Journal of Electronic Packaging

Journal Information
ISSN / EISSN : 1043-7398 / 1528-9044
Published by: ASME International (10.1115)
Total articles ≅ 2,035
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, Manojkumar Lokanathan, , , , Vaibhav Bahadur
Journal of Electronic Packaging; https://doi.org/10.1115/1.4052814

Abstract:
Machine learning (ML)-based predictive techniques are used in conjunction with a game-theoretic approach to predict the thermal behavior of a power electronics package and study the relative influence of encapsulation material properties and thermal management in influencing hotspot temperatures. Parametric steady-state and transient thermal simulations are conducted for a commercially available 1.2 kV/444 A SiC half-bridge module. An extensive databank of 2592 (steady-state) and 1200 (transient) data points generated via numerical simulations is used to train and evaluate the performance of three ML algorithms (random forest, support vector machine and neural network) in modeling the thermal behavior. The parameter space includes the thermal conductivities of the encapsulant, baseplate, heat sink and cooling conditions deployed at the sink; the parametric space covers a variety of materials and cooling scenarios. Excellent prediction accuracies with R2 values > 99.5% are obtained for the algorithms. SHAP (Shapley Additive exPlanations) dependence plots are used to quantify the relative impact of device and heat sink parameters on junction temperatures. We observe that while heatsink cooling conditions significantly influence the steady-state junction temperature, their contribution in determining the junction temperature in dynamic mode is diminished. Using ML-SHAP models, we quantify the impact of emerging polymeric nanocomposites (with high conductivities and diffusivities) on hotspot temperature reduction, with the device operating in static and dynamic modes. Overall, this study highlights the attractiveness of ML-based approaches for thermal design, and provides a framework for setting targets for future encapsulation materials.
Journal of Electronic Packaging; https://doi.org/10.1115/1.4052790

Abstract:
Boiling heat transfer has been a popular topic for decades because of its ability to remove a significant amount of thermal energy while maintaining a low wall superheat during the liquid phase change. Such boiling mechanisms can be tailored by engineering new boiling substrates through surface wettability modification and/or microscale feature installation. Here, we create new types of heterogeneous boiling surfaces that integrate vertical gradient micropores on macroscale fins by using a template-free electrodeposition method. The gradient morphology and corresponding gradient wettability simultaneously enable bubble nucleation on the top pores and capillary wicking through the bottom pores. With these unique wetting characteristics, we find that the gradient pores installed at the trench bottom demonstrate the most significant boiling enhancement in critical heat flux and heat transfer coefficients by 160% and 600%, respectively. This enhancement can be attributed to the microflow-enhanced nature of bubble departures around the fins while isolating bubble nucleation and liquid supply through gradient pores. These results provide fundamental insights into boiling mechanisms using porous media and the potential for future works that can optimize the design of multi-dimensional heterogeneous surfaces to engineer flow patterns and boiling mechanisms accordingly.
Journal of Electronic Packaging; https://doi.org/10.1115/1.4052767

Abstract:
The present study is focused on the experimental characterization of two-phase heat transfer performance and pressure drops within an ultra-compact heat exchanger (UCHE) suitable for electronics cooling applications. The UCHE is composed of a double-side-copper finned plate with an optimized geometry that enhances the heat transfer performance and flow stability, while minimizing the pressure drops. These features make the UCHE the ideal component for thermosyphon cooling systems, where low pressure drops are required to achieve high passive flow circulation rates and thus achieve high critical heat flux values. The UCHE's thermal-hydraulic performance is first evaluated in a pump-driven system at the Laboratory of Heat and Mass Transfer (LTCM-EPFL), where experiments include many configurations and operating conditions. Then, the UCHE is installed and tested as the condenser of a thermosyphon loop that rejects heat to a pumped refrigerant system at Nokia Bell Labs, in which both sides operate with refrigerants in phase change (condensation-to-boiling). Experimental results demonstrate high thermal performance with a maximum heat dissipation density of 5455 (kW/m3/K), which is significantly larger than conventional air-cooled heat exchangers and liquid-cooled small pressing depth brazed plate heat exchangers. Finally, a thermal performance analysis is presented that provides guidelines in terms of heat density dissipations at the server- and rack-level when using passive two-phase cooling.
Journal of Electronic Packaging, Volume 143; https://doi.org/10.1115/1.4052532

