Thermal management has always played a significant role in power module design. Double-sided heat dissipation is more efficient at transferring heat than the traditional package. Although there are several thermal modeling approaches to power modules, the application of the numerical models, which are computationally fast and accurate, has rarely been investigated for double-sided heat dissipation scenarios. This paper proposes a numerical heat conduction model of a double-sided heat dissipation power module with multiple chips embedded. The model was developed by solving Laplace’s equation for the temperature distribution of steady state heat transfer using the separated variable method. The individual chip placement, two-chip distance and orientation, and four-chip placement were discussed through this modeling approach. The optimal layout was found. Then, a half-bridge topology module that consisted of two chips was investigated. To verify the accuracy of the numerical model, Finite Element Analysis (FEA) of the model was performed using the same boundary conditions. The experiments were applied on the power cycling tester to extract the junction temperature and case temperature. The numerical methods show good temperature prediction accuracy compared to both FEA and experiments.@en

The nano-copper particles are widely used in the sintering processes of packaging wide bandgap semiconductors. Despite the significant success in the industry, the mechanism bridging the sintering process to the mechanical properties of sintered nano-copper is not yet well-modeled. In this paper, the impacts of different sintering temperatures and initial porosities caused by different stacking patterns on the uniaxial tensile performance of the sintered layer were studied via a molecular dynamics approach. Two stacking patterns, simple cubic and face-centered cubic, were simulated, respectively. Evolution of their structure at temperatures of 300, 400, 500, and 600 K were simulated as the sintering process. Afterward, the sintered structures were subjected to uniaxial tensile with rates of 0.01 and 0.04 Å/ps at different temperatures to compare the mechanical properties. The results show that the sintering rate and density of the sintered structure increase with a higher temperature. However, the tensile strength of the sintered structure is less relevant to the difference in stacking pattern. This study proves that porosity has a greater effect on sintering quality.@en

During operation in environments containing hydrogen sulfide (H₂S), such as in offshore and coastal environments, sintered nanoCu in power electronics is susceptible to degradation caused by corrosion. In this study, experimental and molecular dynamics (MD) simulation analyses were conducted to investigate the evolution and mechanism of H₂S-induced corrosion of sintered nanoCu, and bulk Cu was used as the reference. The following results are obtained: (1) Both sintered nanoCu and bulk Cu reacted with O₂ prior to reacting with H₂S, forming Cu₂O, Cu₂S, CuO, and CuS. In addition, sintered nanoCu exhibited more severe corrosion. (2) For both sintered nanoCu and bulk Cu, H₂S-induced corrosion resulted in the deterioration of electrical, thermal, and mechanical properties, and sintered nanoCu experienced a greater extent of deterioration. (3) As was ascertained through Reactive Force Field (ReaxFF) MD simulations, the penetration of H₂S and O₂ combined with the upward migration of Cu resulted in the formation of a corrosion film. In addition, compared to bulk Cu, the H₂S and O₂ penetration in the sintered nanoCu structure was observed to occur to a greater depth, accounting for the more pronounced performance degradation.

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The (Ca, Sr) AlSiN₃:Eu²⁺(CSASN:Eu) red phosphor is widely used to improve color rendering of high-power phosphor-converted lighting diode (pc-WLED), but it is always unstable under high temperature and high humidity environments. Therefore, the studies on the temperature and humidity resistance of red phosphors and their aging mechanism have become essential to evaluate its reliability in harsh applications. In this paper, the pressure cooker test (PCT) and 85°C&85% RH aging test were carried out for the CSASN:Eu red phosphors. And, its hydrolysis reaction-driven degradation mechanism was simulated and analyzed based on first-principle calculation, in which the optimized adsorption of simplified CaAlSiN3(CASN) and H2 O was simulated based on Density Function Theory (DFT) and the specific aging process was analyzed by the charge density difference and ab initio molecular dynamics (AIMD). The experimental results showed that the photoluminescence performance of CSASN:Eu red phosphor dropped gradually and finally disappeared under PCT aging, and its temperature-dependent degradation kinetics followed the Arrhenius model well. Meanwhile, the simulation results indicate that the CASN, reacted with H2 O when the H atoms had a tendency to approach N atoms. Both the temperature and humidity could accelerate the hydrolysis reaction rate.@en

