Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.7991853
Thomas L. Rougher, Luke Yates, Zhe Cheng, B. Cola, S. Graham, Ramez Chaeito, A. Sood, M. Ashegi, K. Goodson
Diamond has the highest known thermal conductivity of any known bulk material, but the properties of synthetic diamond films often fall far short of this high level. The DARPA program Thermal Transport in Diamond Films for Electronics Thermal Management brings together researchers from five universities to comprehensively characterize the thermal transport and material properties of CVD diamond thin films in an effort to better how to further improve the thermal transport properties and understand how accurately these properties can be measured using time domain thermoreflectance and Raman spectroscopy. Here we summarize the results of the thermal measurements of diamond conducted via time domain thermoreflectance (TDTR) using two different systems and discuss some difficulties of accurately measuring the thermal conductivity of micron-thick anisotropic films that often have high surface roughness. We also report that in certain cases the thermal conductivity and thermal boundary conductance of CVD diamond films has been improved to the point of making them highly attractive for thermal management of high power electronic devices.
{"title":"Experimental considerations of CVD diamond film measurements using time domain thermoreflectance","authors":"Thomas L. Rougher, Luke Yates, Zhe Cheng, B. Cola, S. Graham, Ramez Chaeito, A. Sood, M. Ashegi, K. Goodson","doi":"10.1109/ITHERM.2017.7991853","DOIUrl":"https://doi.org/10.1109/ITHERM.2017.7991853","url":null,"abstract":"Diamond has the highest known thermal conductivity of any known bulk material, but the properties of synthetic diamond films often fall far short of this high level. The DARPA program Thermal Transport in Diamond Films for Electronics Thermal Management brings together researchers from five universities to comprehensively characterize the thermal transport and material properties of CVD diamond thin films in an effort to better how to further improve the thermal transport properties and understand how accurately these properties can be measured using time domain thermoreflectance and Raman spectroscopy. Here we summarize the results of the thermal measurements of diamond conducted via time domain thermoreflectance (TDTR) using two different systems and discuss some difficulties of accurately measuring the thermal conductivity of micron-thick anisotropic films that often have high surface roughness. We also report that in certain cases the thermal conductivity and thermal boundary conductance of CVD diamond films has been improved to the point of making them highly attractive for thermal management of high power electronic devices.","PeriodicalId":387542,"journal":{"name":"2017 16th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"118 1-2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114030873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.7992539
S. D. Marshall, R. Arayanarakool, L. Balasubramaniam, Bing Li, P. Lee, Peter C. Y. Chen
In order to improve upon a conventional straight microchannel heat sink, a range of curved, angular and wavy microchannels were designed in order to increase fluid mixing via the occurrence of secondary flow interactions, in particular Dean vortices, hence augmenting heat transport. Both numerical models conducted in FLUENT and laboratory experiments were employed to investigate the heat transfer enhancement of a range of geometries (single curved, wavy, sawtooth, U-turn and square-wave). In both studies, every channel demonstrated significantly higher Nusselt Numbers and Thermal Performance Factors (TPF) than an equivalent straight channel, despite an increase in pressure drop. The relative order of the channels in terms of TPF was the same for both experiments and numerical simulations, with the exception of the U-turn channel which performed better in the former. However, experimental TPF results were found to be 15–20% of those from the simulation — these differences are associated with the relative simplicity of the numerical model and additional non-linear impacts in the experiments. Overall, wavy channels were found to have superior performance, especially over angular channels with sharp turns, thus it is suggested that wavy microchannels are the most advantageous designs for the development of heat sinks, especially in terms of minimising pressure drop whilst still making use of the enhanced heat transfer properties of Dean vortices. Finally, for a given wavy channel, an optimal input flow rate condition is also determined.
