Average Junction Temperature Research Articles

Maximizing liquid-cooled heat sink efficiency with advanced topology-optimized fin designs

Direct-to-chip liquid cooling offers significant advantages in managing higher power densities compared to traditional air-cooling methods. This approach utilizes nearly half the power required by server fans and air conditioners, enhances cooling efficiency in data centers. The effectiveness of this cooling strategy is intricately linked to the layout of the cold plate fins. In this research, a density-based topology optimization method is implemented in generating free-forming and non-intuitive fin structures. A pseudo-optimization model, which approximates the 3D heat sink as two 2D thermally coupled problem is selected and optimized with ‘pressure drop’ and ‘average junction temperature’ as objective function and constraint, respectively. Several fin layouts with inlet flow velocities and temperature constraints are generated. Three-dimensional numerical simulations reveal that the average junction temperature with the topology-optimized fin pattern is ∼2°C higher, and the pressure drop is significantly lower compared to size-optimized straight channel. Building on this, an inverted topology-optimized design is introduced along the channel length, inspired by the wavy nature of sectional fins. The average junction temperature with the inverted TO design is 3 to 4°C lower compared to the straight design, with a similar pumping power of 0.023 W. The TO fin layout capitalizes on frequent re-initialization of boundary layers, secondary flow-induced mixing, and the formation of Dean vortices along the channel length. Further refinement leads to the derivation of drop-oblique-trapezoidal and oval-shaped (DOTO) fins. These fins reduce average junction and wall temperatures by ∼23% compared to the inverted TO design, owing to the persistent effects of fluid dynamic phenomena along the channel length. Comparison with benchmarked designs indicates that DOTO fins reduce the average junction temperature by 3 to 6°C compared to size-optimized offset strip fins and step fins, with a similar pumping power of 0.083 W. The study indicates that optimizing DOTO fins dimensions can further enhance heat sink performance.

Performance of power dissipation on semiconductor module for different configuration of heat SINK with thermal pad

An experimental and numerical investigation to assess the impact of the number of fin arrangements on heat dissipation and its subsequent influence on junction temperature under natural convection. The experimental phase incorporated a thermal pad with a thermal conductivity of 12 W/mK and an aluminum heat spreader measuring (17x16.5) mm. By utilizing the finite volume method (FVM), a numerical model was developed that closely resembles the experimental setup, with errors for temperature package and heat spreader measured at 0.08% and 4.49%, respectively. The analysis was carried out for five different numbers of fins, specifically s1=4fins, s2=6fins, s3=8fins, s4=10fins and s5=12fins. According to the numerical analysis, the increase in the number of fins from 4 to 12 led to a reduction in the average junction temperature from 79.11 °C to 75.97 °C. This denotes a decrease of 3.97% in the average junction temperature. The inclusion of fins on the heat spreader brought about an upsurge in conduction resistance from 55.77 °C/W to 56.19 °C/W, while the convective resistance observed a decline from 152.35 °C/W to 139.62 °C/W. By increasing the number of fins from 4 to 12, the Nusselt number experiences a monotonic decrease from 14.44 to 14.141 due to the reduction in fin-to-fin spacing. As a result, this would lead to a decrease in the natural convection flow. Hence, it was concluded that increasing number of fins beyond the optimal number of fins, signifying the point where thermal benefits become insignificant. The results of this study yield significant insights into the optimization and design of thermal solutions for semiconductor modules, ultimately providing a pathway to boost their operational efficiency and longevity in real-world applications.

Performance enhancement of topology-optimized liquid-cooled heat sink with increased spanwise length of design domain

