Transient Thermal Measurements Research Articles

Exploring the process-microstructure-thermal properties relationship of resin-reinforced Ag sintering material for high-power applications via 3D FIB-SEM nanotomography

Resin-reinforced Ag sintering materials represent a promising solution for die-attach applications in high-power devices requiring enhanced reliability and heat dissipation. However, the presence of resin and intricate microstructure poses challenges to its thermal performance, and improvement strategies remain unclear. This work utilizes 3D FIB-SEM nanotomography to reconstruct the microstructure of this material under various process conditions. The analysis reveals that, even with an Ag volume fraction as low as 47.3%, Ag particles form a robust 3D network. Geometric tortuosity quantifies the effect of different sintering conditions on the Ag particle network in all spatial directions. Effective thermal conductivity is simulated based on realistic microstructure models. Results show a significant negative correlation between tortuosity and effective thermal conductivity. Increasing sintering temperature in Model B notably reduces tortuosity and enhances effective thermal conductivity. Sensitivity analysis underscores the dominant role of Ag volume fraction in regulating effective thermal conductivity. Finally, transient thermal impedance measurement of this material as a thin die-attach layer in actual high-power devices demonstrated its application potential. This article strives to explore the relationship between process, microstructure, and thermal properties of this material to provide a reference for further development.

Pressure-dependent thermal conductivity transient measurement of graphene

The thermal properties of graphene determine the thermal damage evaluation of graphene diaphragm and the lifetime of graphene-based devices. The conventional transient measurement method tends to result in the low-precision thermal conductivity (κ) for suspended monolayer graphene and complex interferometry setup. Hence, in order to improve κ measurement of graphene, a simple, miniaturized and portable Fabry-Perot (F–P) resonator with 10-layer graphene is proposed to perform the actuation and vibration detection of the suspended graphene. Then, the κ value can be calculated by means of laser-heated graphene's thermomechanical response, along with the established model for thermal time constant (τ) of a uniformly heated circular film. A quadratic fit is applied to the measured κ at different air pressures and an average fitting curve is obtained, thus determining that the measured κ relatively decreases by 13.32% with the increasing air pressure outside the F–P cavity from ∼22 kPa to ∼101 kPa. Subsequently, the COMSOL heat transfer simulation confirms that convective heat transfer is the primary reason for the external air pressure affecting transient measurements of κ of graphene. Hence, after taking the intercept of the average fitting curve, the predicted κ at 0 Pa of 10-layer suspended graphene is calculated to be 194.48 W/(m·K), which is close to the fitting curve calculated from previously reported κ of graphene with different layers. This study contributes to accurate transient measurement of κ in graphene, and is also instructive for investigating transient thermal process in other two-dimensional materials.

A novel heat transfer characterization method for a thermal management scheme of 3D-IC chips

A novel surface-modified silicon-based thermal management technology has been proposed for 3D IC architecture in this study. 2 × 2 cm2 double sides polished silicon chips’ surface with micro-fin (MF) and micro-pin fin (MPF) structures have been achieved by applying silicon microfabrication technology of deep reactive ion etching, which is applicable to the interlayer of 3D IC packaging technology. By integrating a mini wind tunnel with Raman spectrometer, the transient thermal property measurement system is originally designed to evaluate the cooling capability of the surface-modified silicon interlayer. Finite Element Analysis was involved to confirm this view by taking fluid dynamics and heat transfer into account. The sample with 100 × 100 µm2 MPF structure expresses the appropriate exponential decay time constant τ (with unit of 1), which is 4.71 and 8.53 under cooling and heating measurement conditions, respectively. This also proved that the combination of Raman thermometry with forced gas flow could be a relevant measurement tool for transient thermal property.

A new transient hot-wire thermal conductivity apparatus and measurements of helium at temperatures from 20 K to 300 K

In this study, an apparatus based on the transient hot-wire method (THW) was designed to measure the thermal conductivity of cryogenic fluid within the temperature range of 20–300 K and the pressure range of 0–20 MPa, with a relative expanded uncertainty Ur(λ) of 0.0284 (k = 2, 95 %). The experimental data of methane, ethane, and carbon dioxide showed good consistency with the ECS model, validating the reliability of the apparatus. In addition to the linear temperature dependence of hot-wire resistance above 70 K, the nonlinear temperature dependence below 70 K is calibrated, and the feasibility of the THW method for measurements in the temperature range of 20–70 K is validated. Subsequently, the thermal conductivity data for helium are presented from 20 to 300 K. The temperature rises of hot-wire during the measurement agreed well with the simulation calculation results. Furthermore, a thermal conductivity model for helium gas up to 600 K was developed. The presented data in this work, as well as previously published data, demonstrated good agreement with the model calculation results, with an average absolute relative deviation (AARD) of 1.46 %.