{"title":"Heat exchanger improvement via curved, angular and wavy microfluidic channels: A comparison of numerical and experimental results","authors":"S. D. Marshall, R. Arayanarakool, L. Balasubramaniam, Bing Li, P. Lee, Peter C. Y. Chen","doi":"10.1109/ITHERM.2017.7992539","DOIUrl":"https://doi.org/10.1109/ITHERM.2017.7992539","url":null,"abstract":"In order to improve upon a conventional straight microchannel heat sink, a range of curved, angular and wavy microchannels were designed in order to increase fluid mixing via the occurrence of secondary flow interactions, in particular Dean vortices, hence augmenting heat transport. Both numerical models conducted in FLUENT and laboratory experiments were employed to investigate the heat transfer enhancement of a range of geometries (single curved, wavy, sawtooth, U-turn and square-wave). In both studies, every channel demonstrated significantly higher Nusselt Numbers and Thermal Performance Factors (TPF) than an equivalent straight channel, despite an increase in pressure drop. The relative order of the channels in terms of TPF was the same for both experiments and numerical simulations, with the exception of the U-turn channel which performed better in the former. However, experimental TPF results were found to be 15–20% of those from the simulation — these differences are associated with the relative simplicity of the numerical model and additional non-linear impacts in the experiments. Overall, wavy channels were found to have superior performance, especially over angular channels with sharp turns, thus it is suggested that wavy microchannels are the most advantageous designs for the development of heat sinks, especially in terms of minimising pressure drop whilst still making use of the enhanced heat transfer properties of Dean vortices. Finally, for a given wavy channel, an optimal input flow rate condition is also determined.","PeriodicalId":387542,"journal":{"name":"2017 16th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122895544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.7992556
Sevket U. Yuruker, Daniel G. Bae, R. Mandel, Bao Yang, P. McCluskey, A. Bar-Cohen, M. Ohadi
Two-phase microchannel cooling has demonstrated substantial performance enhancement for thermal management of high-power electronics, offering remarkable heat removal capability without imposing high pumping power penalties. However, similar to other bulk cooling methods, this method alone too has difficulty in addressing remediation of local hotspots. Thermoelectric coolers, on the other hand, are scalable and perfectly suited for localized cooling. Thus in this paper, we report our work on integration of a micro-contact enhanced TEC with FEEDS (thin-Film Evaporation and Enhanced fluid Delivery System) manifold-micro channel system. Combining these two thermal management schemes into a single system can provide effective heat removal over the entire electronic chip surface. Integration of these two methods, however, poses several challenges, including hermetic sealing, wiring of the TEC, excessive joule heating in electrical traces, and thermal/electrical short-circuits. Thus, the aim of this study was to integrate an optimized, 3 mm × 0.8 mm TEC into a FEEDS manifold-microchannel system to create a reliable high flux cooling mechanism on a silicon or silicon carbide chip for cooling of 5kW/cm2 hotspot and 1kW/cm2 background heat fluxes. The manufacturing, integration configuration, and assembly of the system are discussed in this paper. A numerical model of the system is built and simulated using the commercial finite-element analysis software ANSYS. Preliminary numerical results demonstrated that with 30 °C temperature rise at the SiC chip's background surface, less than 35 °C hotspot temperature rise with respect to the coolant fluid temperature (110 °C) can be achieved.