This paper investigates thermomigration (TM) and electromigration (EM) in SWEAT structure. Firstly, the distribution of temperature along SWEAT structure during EM is obtained by using finite element (FE) simulation. The FE simulation results show that the temperature is almost uniformly distributed in the most region of narrow line in SWEAT structure, but temperature decreases rapidly at both sides of conductor. Accordingly, the temperature gradient in the narrow line of SWEAT structures is calculated. Then, we apply the obtained temperature and temperature gradient in the governing equation of EM in terms of atomic concentration. The numerical results show that the TM caused by temperature gradient causes the material depletion near both ends of conductor. At the same time, atoms diffuse from the middle region of conductor to both sides driven by the atomic concentration, causing the voids in middle of conductor.@en

Nano-metal materials sintering has received increasing attention in recent years for its promising performance in the wide bandgap semiconductor packaging. In this paper, molecular dynamics (MD) simulation method were applied to simulate the nano-Cu sintering mechanism and the subsequent mechanical behavior. Hybrid sintering, comprising nanosphere (NS) and nanoflake (NF), was carried out at temperatures ranging from 500K to 650K. Furthermore, shearing simulations were conducted with constant strain rates on the sintered structure at multiple temperatures, and subsequently correlated the extracted mechanical properties with the sintering behavior. The results indicated that the mechanical properties of nano-Cu sintered structure were 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 41.2GPa and 3.51GPa respectively. It offers valuable insights into the preparation phase of nano Cu paste for sintering technology.@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.

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Sintered nano-silver die-attach materials have been widely used in high-power electronics packaging because of their high thermal and electrical conductivities. In this study, we characterized the tensile properties of sintered nano-silver particles over a range of strain rates and temperatures, and established the constitutive models. First, 50 nm nano-silver particles were sintered at 275 °C for 50 min as test samples, and their tensile tests were conducted under a dynamic thermomechanical analyzer (DMA Q800) and an IBTC 300SL in-situ mechanical test system respectively with different strain rates and ambient temperatures. Then, both Anand and variable-order fractional models (VoFM) were adopted to analyze the obtained stress-strain data and we studied their fitting accuracy and applicability. The results showed that: (1) The Young's modulus of the sintered nano-silver particles decreased with increasing temperature. In addition, the tensile strengths declined under lower strain rates and higher temperature conditions; (2) both the Anand model and VoFM characterized the tensile stress-strain properties of the sintered nano-silver material well. Compared to the Anand model, the VoFM utilized a simpler formula with fewer parameters and higher precision.@en

As a core packaging material of light color conversion, phosphor/silicone composite plays an indispensable role in light emitting diode (LED) packaging. At present, commercial LED packages mainly use blue LED chips to stimulate Yttrium Aluminum Garnet (YAG) yellow phosphor to reach a white color. However, (Ca,Sr)AlSiN 3 :Eu 2+ (CSASN) red phosphor is often added to improve the color-rendering performance given the absence of red light emission spectrum. However, inevitably harsh working conditions can induce the degradation of CSASN red phosphor, which will directly influence the mechanical properties of its silicone composites and challenge the reliability of its LED packaging. In this study, the coupling effects of temperature–humidity–sulfur on the mechanical degradation of CSASN phosphor/silicone composites were considered. The prepared CSASN phosphor/silicone test samples were first aged under high-temperature, high-humidity, and high-sulfur conditions. A series of dynamic mechanical analysis tests were then conducted to qualitatively evaluate their mechanical properties. Finally, the dynamic tension process and interfacial cracking of CSASN phosphor/silicone composites were simulated by using finite element analysis with cohesive modeling. The results showed that: (1) under coupled aging conditions, the mechanical properties of the phosphor/silicone composite decreased due to the reaction of phosphor with sulfur, water, and oxygen; (2) crack initiation and propagation were most likely to occur at the edge of the crack perpendicular to the tensile direction. The debonding of particles with silicone rather than the fracture of phosphors was one of the main aspects resulting in failure mechanisms; (3) the highly concentrated and localized phosphor in the silicone matrix and the irregular shape and arrangement of phosphor particles generated cracks in the phosphor/silicone composite.@en