Topology optimization generate promising ‘heat sink fin layouts’ to satisfy the thermo-hydraulic objectives with lightweight designs. This article evaluates the performance of topology-optimized liquid-cooled heat sinks with different spanwise length-based design domains. A reduced-scale model (with 1/8th the width of the full-scale heat sink model) is selected and optimized with ‘pressure drop’ and ‘average junction temperature’ as objective functions and constraints, respectively. Fin layouts consisting of non-continuous fins are derived for different inlet flow velocities and temperature constraints using an accurate two-dimensional (2D) mathematical model, mimicking a three-dimensional (3D) heat sink geometry. Three-dimensional CFD simulation is used to compare the performance of the present fin layout with a reference topology-optimized design (with 1/16th the width of the full-scale model) and an augmented straight channel-based heat sink. To cool the heat sink to an average junction temperature of 50 °C, the present design requires 17 % and 54 % lower pumping power compared to the reference design and straight channel with significantly reduced material volume. Flow phenomena such as secondary flow-induced mixing and frequent reinitialization of boundary layers at leading edges of fins are observed during numerical investigation which are illustrated using velocity and temperature contours. The optimized fin layout's overall performance is compared with existing fin designs of heat sinks such as step fins, offset strip fins, oblique fins, and oblique and trapezoidal fins. Oblique and trapezoidal fin and oblique fin compete with topology optimized design which outperforms at lower flow rates (for velocity ranging from 0.05 m/s to 0.175 m/s). The average junction temperature using Oblique and trapezoidal fins and oblique fins are 63 °C and 61.22 °C, respectively compared to 58.5 °C for topology-optimized design with a similar pressure drop of 300 Pa.

Influence of substrate size and gas on thermal and optical performance of LED filament bulbs

LED filament lamp with high brightness, low power consumption and long life, is a new generation of LED lighting new light source. Although the high-density integration of LED chips into the substrate can provide more functionality, but the LED filament heat dissipation performance aspects is a major problem affecting the luminous efficiency and reliability. Here, the LED chips were solid-crystallized onto 1.5 mm and 3.0 mm ceramic substrates, and the effects of substrate size and filling gas on the heat dissipation and optical performance of the filament lamps were investigated by finite element analysis (FEA). The heat distribution, luminous flux and luminous efficiency of the bulb surface were analyzed. The simulation results show that filling helium has better heat dissipation and optical performance than filling nitrogen or air, and the average junction temperature of the LED filament decreases from 119.28 °C to 105.40 °C, the luminous flux increases from 551.66 lm to 583.38 lm, and the luminous efficacy increases from 142.5 lm/W to 151.1 lm/W when the substrate size is changed from 1.5 mm to 3.0 mm. It can be seen that increasing the size of the substrate, LED filament lamp heat dissipation effect and optical performance is better. Experimental tests also support the simulation results. The results provide guidance for the thermal design of high-power LED filament bulbs.

The effects of input power and ambient temperature on the thermal performance of conical pin fin heat sink in natural convection

In the present study, thermal performance tests of horizontally oriented HSconical, HScross-cut, and HSflat with a base plate dimensions of 80*80*5 mm3 were performed in natural convection. The effects of ambient temperature (30 and 40 °C), input power (16.5 and 33 W), and conical pin fin geometry on the thermal performance of the HSs were investigated. The thermal resistance of the heat sinks decreases while the convective heat transfer coefficient, average surface temperature, and average junction temperature increase with increasing ambient temperature and input power. However, the Nusselt number increases with increasing ambient temperature for all HSs at 16.5 W, while the Nusselt number decreases with increasing ambient temperature at 33 W. The highest convective heat transfer coefficients are 32.17, 30.68, and 19.61 W/m2K for HSconical, HSflat, and HScross-cut at 33 W and 40 °C, respectively. The lowest thermal resistances are 2.75, 2.80, and 3.81 K/W for HSconical, HScross-cut, and HSflat at 33 W and 40 °C, respectively. Thermal resistances of HSconical and HScross-cut decreased by 27.78 % and 26.44 % at maximum and 27.06 % and 24.58 at minimum, respectively, compared to HSflat. The results show that the conical fins have better thermal performance in natural convection.

