Understanding the atomic diffusion features in metallic material is significant to explain the diffusion-controlled physical processes. In this paper, using electromigration experiments and molecular dynamic (MD) simulations, we investigate the effects of grain size and temperature on the self-diffusion of polycrystalline aluminium (Al). The mass transport due to electromigration are accelerated by increasing temperature and decreasing grain size. Magnitudes of effective diffusivity (Deff) and grain boundary diffusivity (DGBs) are experimentally determined, in which theDeffchanges as a function of grain size and temperature, butDGBsis independent of the grain size, only affected by the temperature. Moreover, MD simulations of atomic diffusion in polycrystalline Al demonstrate those observations from experiments. Based on MD results, the Arrhenius equation ofDGBsand empirical formula of the thickness of grain boundaries at various temperatures are obtained. In total,DeffandDGBsobtained in the present study agree with literature results, and a comprehensive result of diffusivities related to the grain size is presented.@en

In high power electronics packaging, sintered silver nanoparticle joints suffer from thermal-humidity- electrical-chemical joint driven corrosion in extreme environments. In this paper, we conducted aging tests on sintered silver nanoparticles under high-temperature, high-humidity, and high-sulphur conditions. The results show that: (1) the sample under the dry high-sulphur conditions at a high temperature exhibited the highest degree of sulphidation; (2) Reactive force field (ReaxFF) molecular dynamics (MD) simulations of sintered silver nanoparticle sulphidation revealed the sulphidation layer was formed by silver atoms upward migration. This work paves the way for further investigation on sintered silver nanoparticles corrosion considering multi-physics coupling effects.@en

YAG: Ce3+ phosphor/silicone composites are widely used in solid-state lighting as a light converter to achieve white lighting. However, because of high thermal resistance and low thermal stability, the luminous performance of YAG: Ce3+ phosphor/silicone composite deteriorates rapidly when excited by high-power-density blue-laser. To explore the potential of blue laser-excited YAG: Ce3+ phosphor/silicone composites, the luminous performances under different blue laser power conditions were characterized by both the reflective and transmissive excitations using a self-built three-integrating-sphere system. Furthermore, the Monte-Carlo Ray-tracing simulation was used to illustrate the light-transmission and energy conversion mechanism in the phosphor/silicone composites. The results showed that: (1) The YAG: Ce3+ phosphor/silicone composite could be excited by the 0.292W laser light with the peak wavelength of 445nm, excessive laser power will cause phosphor thermal quenching and silicone carbonization. (2) The luminous flux of the composite under both the reflective and transmissive excitations gradually increased with the increase of phosphor concentration; correspondingly, the color coordinate moved to the yellow region, and the Correlated Color Temperature (CCT) gradually decreased. (3) The simulation results indicated that under the same phosphor concentration, the luminous flux obtained by reflection excitation was largely higher than that by the transmission excitation, as the light re-conversion and strong back-scattering were occurred in the reflective and transmissive laser excitation respectively.@en

In a light-emitting diode (LED) package, silicone encapsulant serves as a chip protector and enables the light to transmit, since it exhibits the advantages of high light transmittance, high refractive index, and high thermal stability. However, its reliability is still challenged under harsh operation conditions. In this study, the optical and mechanical properties of silicone encapsulant, including appearance, light transmittance, Young’s modulus, and tensile strength, were experimentally monitored during the sulfur-rich ageing process. Meanwhile, the Fourier transform infrared (FTIR) spectroscopy and molecular dynamics (MD) simulation were used to reveal its degradation mechanism. The results show that 1) in the sulfur (S8)-rich ageing process, the severe vulcanization reaction occurred in silicone encapsulant assisted only by high temperature and high moisture, with the existence of H2S as the reaction product of S8 and H2O vapor. 2) Vulcanization characterized by the formation of the sulfhydryl (-SH) group lowered both optical and mechanical properties of silicone encapsulant. 3) The hydrolysis reaction featured by the formation of the hydroxyl (-OH) group decreased the mechanical performances of silicone encapsulant but brought slight harm to its optical performances.@en