Abstract:
As the size, weight, and performance requirements of electronic devices grow increasingly demanding, their packaging has become more compact. As a result of thinning or removing the intermediate heat spreading layers, nonuniform heat generation from the chip-scale and component-level variations may be imposed directly on the attached microchannel heat sink. Despite the important heat transfer performance implications, the effect of uneven heating on the flow distribution in parallel microchannels undergoing boiling has been largely unexplored. In this study, a two-phase flow distribution model is used to investigate the impact of uneven heating on the flow distribution behavior of parallel microchannels undergoing boiling. Under lateral uneven heating (i.e., the channels are each heated to different levels, but the power input is uniform along the length of any given channel), it is found that the flow is significantly more maldistributed compared to the even heating condition. Specifically, the range of total flow rates over which the flow is maldistributed is broader and the maximum severity of flow maldistribution is higher. These trends are assessed as a function of the total input power, degree of uneven heating, and the extent of thermal connectedness between the channels. The model predictions are validated against experiments for a representative case of thermally isolated and coupled channels subjected to even heating and extreme lateral uneven heating conditions and show excellent agreement.
Journal of Electronic Packaging; https://doi.org/10.1115/1.4052750

Abstract:
The demand for wearable consumer electronics, fitness accessories and biomedical equipment has led to the growth research and development of thin flexible batteries. Wearable equipment and other asset monitoring applications require conformal installation of power sources on non-planar surfaces. For power sources in wearable electronics, durability to sustain repetitive mechanical stresses induced by human body motion is paramount along with the usual desirable power source characteristics. Previous research documenting the reliability of statically and dynamically folded power sources is scarce and does not follow standardized test protocols. Particularly, the use of manual stressing for mechanical folding of the power sources instead of a mechanical test setup is a key shortcoming in existing literature. Data is lacking on battery life cycling and in-situ mechanical stress-testing of the power sources including their impact of performance and reliability. Present study aims to overcome these deficiencies by testing a commercial Li-ion power source under static as well as dynamic folding. Furthermore, the fold-orientation and its fold-speed are varied to evaluate the effect of different mechanical stress topologies on the power source. Finally, a regression model was developed to capture the effect of these use parameters on battery capacity degradation.
Journal of Electronic Packaging, Volume 143; https://doi.org/10.1115/1.4052465

Abstract:
Over the last several decades, cooling technologies have been developed to address the growing thermal challenges associated with high-powered electronics. However, within the next several years, the heat generated by these devices is predicted to exceed 1 kW/cm2, and traditional methods, such as air cooling, are limited in their capacities to dissipate such high heat fluxes. In contrast, two-phase cooling methods, such as microdroplet evaporation, are very promising due to the large latent heat of vaporization associated with the phase change process. Previous studies have shown that nonaxisymmetric droplets have different evaporation characteristics than spherical droplets. The solid–liquid and liquid–vapor interfacial areas, volume, contact angle, and thickness of a droplet confined atop a micropillar are the primary parameters that influence evaporative heat transport. These parameters have a strong influence on both the conduction and diffusion resistance during the evaporation process. For example, a droplet with a higher liquid–vapor interfacial area will favorably increase heat transfer. Increased droplet thickness, on the other hand, has a detrimental influence on the evaporation rate. The dimensions of these droplets will vary in response to changes in each of the aforementioned parameters. Lowering the droplet thickness can be achieved by decreasing the liquid volume while maintaining a constant solid–liquid area. However, if the solid–liquid area and volume vary simultaneously, the average droplet thickness may increase, decrease, or remain constant. Furthermore, changes in the shape of the droplet modify the local equilibrium contact angle of the droplet for different azimuthal angles. As a result, the optimal combination of these parameters must be identified to maximize the heat transfer performance of an evaporating microdroplet. These droplet parameters can be manipulated by selecting different micropillar cross sections. In this work, we develop a shape optimization tool using the particle swarm optimization algorithm to maximize evaporation from a droplet confined atop a micropillar. The tool is used to optimize the shape of a nonaxisymmetric droplet. Compared to droplets atop circular and regular equilateral triangular micropillar structures, we find that droplets confined on pseudo-triangular micropillar structures have 23.7% and 5.7% higher heat transfer coefficients, respectively. The results of this work will advance the design of microstructures that support droplets with maximum heat transfer performance.
Journal of Electronic Packaging; https://doi.org/10.1115/1.4052711