Simple Hybrid Model for Estimating Remaining Useful Life of SiC MOSFETs in Power Cycling Experiments

Recording and prediction of the accumulated damage, which will eventually lead to the failure of power electronic modules, is an aspect of high importance for power electronic systems design and, in particular, for development of Prognostic and Health Management (PHM) schemes for in-field applications. To this end, this paper presents a simple and cost-effective prognostic method for predicting the remaining useful life (RUL) of TO-247 packaged silicon carbide (SiC) metal-oxide semiconductor field-effect transistors (MOSFETs) subjected to power cycling experiments. The model assumes that the major failure mode is bond-wire lift-off and uses a damage accumulation scheme based on Paris’ crack law. The only inputs to the model are historical data on the average junction temperature swing and the temperature-compensated drain-source ON-state resistance at the peak temperature of the current cycle. Using only these two input values, the model is shown to predict RUL with surprising accuracy for the range of constant current loads determining cycling conditions under which the test data series have been acquired. This work is a first step in an ongoing project towards building more elaborate prognostic schemes for RUL-determination of SiC power MOSFETs in actual working conditions, using physics-informed neural networks (PINNs).

Data-driven voltage/var optimization control for active distribution network considering PV inverter reliability

Fully exploiting the reactive power support capability of the distributed photovoltaic power supply is helpful to solve the problems of voltage fluctuation, voltage overlimit and new energy consumption in the distribution network. However, the reactive power output of the photovoltaic power supply will seriously threaten the reliable operation of the photovoltaic inverter. Therefore, this paper proposes a data-driven voltage-reactive optimization control strategy considering the reliability of the photovoltaic inverter. Firstly, the data-driven model is used to calculate the insulated gate bipolar transistor junction temperature, which improves the calculation efficiency of the insulated gate bipolar transistor junction temperature and reduces the dependence of the evaluation accuracy on the insulated gate bipolar transistor parameters. Then, the voltage-reactive optimization control model of the distribution network considering the reliability of the photovoltaic inverter is established, and the average junction temperature and junction temperature fluctuation of the insulated gate bipolar transistor are introduced into the model optimization goal. The optimization model is transformed into the reinforcement learning task, and then the deep deterministic policy gradient algorithm is used to realize voltage-reactive control. According to the simulation of IEEE 33 node distribution system, the proposed strategy can increase the minimum and average insulated gate bipolar transistor lifetime of all nodes by 6 years and 4 years. At the same time, it can reduce the minimum and average levelized cost of energy of all nodes by 0.1095 $/W and 0.0318 $/W.

Multidimensional Mission-Profile-Based Lifetime Estimation Approach for IGBT Modules in MMC–HVdc Application Considering Bidirectional Power Transfer

MMC applied in high voltage direct current (HVdc) field consists of numerous submodules (SMs) and supports bidirectional power transfer, leading to the diverse mission and temperature profiles among SMs and IGBT modules. In this paper, an IGBT lifetime estimation approach in terms of the bidirectional power transfer of MMC is proposed. The temperature profile of each module is translated based on the multi-dimensional mission profile, including arm current, heatsink temperature, active power, and reactive power. In this way, the average junction temperature and junction temperature fluctuation of each SM can be readily estimated according to the power transfer direction. Furthermore, both the line-frequency and low-frequency fatigue are considered in the estimation process by using corresponding lifetime models. The proposed lifetime estimation method is compared with the traditional power loss average method and one-direction power transfer method by the application of the multi-dimensional mission profile of the practical Nanao project. The results show the bidirectional power transfer has a big influence on the damage distribution inside SM. The lower IGBT, upper FWD, and lower FWD all suffer considerable degradation under bidirectional power transfer conditions. Moreover, bond wire fatigue is the dominant degradation mechanism in MMC-HVdc application.

Real-Time Average Junction Temperature Estimation for Multichip IGBT Modules With Low Computational Cost

The junction temperature of the insulated gate bipolar transistor (IGBT) modules is a vital parameter for the reliability of the power electronic system. For effective thermal management, it is necessary to estimate junction temperature in real time. However, existing thermal models have limitations to achieve fast temperature prediction for multichip IGBT modules. In this study, we investigate the real-time junction temperature prediction for multichip IGBT modules with low computational cost. According to the power module' structure, an average 2D thermal model with physical significance is proposed to predict the virtual junction temperature for multichip IGBT modules, which can be extracted from finite element model based on the least square method. To further improve the computational efficiency, a temperature predictor based on the staggered cycle-by-cycle calculation method is proposed and its prediction error under various extreme operation conditions is analyzed by enumeration method. Finally, the comprehensive experimental results verify the effectiveness of the proposed average thermal model and junction temperature prediction method.