This paper presented integrated electromigration (EM) studies through experiment, theory, and simulation. First, extensive EM tests were performed using Blech and standard wafer-level electromigration acceleration test (SWEAT)-like structures, which were fabricated on four-inch wafers. Second, a molecular dynamics (MD) simulation-based diffusion-induced strain was incorporated into the existing coupled theory. Third, one-dimensional (1D) governing equations in terms of atomic concentration for un-passivated and passivated configurations were derived for void formation and growth, using a modified Eshelby's solution to consider the effect of passivation. Fourth, a systematic approach was established, including theoretical formulations and experimental methods, to obtain key material properties, i.e., critical atomic concentration and diffusivity. We then determined the material's properties from a specific set of experimental data, using aluminium (Al) as a carrier for demonstration. These properties were then used to predict the time to failure and void growth under various conditions. The theoretical results agreed well with the experimental data. Moreover, we theoretically determined the critical threshold products of current density and conductor length for the un-passivated and passivated configurations, respectively. Both experiment and theory showed that, in the absence of mechanical stress in un-passivated configurations, the atomic self-diffusion, which was opposite to electron wind, was significant in resisting EM development. However, when mechanical stress was present, such as in passivated configurations, stress migration played a dominant role in resisting EM development. Our numerical results showed that the current density exponent n in Black's law remained as 2 in the range of the current density greater than 0.2 MA/cm2 and rapidly approached infinity at a low level of current density.@en

This paper presented a comprehensive experimental and simulation study for thermomigration (TM) accompanying electromigration (EM) at elevated current densities. Both Blech and standard wafer-level electromigration acceleration test (SWEAT)-like test structures, with aluminum (Al) as a carrier, were used for testing and analysis. In Part I of our study (Cui et al., 2023a), the experimental and numerical results with the current density of 1 MA/cm2 were presented. We observed that Al stripes with a SWEAT structure did not show damage in the entire length, while Blech structures showed void and hillock formations only at the cathode and anode, respectively. The temperature gradient owing to Joule heating was neglected in our previous simulations, and the predicted results agreed well with the experimental observations. However, we have not theoretically verified the effect of the temperature gradient. In this paper, we first reported the new experimental data under the elevated current densities of 3 and 5 MA/cm2. In both Blech and SWEAT structures, the spreading of voids in the middle region of conductors was observed. Moreover, in Blech structures, voiding in the middle region occurred after a period of time when voids/hillocks were formed at the cathode and anode, while the SWEAT structures did not show damage at the two ends. Next, based on the coupled 3D theory (Cui et al., 2023a), new analytical one-dimensional (1D) solutions were derived for the Blech and SWEAT structures in the un-passivated configuration considering TM. We found that TM played a significant role in the EM development in the middle of conductors under the elevated current density. The numerical results were in excellent agreement with the experimental data with the consideration of TM. We further established new EM failure's threshold criteria for the SWEAT structures in the form of the product of current density and square of conductor length. This is a major departure from the original Blech's theory in which only mechanical stress gradient was considered. We also studied the acceleration factor of the current density exponent and presented an insight into failure mechanisms associated with TM.@en

