperature bonding

In this work, a CuCu low temperature bonding method by using mixed CuAg nanoparticles (NPs) paste was proposed. To remove the oxide on the surface of Cu NPs, formic acid vapor pretreatment process was applied to treat the mixed CuAg NPs paste at 180 °C for 30 min. After the 30-min pretreatment, the oxide on Cu NPs was effectively reduced and the bonding quality has significantly improved. A reliable CuCu bonding was successfully achieved at the temperature of 250 °C for 30 min under a low pressure of 5 MPa after the pretreatment of formic acid vapor and the average shear strength achieved approximately 60.5 MPa. For mixed CuAg NPs paste sintering at 250 °C, the average resistivity reached 39.7 μΩ·cm after the pretreatment. Besides, with the bonding temperature increasing, especially after the pretreatments of formic acid vapor, the bonding interfaces became more compact and the fracture surfaces exhibited more distinct ductile deformations, which further illustrates the high quality of bonding. According to the results, this bonding technology is promising to be widely used in power device packaging.

Ceramic Additive Manufacturing Potential for Power Electronics Packaging

Compared with silicon-based power devices, wide bandgap (WBG) semiconductor devices operate at significantly higher power densities required in applications, such as electric vehicles and more electric airplanes. This necessitates the development of power electronics packages with enhanced thermal characteristics that fulfill the electrical insulation requirements. The present research investigates the feasibility of using ceramic additive manufacturing (AM), also known as three-dimensional (3-D) printing, to address thermal and electrical requirements in packaging gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs). The goal is to exploit design freedom and manufacturing flexibility provided by ceramic AM to fabricate power device packages with a lower junction-to-ambient thermal resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\theta \text {JA}}$ </tex-math></inline-formula> ). Ceramic AM also enables incorporation of intricate 3-D features into the package structure in order to control the isolation distance between the package source and drain contact pads. Moreover, AM allows to fabricate different parts of the packaging assembly as a single structure to avoid high thermal resistance interfaces. For example, the ceramic package and the ceramic heatsink can be printed as a single part without any bonding layer. Thermal simulations under different thermal loading and cooling conditions show the improvement of thermal performance of the package fabricated by ceramic AM. If assisted by an efficient cooling strategy, the proposed package has the potential to reduce <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\theta \text {JA}}$ </tex-math></inline-formula> by up to 48%. The results of the preliminary efforts to fabricate the ceramic package by AM are presented, and the challenges that have to be overcome for further development of this manufacturing method are recognized and discussed.

Die-attach bonding at 230 °C using micron Sn-coated Zn particles for high-temperature applications

The advancement of wide bandgap semiconductors has posed higher requirements for power chip packaging technology. Nanoparticles (Ag, Cu, and Cu@Ag) sintering was regarded as an innovative low-temperature bonding method that can be serviced at a high temperature. Considering the expensive cost of silver nanoparticles, Zn particles have been considered as an alternative. Herein, a novel type of submicron Sn-coated Zn particles was proposed to overcome the easy oxidation and high sintering temperature problem of Zn. The structure of Zn70Sn30 (wt.%) core/shell was determined by Scheil model calculation to meet the requirements of low-temperature bonding and high-temperature applications. Multiple reducing agents and reduction times were tentatively investigated to prepare Zn70Sn30 (wt.%) particles. The solder joints prepared based on Zn@Sn preform achieved bonding at 230 °C and exhibited an average shear strength of 28.13 MPa at 250 °C. Unlike the Zn–30Sn solder alloy, the lower reflow temperature produced only a single layer of Cu5Zn8 at the interface of the solder joint, which ensured that all fractures occurred primarily in the Zn@Sn preforms. The electrical resistivity and thermal expansion coefficients of Zn@Sn preform were 8.1 μΩ cm and 12.7 × 10−6/K, respectively. Therefore, the Zn@Sn particles were a potential die-attach material for high-temperature power device packaging.