A fan-out panel-level packaging (FOPLP) with an embedded redistribution layer (RDL) via interconnection reduces the size, thermal resistance, and parasitic inductance of power module packaging. In this study, the effect of the RDL via size on the reliability of a FOPLP SiC MOSFET power module was investigated. To improve the thermal management and thermal cycling reliability of the designed SiC module, genetic algorithm (GA)–assisted optimization methods were proposed to optimize the RDL via size. First, the heat dissipation and the plastic work density of the SiC MOSFET module with various via diameters and depths were simulated using finite element simulations. Next, both the ant colony optimization-backpropagation neural network (ACOBPNN) with finite element simulation and the nondominated sorting genetic algorithm (NSGA-II) with theoretical model were developed to optimize the RDL via size. The results revealed that: (1) smaller via depth and size reduce the heat dissipation and thermal cycling reliability of the RDL via; (2) through both the ACO-BPNN and NSGA-II, the same optimal heat dissipation and plastic work density can be achieved in the designed module. (3) ACO-BPNN with assist of finite element simulation can provide a more effective optimization in complex packaging structure.@en

The increased system complexity in electronic products brings challenges in a system level reliability assessment and lifetime estimation. Traditionally, the graph model-based reliability block diagrams (RBD) and fault tree analysis (FTA) have been used to assess the reliability of products and systems. However, these methods are based on deterministic relationships between components that introduce prediction inaccuracy. To fill the gap, a Bayesian Network (BN) method is introduced that considers the intricacies of the high-power light-emitting diode (LED) lamp system and the functional interaction among components for reliability assessment and lifetime prediction. An accelerated degradation test was conducted to analyze the evolution of the degradation and failure of components that influence the system level lifetime and performance of LED lamps. The Gamma process and Weibull distribution are used for component level lifetime prediction. The junction tree algorithm was deployed in the BN structure to estimate the joint probability distributions of the lifetime states. The degradation and prediction results showed that LED modules contribute a major part for lumen degradation of LED lamps followed by drivers and the least effect is from diffuser and reflector. The BN based lifetime estimation results also exhibited an accurate prediction as validated with the Gamma process and such improved reliability assessment outcomes are beneficial to LED manufacturers and customers. Thus, the proposed approach is effective to evaluate and address the long-term reliability assessment concerns of high-reliability LED lamps and fulfill the guarantee of high prediction accuracy in less time and cost-effective manner.

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With their advantages of high efficiency, long lifetime, compact size and being free of mercury, ultraviolet light-emitting diodes (UV LEDs) are widely applied in disinfection and purification, photolithography, curing and biomedical devices. However, it is challenging to assess the reliability of UV LEDs based on the traditional life test or even the accelerated life test. In this paper, radiation power degradation modeling is proposed to estimate the lifetime of UV LEDs under both constant stress and step stress degradation tests. Stochastic data-driven predictions with both Gamma process and Wiener process methods are implemented, and the degradation mechanisms occurring under different aging conditions are also analyzed. The results show that, compared to least squares regression in the IESNA TM-21 industry standard recommended by the Illuminating Engineering Society of North America (IESNA), the proposed stochastic data-driven methods can predict the lifetime with high accuracy and narrow confidence intervals, which confirms that they provide more reliable information than the IESNA TM-21 standard with greater robustness.

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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.

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In this paper, large-scale molecular dynamic (MD) simulation is performed to investigate the concentration-dependent vacancy volume relaxation in Al, Cu, and Au, respectively. The vacancy volume relaxation factor is calculated and correlated to the microstructure change based on MD results. It is found that the vacancy volume relaxation factor is nearly a constant at low to mid-vacancy concentration level, i.e., from 10−6 to 10−3 of the lattice concentrations. However, the volume of vacancies will completely collapse at the high vacancy concentration, and the coalescence of vacancies will form massive dislocations. The simulation results are in good agreement with the existing data from both experiments and simulations in the literature. A uniform empirical equation is developed to obtain the vacancy volume relaxation factor as a function of vacancy concentration. Furthermore, the hydrostatic stress is also calculated based on MD simulations. This paper also discusses the relationship between the vacancy volume relaxation and the diffusion-induced strain, such as in the application of electromigration. For a constrained condition, the hydrostatic stresses obtained from MD-based vacancy volume relaxation and a commonly used stress-vacancy equation are compared. An insight on the critical vacancy concentration at which electromigration failure would occur is discussed in detail.@en