As a promising technology for high-power and high-temperature power electronics packaging, nanocopper (nanoCu) paste sintering has recently received increasing attention as a die-attachment. The high-temperature deformation of sintered nanoCu paste and its underlying mechanisms challenge the reliability of high-power electronics packaging. In this study, the tensile deformation behaviors of sintered nanoCu paste were firstly characterized by high-temperature tensile tests performed at various temperatures and strain rates ranging from 180 °C to 360 °C, 1 × 10−4 s−1 to 1 × 10−3 s−1 respectively. It was found that the elastic modulus and tensile strength decreased at the higher tensile temperature while the ductility increased accordingly. The highest elastic modulus and tensile strength results were 12.15 GPa and 46.97 MPa, respectively. Second, failure analysis was conducted based on the fracture surface after tensile testing. Recrystallization was revealed as the main factor for ductility improvement. Subsequently, an Anand model was fitted by stress-strain curves to describe the tensile constitutive behavior of the sintered nanoCu paste. Multi-scale modelling techniques also investigated the impact of tensile temperature and strain rate on the tensile response. Molecular dynamics simulation was implemented using a hemispherical Cu nanoparticle model to reveal the properties from an atomistic perspective. In addition, a two-dimensional equivalent model was further established by using a stochastically distributed void morphology. The multi-scale modelling techniques successfully describe the evolution of tensile response to the different tensile temperatures and strain rates. Besides, the equivalent model with random void morphology was demonstrated as the finite element simulation results were highly consistent with the high-temperature tensile experiments.@en

A molecular dynamics (MD) simulation was performed on the coalescence kinetics and mechanical behavior of the pressure-assisted Cu nanoparticles (NPs) sintering at low temperature. To investigate the effects of sintering pressure and temperature on the coalescence of the nanoparticles, sintering simulations of two halve Cu NPs were conducted at the pressure of 0–300 MPa and the temperature of 300–500 K. A transition of the dominant coalescence kinetics from slight surface diffusion to intensive grain boundary diffusion and dislocation driven plastic flows were found when pressure was applied. Furthermore, atomic trajectories showed the effect of temperature on sintering was strongly dependent on the microstructures of Cu NPs. The atomic diffusion around defects can be significantly promoted by the elevated temperature. Additionally, based on the sintered structures, uniaxial tension simulation was implemented with a constant strain rate. Stress–strain curves and evolution of dislocation activities were derived. Improved mechanical behaviors, including larger elastic modulus and larger tensile strength, were obtained in the structure sintered under higher pressure and temperature. Among this study, sintering temperature and pressure consistently exhibited the same relative impact on affecting both coalescence and the mechanical properties of the sintered structure.@en

MAlSiN3:Eu2+ (M = Ca, Sr) is commonly used in high-power phosphor-converted white-light-emitting diodes and laser diodes to promote their color-rendering index. However, the wide application of this phosphor is limited by the degradation of its luminescent properties in high-temperature, high-humidity, and high-sulfur-content environment. Here, the degradation mechanism of the (Sr,Ca)AlSiN3:Eu2+ (SCASN) red phosphor under thermal-moisture-sulfur coupling conditions is investigated. Furthermore, by performing first-principles calculations, the hydrolysis mechanism on an atomic scale is assessed. The adsorption energy (Eads) and charge transfer (ΔQ) results showed that H2O chemically adsorbed on the (0 1 0), (3 1 0), and (0 0 1) surfaces of the CaAlSiN3 (CASN) host lattice. The energy barrier for H2O dissociation is only 29.73 kJ mol−1 on the CASN (0 1 0) surface, indicating a high dissociation probability. The formation of NH3, Ca(OH)2, and CaAl2Si2O8 is confirmed by H+ tended to combine with surface N atoms, while OH− combined with the surface Al/Si or Ca atoms. Moreover, ab initio molecular dynamics simulations were performed to further understand the hydrolysis process. This work offers a guidance on the design and applications of luminescent materials in LED packages with higher reliability and stability requirements in harsh environment.@en