两相微通道冷却已经证明了高功率电子产品的热管理性能的显著增强，在不施加高泵浦功率损失的情况下提供了卓越的散热能力。然而，与其他整体冷却方法类似，这种方法本身也难以解决局部热点的修复问题。另一方面，热电冷却器是可扩展的，非常适合局部冷却。因此，在本文中，我们报告了我们在集成微接触增强TEC与FEEDS(薄膜蒸发和增强流体输送系统)歧管-微通道系统的工作。将这两种热管理方案结合到一个系统中可以在整个电子芯片表面提供有效的散热。然而，这两种方法的集成带来了一些挑战，包括密封性、TEC的布线、电迹线中过多的焦耳加热以及热/电短路。因此，本研究的目的是将优化的3 mm × 0.8 mm TEC集成到FEEDS管汇-微通道系统中，在硅或碳化硅芯片上创建可靠的高通量冷却机制，以冷却5kW/cm2的热点和1kW/cm2的背景热流。本文讨论了该系统的制造、集成配置和装配。利用商用有限元分析软件ANSYS建立了系统的数值模型并进行了仿真。初步数值结果表明，SiC芯片背景表面升温30℃时，相对于冷却液温度(110℃)，热点温升可小于35℃。
{"title":"Integration of micro-contact enhanced thermoelectric cooler with a FEEDS manifold-microchannel system for cooling of high flux electronics","authors":"Sevket U. Yuruker, Daniel G. Bae, R. Mandel, Bao Yang, P. McCluskey, A. Bar-Cohen, M. Ohadi","doi":"10.1109/ITHERM.2017.7992556","DOIUrl":"https://doi.org/10.1109/ITHERM.2017.7992556","url":null,"abstract":"Two-phase microchannel cooling has demonstrated substantial performance enhancement for thermal management of high-power electronics, offering remarkable heat removal capability without imposing high pumping power penalties. However, similar to other bulk cooling methods, this method alone too has difficulty in addressing remediation of local hotspots. Thermoelectric coolers, on the other hand, are scalable and perfectly suited for localized cooling. Thus in this paper, we report our work on integration of a micro-contact enhanced TEC with FEEDS (thin-Film Evaporation and Enhanced fluid Delivery System) manifold-micro channel system. Combining these two thermal management schemes into a single system can provide effective heat removal over the entire electronic chip surface. Integration of these two methods, however, poses several challenges, including hermetic sealing, wiring of the TEC, excessive joule heating in electrical traces, and thermal/electrical short-circuits. Thus, the aim of this study was to integrate an optimized, 3 mm × 0.8 mm TEC into a FEEDS manifold-microchannel system to create a reliable high flux cooling mechanism on a silicon or silicon carbide chip for cooling of 5kW/cm2 hotspot and 1kW/cm2 background heat fluxes. The manufacturing, integration configuration, and assembly of the system are discussed in this paper. A numerical model of the system is built and simulated using the commercial finite-element analysis software ANSYS. Preliminary numerical results demonstrated that with 30 °C temperature rise at the SiC chip's background surface, less than 35 °C hotspot temperature rise with respect to the coolant fluid temperature (110 °C) can be achieved.","PeriodicalId":387542,"journal":{"name":"2017 16th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115049240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.7992606
A. Hamed, S. Ndao
Probably the most trending technology in electronics today is wearable and flexible electronics. Flexible electronics are electronic circuits fabricated on flexible surfaces and offer many advantages. Similar to conventional electronics, thermal management of flexible electronics is a formidable challenge. In addition to high heat fluxes from the miniaturization of electronics' components, thermal management of flexible electronics must be adapted to the flexible and stretchable nature of the technology. In this work, we numerically study the thermal performance of thin film liquid metal PCMs for the thermal management of flexible electronics. Using 1-D (axial direction) transient conduction along with the enthalpy method, the temperature distribution within the liquid metal PCM was investigated as a function of length, thermal properties, and unsteady heat load. The results showed the existence of three important regions within which there exists an optimal PCM configuration and operating condition. Because PCMs are most suited for transient heat load applications, which is the case for many electronics, we studied the effects of transient heat load's periodicity and duration on the thermal performance of the liquid metal PCMs. The results showed that with a base load resulting in a chip temperature just below the PCM's melting temperature, optimal periodic heat loads can be achieved to maintain the chip at an acceptable operating temperature.