To meet the requirements of low temperature packaging and high temperature operation for wide bandgap semiconductors, the traditional reflow soldering is gradually substituted by the metallic nanoparticle sintering interconnection. However, the high sintering densification is one of necessities to achieve the high reliable packaging. To reveal the mechanism of nano-copper particles sintering interconnection, this paper firstly establishes the relationship between the particle size ratio and the stacking porosity through the three-dimensional (3D) non-isodiametric double sphere stacking modeling. Then, the Monte Carlo simulation is performed to investigate the sintering process of nano-copper particles with different size ratios. Finally, a sintering experiment with the mixture of two types of nano-copper particles is used to validate the proposed models and simulations. The results show that, according to three 3D stacking models, the stacking porosity is lowest when the particle size ratio is between 10:1 and 5:1. Through the Monte Carlo simulation, the model with a particle size ratio of 5:1 has the largest sintering shrinkage. The experiment by mixing the 250 nm and 50 nm nano-copper particle shows the highest relative density of sintered samples when the particle mass ratio is 8:1, which is consistent with the theoretical calculations. Thus, the proposed method in this study can provide theoretical supports to the nano-copper sintering interconnection application and process optimization in the wide bandgap semiconductor packaging.

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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.

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Solder joint fatigue is one of the critical failure modes in ball-grid array packaging. Because the reliability test is time-consuming and geometrical/material nonlinearities are required for the physics-driven model, the AI-assisted simulation framework is developed to establish the risk estimation capability against the design and process parameters. Due to the time-dependent and nonlinear characteristics of the solder joint fatigue failure, this research follows the AI-assisted simulation framework and builds the non-sequential artificial neural network (ANN) and sequential recurrent neural network (RNN) architectures. Both are investigated to understand their capability of abstracting the time-dependent solder joint fatigue knowledge from the dataset. Moreover, this research applies the genetic algorithm (GA) optimization to decrease the influence of the initial guessings, including the weightings and bias of the neural network architectures. In this research, two GA optimizers are developed, including the “back-to-original” and “progressing” ones. Moreover, we apply the principal component analysis (PCA) to the GA optimization results to obtain the PCA gene. The prediction error of all neural network models is within 0.15% under GA optimized PCA gene. There is no clear statistical evidence that RNN is better than ANN in the wafer level chip-scaled packaging (WLCSP) solder joint reliability risk estimation when the GA optimizer is applied to minimize the impact of the initial AI model. Hence, a stable optimization with a broad design domain can be realized by an ANN model with a faster training speed than RNN, even though solder fatigue is a time-dependent mechanical behavior.

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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.

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At present, most high-power white Light-emitting diode and laser diode (LED&LD) package is usually constructed by a blue LED&LD chip with a Cerium doped Yttrium Aluminum Garnet (YAG:Ce³⁺) yellow phosphor, but its color rendering performance is severely challenged due to the lack of red light emission spectrum. The CaAlSiN₃:Eu²⁺ red phosphor can effectively improve the color quality of traditional yellow phosphor converted white LED&LDs(pc-wLED&LDs), however, it is often susceptible to degradation under high temperature and high humidity environments, which will directly affect the color quality of pc-wLED&LDs. In this study, a series of water immersion tests on CaAlSiN₃:Eu²⁺ red phosphor are used to quantitatively study its hydrolysis reaction kinetics. Then, the degradations of its photoluminescence and photothermal performances are evaluated by characterizing the crystal structure, micromorphology and chemical element composition. Finally, an atomic level hydrolysis reaction mechanism of CaAlSiN₃:Eu²⁺ red phosphor is investigated by using the first-principles density functional theory (DFT) calculation. The results show that: (1) By modelling the in-situ monitored electrical conductivity of CaAlSiN₃:Eu²⁺ red phosphor water solution with a first-order reaction function, the calculated hydrolysis reaction rate satisfies the Arrhenius relationship and the reaction activation energy is estimated as 49.19 kJ/mol; (2) The increased self-heating effect of CaAlSiN₃:Eu²⁺ red phosphor after water immersion test attribute to its drastic drop of light emission efficiency; (3) The hydrolysis reaction mechanism of CaAlSiN₃:Eu²⁺ red phosphor is confirmed, which sequentially results in the dissolution of Ca²⁺ and OH⁻, the crash of host lattice and the accumulation of reaction residues.

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In this paper, a recently developed theory - general coupling model of electromigration, is implemented in ANSYS. We first identify several errors provided in ANSYS manual for electromigration modeling. Then the general coupling model is implemented in ANSYS and the detailed description is presented. Finally, a 1-D confined metal line with a perfectly blocking condition is presented as a benchmark problem, in which the finite element solutions are in excellent agreement with the analytical solutions.

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