The CaAlSiN3:Eu2+ red phosphor and its silicone/phosphor composite are very promising materials used in the high color rendering white light-emitting diode (LED) packaging. However, the reliabilities of CaAlSiN3:Eu2+ and its composite are still being challenged by phosphor hydrolysis at high humidity application condition. A fundamental understanding of the interface adhesion between silicone and CaAlSiN3:Eu2+ is significant for the developments and applications of this material. In this work, the mechanical properties of silicone/pristine CaAlSiN3:Eu2+ and silicone/hydrolyzed CaAlSiN3:Eu2+ composites are experimentally measured and compared firstly, in which both the tensile strength and Young's modulus of composite are increased after the hydrolysis reaction. Then, the first principles Density Functional Theory (DFT) calculations are used to investigate the adhesion behaviors of the silicone molecular on both the pristine and the hydrolyzed CaAlSiN3[0 1 0] at atomic level. The results show that: (1) The silicone molecular is weakly adsorbed on the pristine CaAlSiN3[0 1 0] via Van der Waals (vdW) interactions, while silicone molecular is much stronger absorbed on the hydrolyzed CaAlSiN3[0 1 0] due to the formation of hydrogen bonding at the interface; (2) The transient state calculations indicate that the sliding energy barrier of silicone on the hydrolyzed CaAlSiN3[0 1 0] is higher than that on the pristine one, as the increased adsorption energy and surface roughness. Generally, the findings in this paper can guide the phosphor selection, storage and process in LED packaging, and also assist in improving the reliability design of LED package used in high moisture condition.@en

Owing to its low cost and high efficiency, the blue light-emitting diode (LED) chip covered with the Y3Al5O12:Ce3+ (YAG) phosphor has become a mainstream technology of high power white LED packaging. However, phosphors are often susceptible to degradation under high-temperature and high-humidity conditions, which directly affects the optical and color stability of the white LED package. In this study, the moisture resistance of YAG phosphor was evaluated through both a short-term water-immersion test and long-term aging tests, i.e. 85 °C&85% Relative Humidity (RH) test and high-temperature and saturated humidity test. The phosphor hydrolysis mechanism was then revealed by characterizing the phosphor emission spectrum, photothermal property, crystal structure, micromorphology, and chemical element composition.@en

The power semiconductor joining technology through sintering of copper nanoparticles is well-suited for die attachment in wide bandgap (WBG) semiconductors, offering high electrical, thermal, and mechanical performances. However, sintered nanocopper will be prone to degradation resulting from corrosion in sulfur-containing corrosive environments such as offshore areas. In this study, experiments, including aging test and corrosion characterization, and simulations based on density functional theory (DFT) studies were conducted to explore the corrosion behavior and mechanism of elemental sulfur (S8) and hydrogen sulfide (H2S) on sintered nanocopper. The experimental results indicated that loose corrosion products were observed on the sintered nanocopper during the ageing process involving S8, and compact layered corrosion products formed during the ageing process involving H2S. Furthermore, similar corrosion product compositions (Cu2O, Cu2S, CuO, CuS, and potentially Cu2SO4 or CuSO4) were observed in both the S8- and H2S-ageing processes. However, the S8-ageing process exhibited more noticeable corrosion penetration. This was explained in simulations results: the unsaturated Cu sites on the oxide layer [Cu2O(1 1 1)] of the sintered nanocopper could adsorb both H2S and S8, while the saturated Cu sites only exhibited the potential to adsorb S8.@en

The power semiconductor joining technology through sintering of copper nanoparticles is well-suited for die attachment in wide bandgap (WBG) semiconductors, offering high electrical, thermal, and mechanical performances. However, sintered nanocopper will be prone to degradation resulting from corrosion in sulfur-containing corrosive environments such as offshore areas. In this study, experiments, including aging test and corrosion characterization, and simulations based on density functional theory (DFT) studies were conducted to explore the corrosion behavior and mechanism of elemental sulfur (S8) and hydrogen sulfide (H2S) on sintered nanocopper. The experimental results indicated that loose corrosion products were observed on the sintered nanocopper during the ageing process involving S8, and compact layered corrosion products formed during the ageing process involving H2S. Furthermore, similar corrosion product compositions (Cu2O, Cu2S, CuO, CuS, and potentially Cu2SO4 or CuSO4) were observed in both the S8- and H2S-ageing processes. However, the S8-ageing process exhibited more noticeable corrosion penetration. This was explained in simulations results: the unsaturated Cu sites on the oxide layer [Cu2O(1 1 1)] of the sintered nanocopper could adsorb both H2S and S8, while the saturated Cu sites only exhibited the potential to adsorb S8.@en