{"title":"Modeling of writable thin film liquid metal phase change material for electronics cooling","authors":"A. Hamed, S. Ndao","doi":"10.1109/ITHERM.2017.7992606","DOIUrl":"https://doi.org/10.1109/ITHERM.2017.7992606","url":null,"abstract":"Probably the most trending technology in electronics today is wearable and flexible electronics. Flexible electronics are electronic circuits fabricated on flexible surfaces and offer many advantages. Similar to conventional electronics, thermal management of flexible electronics is a formidable challenge. In addition to high heat fluxes from the miniaturization of electronics' components, thermal management of flexible electronics must be adapted to the flexible and stretchable nature of the technology. In this work, we numerically study the thermal performance of thin film liquid metal PCMs for the thermal management of flexible electronics. Using 1-D (axial direction) transient conduction along with the enthalpy method, the temperature distribution within the liquid metal PCM was investigated as a function of length, thermal properties, and unsteady heat load. The results showed the existence of three important regions within which there exists an optimal PCM configuration and operating condition. Because PCMs are most suited for transient heat load applications, which is the case for many electronics, we studied the effects of transient heat load's periodicity and duration on the thermal performance of the liquid metal PCMs. The results showed that with a base load resulting in a chip temperature just below the PCM's melting temperature, optimal periodic heat loads can be achieved to maintain the chip at an acceptable operating temperature.","PeriodicalId":387542,"journal":{"name":"2017 16th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123693212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.7992469
Farah Singer, D. Deisenroth, David M. Hymas, M. Ohadi
Recently additive manufacturing (AM) has brought significant innovation to thermal management devices and electronics. Among the most influential innovations are additively manufactured copper/copper alloy components and composites that benefit from the superior thermal, electrical and structural properties of the material. Cu is widely used in electronics, HVACR, radiators, charge air coolers, brazed plate heat exchangers, and oil cooling. Ongoing research is extensively studying, in parallel, Cu properties/characteristics and the different AM process parameters required to enhance the quality of the manufactured Cu components and to optimize their performance/applications. In this paper, we report various AM techniques and AM-based hybrid processes used to produce high-density Cu components. Selective heat exchanger/thermal management applications progress is also reviewed. It is then shown that additively manufactured, dense Cu can generate low mass structures and polymer/metal composites that promise to revolutionize developments in thermal management applications. Studies on the effect of the material properties such as the Cu particle morphology and size distribution are also reported. The major studies that report using Cu to address the challenges of electronics fabrication and cooling, which directly affect system-level performance and reliability, are also discussed. A novel AM process that facilitates microchannel cooling with Cu structures and new processes that allow embedding copper wires into thermoplastic dielectric structures are discussed to further emphasize the potentially transformative advances in additively manufactured electronics and thermal management devices using Cu/Cu alloy composites.
{"title":"Additively manufactured copper components and composite structures for thermal management applications","authors":"Farah Singer, D. Deisenroth, David M. Hymas, M. Ohadi","doi":"10.1109/ITHERM.2017.7992469","DOIUrl":"https://doi.org/10.1109/ITHERM.2017.7992469","url":null,"abstract":"Recently additive manufacturing (AM) has brought significant innovation to thermal management devices and electronics. Among the most influential innovations are additively manufactured copper/copper alloy components and composites that benefit from the superior thermal, electrical and structural properties of the material. Cu is widely used in electronics, HVACR, radiators, charge air coolers, brazed plate heat exchangers, and oil cooling. Ongoing research is extensively studying, in parallel, Cu properties/characteristics and the different AM process parameters required to enhance the quality of the manufactured Cu components and to optimize their performance/applications. In this paper, we report various AM techniques and AM-based hybrid processes used to produce high-density Cu components. Selective heat exchanger/thermal management applications progress is also reviewed. It is then shown that additively manufactured, dense Cu can generate low mass structures and polymer/metal composites that promise to revolutionize developments in thermal management applications. Studies on the effect of the material properties such as the Cu particle morphology and size distribution are also reported. The major studies that report using Cu to address the challenges of electronics fabrication and cooling, which directly affect system-level performance and reliability, are also discussed. A novel AM process that facilitates microchannel cooling with Cu structures and new processes that allow embedding copper wires into thermoplastic dielectric structures are discussed to further emphasize the potentially transformative advances in additively manufactured electronics and thermal management devices using Cu/Cu alloy composites.","PeriodicalId":387542,"journal":{"name":"2017 16th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122996233","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.7992611