Abstract:
In order to meet increasing performance demand from high-performance computing (HPC) and edge computing, thermal design power (TDP) of CPU and GPU needs to increase. This creates thermal challenge to corresponding electronic packages with respect to heat dissipation. In order to address this challenge, two-phase immersion cooling is gaining attention as its primary mode of heat of removal is via liquid-to-vapor phase change, which can occur at relatively low and constant temperatures. In this paper, integrated heat spreader (IHS) with boiling enhancement features is proposed. 3D metal printing and metal injection molding (MIM) are the two approaches used to manufacture the new IHS. The resultant IHS with enhancement features are used to build test vehicles (TV) by following standard electronic package assembly process. Experimental results demonstrated that boiling enhanced TVs improved two-phase immersion cooling capability by over 50% as compared to baseline TV without boiling enhanced features.
, Madhu Kasturi, Haotian Wu, , Edward Davis
Journal of Electronic Packaging; https://doi.org/10.1115/1.4052715

Abstract:
Automotive underhood electronics are subjected to high operating temperatures in the neighborhood of 150 to 200? for prolonged periods in the neighborhood of 10-years. Consumer grade off-the shelf electronics are designed to operate at 55 to 85? with a lower use-life of 3 to 5 years. Underfill materials are used to provide supplemental restraint to fine-pitch area array electronics and meet the reliability requirements. In this paper, a number of different underfill materials are subjected to automotive underhood temperatures to study the effect of long time isothermal exposure on microstructure and dynamic-mechanical properties. It has been shown that isothermal aging oxidizes the underfill, which can change the mechanical properties of the material significantly. The oxidation of underfill was studied experimentally by measuring oxidation layer thickness using polarized optical microscope. The effect on the mechanical properties was studied using the dynamic mechanical properties of underfill with DMA (Dynamic Mechanical Analyzer). Two different underfill materials were subjected to three different isothermal exposure, which are below, near and above the glass transition temperature of the underfills. The dynamic mechanical viscoelastic properties like storage modulus, loss modulus, tan delta and their respective glass transition temperatures were investigated. Three point bending mode was used in the DMA with a frequency of 1 Hz operating at 3?/min.
Journal of Electronic Packaging; https://doi.org/10.1115/1.4052716

Abstract:
Saturated water at one atmosphere pressure was boiled on horizontal copper discs of diameters 1.0,1.5 and 2.0 cm. respectively. The contact angle was varied from 10 to 80 degrees by controlling thermal oxidation of the discs, while the surrounding vessel size was changed by placing glass tubes of different inner diameters around the discs. Nucleate boiling heat transfer data were obtained up to critical heat flux (CHF), where vapor removal patterns were photographed. Dominant wavelengths at vapor jet interface and vapor jet diameters were measured from the photographs of the well wetted discs. For a well wetted surface, the magnitude of CHF increased when the heater size was reduced from 2.0 to 1.0 cm. Improving the wettability enhanced the CHF substantially, whereas the increased size of the liquid holding vessel had a smaller effect. The highest measured CHF is 233 W/cm2 or 2.11 times Zuber's CHF prediction for infinite horizontal flat plates. It was obtained on a 1.0 cm. disc of contact angle about 10 degrees surrounded by a large vessel. The CHF for this surface was increased from 201 to 233 W/cm2 when the ratio of heater size to surrounding vessel size was reduced from 1 to about 0.
Journal of Electronic Packaging; https://doi.org/10.1115/1.4052669

Abstract:
High temperature silicon carbide (SiC) die are the most critical and expensive component in electric vehicle (EV) power electronic packages and require both active and passive methods to dissipate heat during transient operation. The use of phase change materials (PCMs) to control the peak junction temperature of the SiC die and to buffer the temperature fluctuations in the package during simulated operation is modeled here. The latent heat storage potential of multiple PCM and PCM composites are explored in both single-sided and dual-sided package configurations. The results of this study show that the addition of phase change material (PCM) into two different styles of power electronics (PE) packages is an effective method for controlling the transient junction temperatures experienced during two different drive cycles. The addition of PCM in a single-sided package also serves to decrease temperature fluctuations experienced and may be used to reduce the necessary number of SiC die required for EVs, lowering the overall material cost and volume of the package by over 50%. PCM in a single-sided package may be nearly as effective as the double-sided cooling approach of a dual-sided package in the reduction of both peak junction temperature of SiC as well as controlling temperature variations between package layers.
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