The power semiconductor joining technology through sintering of copper nanoparticles is well-suited for die attachment in wide bandgap (WBG) semiconductors, offering high electrical, thermal, and mechanical performances. However, sintered nanocopper will be prone to degradation resulting from corrosion in sulfur-containing corrosive environments such as offshore areas. In this study, experiments, including aging test and corrosion characterization, and simulations based on density functional theory (DFT) studies were conducted to explore the corrosion behavior and mechanism of elemental sulfur (S8) and hydrogen sulfide (H2S) on sintered nanocopper. The experimental results indicated that loose corrosion products were observed on the sintered nanocopper during the ageing process involving S8, and compact layered corrosion products formed during the ageing process involving H2S. Furthermore, similar corrosion product compositions (Cu2O, Cu2S, CuO, CuS, and potentially Cu2SO4 or CuSO4) were observed in both the S8- and H2S-ageing processes. However, the S8-ageing process exhibited more noticeable corrosion penetration. This was explained in simulations results: the unsaturated Cu sites on the oxide layer [Cu2O(1 1 1)] of the sintered nanocopper could adsorb both H2S and S8, while the saturated Cu sites only exhibited the potential to adsorb S8.@en

In high-power electronics packaging, nano-silver sintering technology has been widely applied due to its excellent electrical and thermal conductivity and its low-temperature packaging and high-temperature operation. In this study, 50-nm nano-silver particles are sintered at 275°C for 50 min and placed under a dynamic thermomechanical analyzer (DMA Q800) with three strain rates (0.001%s-1, 0.01%s-1, and 0.1%s-1) and seven ambient temperatures (-40°C, 0°C, 25°C, 60°C, 120°C, 150°C, and 185°C). Both the variable-order fractional constitutive model and Anand model are adopted to characterize the tensile behaviors of sintered nano-silver particles. The results show that (1) the tensile strength of sintered nano-silver particle samples declines under the lower strain rate and higher temperature; and (2) both the variable-order fractional model and Anand model can well represent the tensile mechanical properties of sintered nano-silver. According to the root mean square error (RMSE) calculation, the fitting accuracy of the variable-order fractional model is slightly better than that of the Anand model. Furthermore, the variable-order fractional model involves fewer parameters, which makes it easier to fit than the Anand model. @en

High-power white light-emitting diodes (LEDs) have demonstrated superior efficiency and reliability compared to traditional white light sources. However, ensuring maximum performance for a prolonged lifetime use presents a significant challenge for manufacturers and end users, especially in safety–critical applications. Thus, identifying functional anomalies and predicting the remaining useful lifetime (RUL) is of enormous importance in the operational longevity of the device. To address such challenges, this study proposes a combination of distance-based Mahalanobis distance (MD), entropy generation rate (EGR), and deep learning models for improved anomaly detection and RUL prediction accuracy. Unlike conventional health indicators based on luminous flux data that are challenging to monitor relevant optical performance, the MD and EGR methods are employed to extract in-situ monitored thermal and electrical data as new health indicators. Long short-term memory recurrent neural networks (LSTM-RNN) and convolutional neural networks (CNN) are established to detect anomalies and predict the RUL. The accelerated degradation tests of 3 W high-power white LED have been conducted, and the online and offline collected experimental data are deployed for model development and performance evaluation. The performance of the proposed methods is compared against the Illuminating Engineering Society of North America (IESNA) TM-21 method. The results indicate that LSTM-RNN, when combined with either MD or EGR, can detect anomalies with significantly fewer data (70 %) than is typically required. Furthermore, a significant improvement in prediction accuracy in RUL prediction based on MD and EGR-constructed time series health indicators and employed with the LSTM-RNN model demonstrates the effectiveness of the proposed methods.@en