Electric Traction Motor Spray Cooling—Empirical Model Development and Experimental Validation

The growing interest in electric vehicles leads to new developments of efficient electric traction motors with high power density. Since a large part of the losses in an electric motor can occur in the windings, it is important to cool the windings to reduce the temperature and protect the winding insulation from thermal aging. Oil spray cooling systems are becoming more and more relevant for cooling the windings. In this work, an approach for heat transfer modeling of electric traction motors (power classes #2-4 with 60 to 180kW) with hairpin end windings is developed and tested. The model is developed with a testing rig for different flat jet spray nozzle arrangements for a hairpin electric traction motor. The model approach showed a good agreement with the measured temperatures of the end windings in the testing rig. A transient thermal simulation of the testing rig confirms the good agreement. In a second step the model approach is transferred to another electric traction motor with a different spray cooling system. The simulation results of the second electric traction motor also show good agreement with thermal quasi-static operating points and transient measurements at low and medium speed. At high speeds the deviations increased. Possible causes for this behavior are discussed.

Interaction Mechanism of Transonic Squealer Tip Cooling With the Effect of High-Speed Relative Casing Motion

Abstract The relative casing motion can significantly influence the turbine blade tip aerothermal performance. In this study, experimental investigation was conducted in a newly developed high-speed disk rotor rig which can mimic engine realistic high-speed casing relative motion while enabling full optical access to a transonic turbine blade tip surface. Spatially-resolved tip heat transfer data, including heat transfer coefficient and film cooling effectiveness, were obtained for a cooled transonic squealer tip by infrared transient thermal measurement. Combined with closely coupled Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) analysis, this paper reveals an interesting interaction mechanism between the cooling injections from the pressure side and the cavity floor with and without the effect of relative casing motion. Both experimental data and CFD results show a consistent trend in both heat transfer and cooling performance. With cavity cooling only, the cooling performance reduces with the effect of relative casing motion. However, with additional cooling injection from the pressure side, a significant improvement in the combined cooling performance with the relative casing motion can be observed. Such opposite trend highlights the importance of relative casing motion when ranking different tip cooling designs. With the consideration of relative casing motion, extra tip cooling benefit can be obtained by combining cooling injections from two different locations.

A numerical calibration of structure-function transient thermal measurement based on Cauer RC network

Structure functions were originally provided by V. Székely et al. as a nondestructive method for analyzing the thermal resistance of each layer. In this paper, we propose a numerical calibration of structure functions based on the Cauer RC network. The numerical calibration has practical physical significance and can be used as feedback to form a closed loop system in conjunction with the structure functions. A 3D finite element transient thermal simulation is analyzed by structure functions with different setting parameters to determine the feasibility of the numerical calibration. Furthermore, this numerical method can be used to obtain the transient thermal resistance of an ideal heat dissipation structure from the results of the transient dual interface measurement (TDIM).

Translation of outdoor tandem PV module I–V measurements to a STC power rating

AbstractThe procedures for the power rating of tandem‐cell‐based concentrator photovoltaic (CPV) modules defined in the international standard IEC 62670‐3 are adapted to the requirements of tandem‐cell‐based flat plate PV modules. The adjusted procedure describes how to translate outdoor measured PV current–voltage characteristics to standard test conditions (STC): 1000 W/m, 25°C cell temperature, AM1.5g spectral conditions. In this work, we describe how to obtain all required input parameters: thermal transient measurements to determine the module temperature coefficients, categorizing and filtering the prevailing spectral irradiance conditions using spectral matching ratios, and determining the 25°C module open‐circuit voltage from dark current–voltage curves. Three specimen PV modules (triple‐junction, III‐V on Silicon and III‐V on Germanium) have been measured for several months outdoors on a dual axis tracking unit at Fraunhofer ISE in Freiburg. In this work, we demonstrate that the CPV module power rating procedures in IEC 62670‐3 are also—in a modified form—to be recommended for the outdoor rating of tandem‐cell‐based flat plate PV modules.