Comparative Study of the Parameter Acquisition Methods for the Cauer Thermal Network Model of an IGBT Module

Under the operating conditions of high power and high switching frequency, an insulated gate bipolar transistor (IGBT) chip can produce relatively large power loss, causing the junction temperature to rise rapidly; consequently, the reliability of the IGBT module can be seriously affected. Therefore, it is necessary to accurately predict the junction temperature of the IGBT chip. The resistance capacitance (RC) thermal network model is a commonly used method for IGBT junction temperature prediction. In this paper, the model parameters are obtained by two methods to establish the Cauer thermal network models of the IGBT module. The first method is to experimentally obtain the transient thermal impedance curve of the IGBT module and the structure function and then extract the individual thermal parameters of the Cauer thermal network model; the second method is to obtain the thermal parameters of the thermal network model directly by using theoretical formulas that consider the influence of the heat spreading angle. The predicted junction temperatures of the Cauer thermal network models established by the two methods are compared with the junction temperatures obtained from infrared (IR) measurements during the power cycling test, the junction temperatures measured by the temperature-sensitive electrical parameter (TSEP) method, and the junction temperatures calculated by finite element (FE) analysis. Additionally, the Cauer thermal network models established by the two methods are compared and verified. The results indicate that the Cauer thermal network model established based on theoretical formulas can accurately predict the maximum junction temperature of the IGBT chip, and the calculated temperature for each layer, from the IGBT chip layer to the ceramic layer, also accords well with the FE results. The Cauer thermal network model established based on the experimental test and the structure function can accurately predict the average junction temperature of the IGBT chip.

Power Cycling Test를 통한 4H-SiC MOSFETs의 계면 열화 분석

In this paper, we performed a power cycling test (PCT) under harsh operating conditions, such as an average junction temperature (TSUBjm/SUB) of 120°C and a junction temperature gradient (ΔTSUBj/SUB) of 110°C to analyze the degradation characteristics of commercial 4H-SiC MOSFETs. For accurate analysis, various electrical characteristics such as output curve, transfer curve, gate leakage current curve, and voltage-capacitance curve were measured before and after PCT and were compared. In addition, transmission electron microscopy (TEM) and simulation were utilized. Both voltage-capacitance curves and TEM images after PCT show degradation of the SiO₂/SiC interface.

Module Lifetime Evaluation Method for the Power Converter of the DFIG Based on the Analysis of the Field Wind Speed Probability and Ambient Temperature

The junction temperature fluctuation (ΔTj) of the doubly fed induction generator (DFIG) around the synchronous speed point, deteriorates the reliability of the power converter considerably. Therefore, a lifetime evaluation method for the power converter of DFIG is proposed in this paper. Combining the speed-power curve of the generator with the grid side converter (GSC) and the rotor side converter (RSC), and using the equivalent thermo-electric network of IGBT module, the junction temperature (Tj) model of the power converter is established to calculate the average junction temperature and fundamental frequency temperature fluctuation. Based on the field measured data of the wind speed probability and ambient temperature of three wind power plants in different latitude region, the operation life curves of GSC and RSC are obtained by curve fitting, and the life spans of five type of power modules are evaluated and compared. It can be seen that the lifetime of the converter could be reduced significantly due to the ambient temperature-induced low frequency temperature fluctuations in the thermal cycling, while, the fundamental frequency thermal cycle caused by the running frequency of the converter has slight effect on the overall life.

Effect of different soldering temperatures on the properties of COB light source

PurposeThe purpose of this paper is to investigate the effect of different soldering temperatures on the performance of chip-on-board (COB) light sources during vacuum reflow soldering.Design/methodology/approachFirst, the influence of the void ratio of the COB light source on the steady-state voltage, luminous flux, luminous efficiency and junction temperature has been explored at soldering temperatures of 250°C, 260°C, 270°C, 280°C and 290°C. The COB chip has also been tested for practical application and aging.FindingsThe results show that when the soldering temperature is 270°C, the void ratio of the soldering layer is only 5.1%, the junction temperature of the chip is only 76.52°C, and the luminous flux and luminous efficiency are the highest, and it has been observed that the luminous efficiency and average junction temperature of the chip are 107 lm/W and 72.3°C, respectively, which meets the requirements of street lights. After aging for 1,080 h, the light attenuation is 84.64% of the initial value, which indicates that it has higher reliability and longer life.Originality/valueIt can provide reference data for readers and people in this field and can be directly applied to practical engineering.