Nano-metal materials have received considerable attention because of their promising performance in wide bandgap semiconductor packaging. In this study, molecular dynamics (MD) simulation was performed to simulate the nano-Cu sintering mechanism and the subsequent mechanical behaviors. Hybrid sintering, comprising nanosphere (NS) and nanoflake (NF), was performed at temperatures from 500 to 650 K. Furthermore, shear and tensile simulations were conducted with constant strain rates on the sintered structure at multiple temperatures. Subsequently, the extracted mechanical properties were correlated with the sintering behavior. The results revealed that the mechanical properties of the nano-Cu sintered structure could be improved by tuning material composition and increasing the sintering temperature. We established a relationship between the sintered microstructure and mechanical response. The shear modulus and shear strength of the sintered structure with NF particles increased to 41.20 and 3.51 GPa respectively. Furthermore, the elastic modulus increased to 55.60, and the tensile strength increased to 4.88 GPa. This result provides insights into the preparation phase of nano-Cu paste for sintering technology.@en

Driving by the increased demand for hermetic packaging in the more than Moore (MtM) roadmap, a Cu nanoparticle sintering-enabled hermetic sealing solution was developed with a small-size sealing ring. The developed technology simplifies microfabrication and requires less surface roughness using a sinterable Cu nanoparticle paste. A 50μm size Cu paste sealing ring was achieved using a lithography patterned photoresist as a stencil mask. A groove-structured chip was used to amplify localized stress. The Cu nanoparticle paste was fully sintered at 300 °C under pressure ranging from 10 to 40 MPa resulting in a robust bonding with a maximum shear strength of 280 MPa and implementing hermetic packaging. The deflection of the Si diaphragms estimated a vacuum level of 7 kPa. Vacuum sealing was maintained for over six months, and the lowest leak rate was calculated as 8.4× 10 -13Pa·m 3/s. The developed technology that comprises small-size patterning and pressure-assisted sintering offers the potential for a simple, cost-effective, but robust solution for hermetic packaging.@en

As a critical part of speeding up industrial electrification, power electronics, and its packaging technology are undergoing rapid development. Cu nanoparticle sintering technology has therefore received extensive attention for its excellent performance in the die-attachment layer, where the mechanical properties are essential to be known for design for reliability. Both sintering and subsequent nanoindentation were studied by simulation. The effect of porosity on the nanoindentation response was investigated by setting different initial packing densities. In addition, the impact of indenter size and indentation positions on the nanoindentation response were discussed. The nanoindentation behaviors were studied by extracting loading-displacement (P-h) curves and calculating elastic modulus and hardness. In addition, the microstructure evolution was adopted using atomic configuration to study the nanoindentation mechanism. This work offers valuable insights into the Cu sinter paste preparation phase for sintering technology.@en

Some atrial contractile assist devices applied on the heart surface can be regarded as a laminated Liquid crystal elastomer (LCE) plate under steady temperature loads and a contact mechanical force. An exact solution for the deformation of the laminated LCE plate under combined thermal and mechanical loads is derived by solving the three-dimensional (3D) equilibrium equations including heat conduction and thermoelastic theory. The validity of mathematical formula and computer programming is proved by convergence and comparison examples with finite element method (FEM). In order to simplify the complex calculation of exact solution, a back propagation neural network (BPNN) is further trained with a database containing 9504 sets of thermo-mechanical load conditions and their corresponding deformation which is solved by the exact solutions. Then the deformations of LCE plate subject to combined thermo-mechanical load can be predicted by this BP neural network instead of complex numerical calculation. Moreover, it is also applied to inverse the contact mechanical force at the bottom surface of LCE plate with a given deformation and temperature conditions. The results show that: (1) The results from the exact theoretical solution are in consistence with that from FEM but have a higher computational efficiency and stability; (2) The deformation of the laminated plate is more sensitive to the layered thickness of LCE than the variation of the temperature; (3) 3-D elasticity solutions of a laminated LCE plate under the combined thermos-mechanical load can be effectively predicted by a trained BP neural network.@en