Characterization and Optimization of the Heat Dissipation Capability of a Chip-On-Board Package Using Finite Element Methods

The present study endeavors to investigate the thermal dissipation capability of a chip-on-board package by means of a comprehensive experimental and numerical analysis. For this purpose, a BiCMOS chip is designed and fabricated in conjunction with three different printed circuit board configurations, including a single-sided board, a thermal via board, and a copper frame board. Transient thermal measurements are carried out on all three packages, and the results are subsequently transformed into cumulative structure functions. Then the finite element models are established for each package configuration, and their validity is confirmed through comparison with the experimental structure functions. The models are then characterized in accordance with the JEDEC 38-set boundary conditions, followed by a series of optimizations targeted towards the printed circuit board, including the board stack-up and the board sizes. Parametric studies are performed to quantitatively assess the impact of these parameters on the thermal performance. Finally, the present study provides a comprehensive discussion of the optimal application scenarios for each board configuration, with a view to achieving good thermal performance. The findings of this study will contribute to the development of more thermally effective chip-on-board packages for high-performance electronic systems.

A universal sensitivity matrix reduction technique (SMART) to uncover governing thermal transport relationships

Sensitivity analysis is a powerful technique to analyze the behaviors of models and experimental data. Most state-of-the-art characterization techniques rely on fitting experimental data to a theoretical multivariate model that can have multiple unknown properties other than the target property. Often, these unknowns cannot be measured separately and are unavoidably fitted for their values simultaneously using a single set of measured data. No rigorous method exists to evaluate their accuracy and elucidate the inherent governing relationships that can change with different measurement conditions. Here, we formulate a systematic approach based on sensitivity analysis to obtain these hidden relationships in a complex multivariate model. Criteria for simultaneously estimating the values of multiple unknowns are also clarified. We demonstrate this approach for a transient thermal transport measurement technique. This approach is versatile and can be applied to most measurement techniques in various disciplines that involve multivariate theoretical models to improve their measurement accuracy and throughput.

Out-of-plane transient thermal conductivity measurements for bulk semiconducting conjugated polymers using fast scanning calorimetry

The thermal conductivity for CP was enhanced with 5 wt% dopants but impaired with more than 20 wt% dopants. The enhanced thermal conductivity was attributed to higher rDOC and stronger π–π interactions due to small amount of active dopants.

Sensitivity of Adiabatic Cooling Effectiveness to Mainstream and Coolant Temperatures in Transonic Flow Over an Idealized Blade Tip Model

Abstract Film cooling, as a key technology to ensure turbine survival in new generation gas turbines, has been studied profusely in subsonic flows. But in transonic flow, the determination of adiabatic cooling effectiveness faces a dilemma in the state of the art. Specifically, derivation of reference temperature, or local recovery temperature, in adiabatic effectiveness is disputable. Some researchers designate it to be the adiabatic wall temperature for the uncooled model (linear regression method (LRM)), but others calculate it from an iterative procedure based on a pair of cooling tests (dual linear regression technique (DLRT)). As the first of the kind effort to explore this dilemma, this article carried out transient thermal measurements by infrared thermography, for transonic flow over an idealized blade tip model. Heat transfer experiments were conducted for the uncooled and cooled cases, at two mainstream temperatures of 340 K and 325 K and two coolant temperatures of 276 K and 287 K. Data from these six experimental groups were processed by LRM and DLRT, respectively, to obtain heat transfer coefficient and adiabatic effectiveness, whose sensitivity to mainstream and coolant temperatures is tested and compared. It is found that the heat transfer coefficient is basically insensitive to temperature boundary conditions and data reduction methods, as expected. However, for adiabatic effectiveness, LRM results are sensitive to the 11 K decrease of coolant temperature in areas confined to the upstream of cooling injection, and much less so to the 15 K rise in mainstream temperature. DLRT result, derived from the test pair with two coolant temperatures, reduces globally and conspicuously with 15 K increase in mainstream temperature. Furthermore, adiabatic effectiveness obtained by LRM is qualitatively different from that by DLRT, which is mainly attributed to the large discrepancy in reference temperature between the two methods.