Thermofluidic characteristic of a nanofluid-cooled oblique fin heat sink: An experimental and numerical investigation

This paper presents an experimental and numerical investigation on the thermofluidic performance of 0.5–2.0 % of the volumetric concentration of Al2O3-water nanofluids through oblique fin heat sink microchannel (OFHS MC) in the Reynolds number range 100–300. In comparison, experiments were also performed using a straight channel heat sink microchannel (SCHS MC) of the same hydraulic diameter as the oblique fin channel. The fluid flow is simulated using the RNG k-ε model in both periodic and full domain numerical analysis. The phenomenological behaviour of the nanofluid flow is further studied using numerical results. The oblique fin microchannel encouraged the secondary flow, thus enhanced the macroscopic mixing. Boundary layer disruption and vortices generation in the secondary channel is the critical phenomena of improved heat transfer. A substantial improvement of heat transfer coefficient is achieved for nanofluid and oblique fin heat sink combinations compared to the straight channel heat sink. The heat transfer coefficient is increased at increasing nanofluid concentrations for any given Reynolds number and channel configuration. The enhancement of about 55 % in the heat transfer coefficient with a 2 % volumetric concentration of nanofluid is achieved at Re = 300 in an oblique fin heat sink. The heat transfer enhancement is always significant than the pressure penalty. The oblique fin heat sink improves the average junction temperature considerably compared to the straight channel heat sink. The inclusion of nanofluid can reduce the experimental junction temperature by up to 6 °C. Therefore, the combined advantage of the oblique fin heat sink with nanofluid is anticipated as one of the potential alternatives for electronics cooling.

Stochastic Finite Element Thermal Analysis of a Ball Grid Array Package

Abstract This paper presents a straight-forward finite element approach for the quantification of electronic package thermal performance under uncertainty. The method makes use of high accuracy sensitivity calculations and a gradient-based minimization method. The approach was applied to the thermal analysis of a ball grid array (BGA) package under uncertainty to illustrate its capabilities. The effect of uncertainty in the heat source, heat transfer coefficient, ambient temperature, and thermal conductivities of the component materials on the probability of exceeding a specified average junction temperature at the die-heat-spreader interface was studied. In addition, the performance and accuracy of two different methods for computing the required sensitivities were compared. Results showed that the average junction temperature probability was more sensitive to some system parameters over others, providing crucial information for selecting the manufacturing tolerance of BGA package components. For parameters identified as especially sensitive, selecting components with tighter tolerances will reduce uncertainty and increase the overall reliability. And for less sensitive parameters, selecting larger tolerance could help reduce manufacturing costs.

Transient junction temperature prediction of IEGT in modular multilevel converter sub-module based on FEM

Compared with plastic module IGBTs, press-pack IEGTs (PPI) can carry higher current due to the special package design with double-side cooling and the elimination of bonding wire, and are perfect devices for VSC-HVDC converter. The reliability of VSC-HVDC is closely related to the junction temperature of PPI devices, so it is extremely important to accurately predict the junction temperature of PPI. The traditional junction temperature prediction method, basing on RC-lumped network, is employed widely to estimate the average junction temperature. However, it’s difficult to demonstrate the details of each chip when considering the thermal coupling of IEGT chip. Therefore, a prediction method of junction temperature considering thermal coupling is proposed to calculate the transient junction temperature of PPI in the modular multilevel converter (MMC). By calculating the current of the MMC sub-module, the PPI loss model is established in ANSYS/TwinBuilder. Besides, the thermal network of PPI with the heatsink is established by CFD. Furthermore, the transient junction temperature of PPIs is calculated with the 1500MW MMC system. The results show that the proposed prediction method can not only predict the transient junction temperature of PPI modules in MMC sub-module, but also obtain the details of thermal distribution.