Development of an optical thermography system using a pumped two-dye fluorescence technique

This work demonstrates the development of a novel backside thermography technique based on the temperature sensitivity of laser-induced fluorescence in flowing two-dye solutions. The approach utilizes visible light and optically transparent packaging materials to obtain spatially resolved transient thermal measurements. This makes it a relatively simple, inexpensive, and flexible approach for lab-scale experimental characterizations using economical cameras and optics. Additionally, both heating and cooling of the thermography stage can be achieved by passing temperature-controlled water through plastic packaging components. A custom-built experimental setup was designed, constructed, and used to study the performance of seven two-dye Rhodamine B (RhB)-Rhodamine 110 (Rh110) fluorescent solutions. The effect of dye concentration ratio on sensitivity, maximum frame rate, and excitation area was characterized. Using an optimal dye concentration of unity, it was shown that frame rates of 265–3200 Hz are achievable for excitation areas with diameters of 15.5–4.3 mm, respectively, using the current setup. The calibrated system was used to demonstrate in-situ measurements showing the importance of two-dye light compensation, as well as backside thermography using a simple droplet contact method to investigate temporal response. Experiments were conducted in the range of 25–55 °C with a spatial resolution of 30 µm. The experimental uncertainty of the temperature measurements was calculated to be ±2.1 °C and the technique's ability to account for error due to light fluctuations and non-uniform illumination was demonstrated. Finally, the effect of dye photobleaching during prolonged testing was studied and it was shown that photobleaching can be reduced, and even eliminated, by maintaining a nominal low flow rate of the pumped two-dye solution.

Analysis of the IGBT Module with Bonding Wire Failure Based on Transient Thermal Impedance

Insulated gate bipolar transistor(IGBT) modules are widely used in inverters as power switching devices. In actual working conditions, the failure of bonding wires is one of the most common failure modes. In the current device reliability evaluation, the influence of bonding wire failure is ignored, which may easily cause the subsequent evaluation results to deviate from the reality. In this paper, the influence of the gradual failure of the bonding wire on the transient thermal impedance of the device is explored, and the electro-thermal coupling model of the device is constructed. The simulation results show that the transient thermal impedance of the device increases with the gradual failure of the bonding wire. An experimental platform for transient thermal resistance measurement was built to verify the accuracy of the simulation results.

Thermographic network identification for transient thermal heat path analysis

ABSTRACT In this work, an evaluation method for transient thermal measurements is presented. It allows for a high temporal sensitivity by analysing the spectral composition of a thermal transient, the so-called time constant spectrum. The spectral components provide a detailed insight into the heat flow dynamics and thermal parameters describing a multi-layer system. The method is based on a one-dimensional heat path analysis technique common for the thermal characterisation of electronic components, called ‘network identification by deconvolution’. Here, a generalisation, called ‘thermographic network identification’, is presented to obtain spatially resolved thermal equivalence networks as complete thermal model of the device under study. As a proof of concept, two samples are investigated. The method is discussed on the basis of the obtained results.

Fabrication and thermal transient analysis of Ni-P sealed anodic aluminium oxide for electronic packaging

In recent years, suitable coatings on electronic packaging substrates are focused to improve heat-dissipation from the device hot spot. Nano porous-based anodic aluminum oxide (AAO) was introduced on Al surfaces aiming to improve heat dissipation. In extension, sealing of nano porous AAO using different deposition method is also introduced for thermal management. In this study, nickel–phosphorous (Ni-P) alloy was sealed and deposited on an already developed nanoporous anodic aluminum oxide (AAO) pattern using an electroless deposition method. The AAO is developed on Al5052 alloy using a two-step anodization process and the formation has resulted in 40- to 55-nm pore diameter and 6–7-μm thickness. The performance of Ni-P sealed nanoporous AAO was studied with respect to different deposition times and the characteristics have been studied via field emission scanning electron microscopy, X-ray diffraction, surface roughness profilometry, and thermal transient measurements. The thermal characteristics have been studied via thermal conductivity analyzer and thermal transient measurements. The resulting Ni-P layer has a cauliflower -like morphology with 1.2-μm layer thickness. The structural analysis show a mixture of amorphous and crystalline nature with sharp Ni peaks (111), (200) including the crystallite size as 518 nm. When compared with bare Al substrate, the 2-hr Ni-P sealing on AAO has a significant reduction in total thermal resistance (ΔRth) to 33%, rise in junction temperature (ΔTj) to 29%, and improved bulk thermal conductivity (k) to 41.5%. Results show enhanced properties of Ni-P-sealed AAO composite coating as a feasible option for the electronic packaging substrates.

Optimization-Based Network Identification for Thermal Transient Measurements

Network identification by deconvolution is a proven method for determining the thermal structure function of a given device. The method allows to derive the thermal capacitances as well as the resistances of a one-dimensional thermal path from the thermal step response of the device. However, the results of this method are significantly affected by noise in the measured data, which is unavoidable to a certain extent. In this paper, a post-processing procedure for network identification from thermal transient measurements is presented. This so-called optimization-based network identification provides a much more accurate and robust result compared to approaches using Fourier or Bayesian deconvolution in combination with Foster-to-Cauer transformation. The thermal structure function obtained from network identification by deconvolution is improved by repeatedly solving the inverse problem in a multi-dimensional optimization process. The result is a non-diverging thermal structure function, which agrees well with the measured thermal impedance. In addition, the associated time constant spectrum can be calculated very accurately. This work shows the potential of inverse optimization approaches for network identification.

Quantitative Performance Comparison of Thermal Structure Function Computations

The determination of thermal structure functions from transient thermal measurements using network identification by deconvolution is a delicate process as it is sensitive to noise in the measured data. Great care must be taken not only during the measurement process but also to ensure a stable implementation of the algorithm. In this paper, a method is presented that quantifies the absolute accuracy of network identification on the basis of different test structures. For this purpose, three measures of accuracy are defined. By these metrics, several variants of network identification are optimized and compared against each other. Performance in the presence of noise is analyzed by adding Gaussian noise to the input data. In the cases tested, the use of a Bayesian deconvolution provided the best results.

Impact of Cooling Injection on Shock Wave Over a Flat Tip in High Pressure Turbine

AbstractCooling design of highly loaded turbine blade tips is challenged by the scarcity of experimental data and the lack of physical understanding in cooling and overtip leakage (OTL) interaction under transonic conditions. To address these issues, this paper carried out transient thermal measurements through infrared thermography on a transonic flat tip with and without cooling injection. Experimental data of Nusselt number and cooling effectiveness were obtained and compared with computational fluid dynamics (CFD) results for numerical validation. Both experimental data and simulation results show that cooling injection drastically augments tip Nusselt number near pressure side (PS) which is upstream of ejection, and in areas around coolant holes. Moreover, a strikingly low Nusselt number stripe is observed downstream of cooling injection from one of the holes in aft portion of blade. The strip is directed transverse to local OTL streamline flowing from pressure to suction side (SS) and sprawls to adjacent coolant wakes. Further numerical analyses concluded that cooling injection changes tip aerodynamics and overtip shock wave structure fundamentally. Oblique shock waves across the uncooled flat tip are replaced by a confined shock train downstream of cooling injection and between cooling holes, which is constituted by two shocks normal to local OTL flow coming from pressure side. Across the first shock, density and pressure increases abruptly, contributing to thickening of tip boundary layer and the plummet of skin friction on tip surface, which is responsible for the sharp decline of tip Nusselt number and therefore, formation of low heat transfer stripe downstream cooling injection.

Dynamic Thermal Characterization of MEMS Electrothermal Actuators in Air

Dynamic performance of microelectromechanical system (MEMS) electrothermal actuators is directly determined by thermal principle and thermal characteristics at microscale differed from macroscale. To study and deeply understand the heat transfer mechanism and dynamic behavior of the MEMS electrothermal actuators, dynamic thermal measurements of a U-shaped thermal actuator and its array are implemented in air by using an infrared thermal microscope system with high spatial resolution. Both the steady-state, transient and frequency response thermal measurements are thoroughly carried out for the actuators. The temperature distribution, heating and cooling performances, and frequency response at different waveform voltages are analyzed and discussed. Furthermore, the electro-thermo-structural coupling model is established and the simulated results are compared with the measured results including steady-state, transient and frequency response thermal performances. By qualitative and quantitative comparisons, the simulated results are in fairly good agreement with the measured results.