On the Lifetime Estimation of SiC Power MOSFETs for Motor Drive Applications

This work presents a step-by-step procedure to estimate the lifetime of discrete SiC power MOSFETs equipping three-phase inverters of electric drives. The stress of each power device when it is subjected to thermal jumps from a few degrees up to about 80 °C was analyzed, starting from the computation of the average power losses and the commitment of the electric drive. A customizable mission profile was considered where, by accounting the working conditions of the drive, the corresponding average power losses and junction temperatures of the SiC MOSFETs composing the inverter can be computed. The tool exploits the Coffin–Manson theory, rainflow counting, and Miner’s rule for the lifetime estimation of the semiconductor power devices. Different operating scenarios were investigated, underlying their impact on the lifetime of SiC MOSFETs devices. The lifetime estimation procedure was realized with the main goal of keeping limited computational efforts, while providing an effective evaluation of the thermal effects. The method enables us to set up any generic mission profile from the electric drive model. This gives us the possibility to compare several operating scenario of the drive and predict the worse operating conditions for power devices. Finally, although the lifetime estimation tool was applied to SiC power MOSFET devices for a general-purpose application, it can be extended to any type of power switch technology.

Optimum Composition of Vacuum Content in a Spiral-Like Flexible Chimney-Based LED Bulb1

This paper introduced the gas flow and optimization of a spiral-like flexible chimneybased LED bulb by a combined mathematical and experimental study. A mathematical model of spiral flexible LED bulb considering nature convection, radiation and heat transfer was established by the FLOEFD software based on the finite element method (FEM), and was also compared with the experimental result. The effect of chimney-self based and vacuum content on the thermal performance of a bulb was studied. A thermal resistance model was proposed for analytical model. Compared with the filament with a stretch height of 3cm, the chimney effect can reduce the average junction temperature of filament by 6.38 ℃ (through the experiment) and 6.48 ℃ (through the simulation) respectively. The results revealed that the chimney effect has a huge impact on the gas flow in the bulb. The cause of the phenomenon is that flexible LED filament can improve the gas flow by changing self-shape instead of other cooling device. A vacuum content was introduced in the bulb and composition was optimized by using analytical model. The filament temperature in optimized bulb could decrease 6 0C than full filled with helium.

Research on on-line monitoring technology of IGBT module junction temperature based on Kalman filter

IGBT is the core device of energy conversion and transmission, commonly known as the CPU of power electronic devices. However, with the continuous improvement of IGBT power density, its reliability is increasingly concerned by industry and academia. The failure of IGBT module is mainly related to the average junction temperature and the amplitude of junction temperature fluctuation, and with the increase of the amplitude of junction temperature fluctuation, the number of failure cycles of IGBT module will sharply decrease. It can be seen that the change of junction temperature in power module is the key to affect its fatigue life. In this paper, an on-line junction temperature monitoring method based on Kalman filter is proposed, which combines the actual temperature measured by IGBT module with the junction temperature obtained by RC thermal network, so it has the advantages of high reliability and real-time on-line monitoring. The simulation results show the effectiveness of the method.

Liquid cooling module incorporating a metal foam and fin hybrid structure for high power insulated gate bipolar transistors (IGBTs)

We propose a liquid cooling system incorporating a porous medium combined to the multiscale flow manifold. Specifically, this work compares two types of porous media by varying the porosity: the first type only includes a metal foam layer, and the second incorporates an additional circular pin-fin array within the metal foam. The thermohydraulic performances of each type such as the average junction temperature, temperature deviation, flow were investigated using both numerical and experimental approaches. Due to the influence of the additional thermal conductivity matrix by fin structure integration, the second configuration (metal-foam and pin-fin hybrid type) provides a higher thermal performance compared to the first one. The suggested cooling solution with the second configuration could provide a very low thermal resistance (~0.185 K/W) with the pressure drop range between 5 and 15 kPa, which surpasses the performances of the previous-reported direct liquid cooling solutions such as the jet impingement, turbulator, and microchannel. This work will help develop high performance and compact cooling solutions for high power semiconductor applications such as an insulated gate bipolar transistor (IGBT) or a microprocessor.