Pavan Rajmane, Hassaan Ahmad Khan, A. Doiphode, Unique Rahangdale, D. Agonafer, A. Lohia, S. Kummerl, L. Nguyen
Various studies have been conducted to study the effect of varying board thickness on thermo-mechanical reliability of BGA packages. Wafer level chip scale packages (WLCSP) have also been studied in this regard to determine the effect of PCB build-up thickness on the solder joint reliability [1]. The studies clearly demonstrate that the thinner Printed Circuit Boards (PCBs) result in longer thermo-mechanical fatigue life of solder joints for BGA. With the literature and past trends supporting the idea of thinner boards, manufacturer opted to move forward by decreasing the thickness of their PCBs to improve the reliability of their packages. The thickness was reduced from 1mm to 0.7mm by decreasing the thicknesses of individual layers and keeping the total number of layers constant. When subjected to thermal cycling, it was observed that 0.7mm board was failing earlier than the 1mm board. Since this behavior of a WLCSP contrasts with the past trends, it required extensive study to determine and understand the pre-mature physics of failure/causality of failure in 0.7mm board. In this paper, an effort is made to understand the mechanism which is causing an early failure in the thinner board. The effect of number & thicknesses of core layers, prepregs and Cu layers in the board has been studied through material characterization of both 1mm and 0.7mm boards. Further, a design optimization account has also been presented to improve the thermo-mechanical reliability of this package.
{"title":"Failure mechanisms of boards in a thin wafer level chip scale package","authors":"Pavan Rajmane, Hassaan Ahmad Khan, A. Doiphode, Unique Rahangdale, D. Agonafer, A. Lohia, S. Kummerl, L. Nguyen","doi":"10.1109/ITHERM.2017.7992611","DOIUrl":"https://doi.org/10.1109/ITHERM.2017.7992611","url":null,"abstract":"Various studies have been conducted to study the effect of varying board thickness on thermo-mechanical reliability of BGA packages. Wafer level chip scale packages (WLCSP) have also been studied in this regard to determine the effect of PCB build-up thickness on the solder joint reliability [1]. The studies clearly demonstrate that the thinner Printed Circuit Boards (PCBs) result in longer thermo-mechanical fatigue life of solder joints for BGA. With the literature and past trends supporting the idea of thinner boards, manufacturer opted to move forward by decreasing the thickness of their PCBs to improve the reliability of their packages. The thickness was reduced from 1mm to 0.7mm by decreasing the thicknesses of individual layers and keeping the total number of layers constant. When subjected to thermal cycling, it was observed that 0.7mm board was failing earlier than the 1mm board. Since this behavior of a WLCSP contrasts with the past trends, it required extensive study to determine and understand the pre-mature physics of failure/causality of failure in 0.7mm board. In this paper, an effort is made to understand the mechanism which is causing an early failure in the thinner board. The effect of number & thicknesses of core layers, prepregs and Cu layers in the board has been studied through material characterization of both 1mm and 0.7mm boards. Further, a design optimization account has also been presented to improve the thermo-mechanical reliability of this package.","PeriodicalId":387542,"journal":{"name":"2017 16th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128645058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The development of newer and more efficient cooling techniques to sustain the increasing power density of high-performance computing systems is becoming one of the major challenges in the development of microelectronics. In this framework, two-phase cooling is a promising solution for dissipating the greater amount of generated heat. In the present study an experimental investigation of two-phase flow boiling in a micro-pin fin evaporator is performed. The micro-evaporator has a heated area of 1 cm2 containing 66 rows of cylindrical in-line micro-pin fins with diameter, height and pitch of respectively 50 μm, 100 μm and 91.7 μm. At the entrance of the heated area an extra row of micro-pin fins with a larger diameter of 100 μm acts as inlet restrictions to avoid flow instabilities. The working fluid is R1234ze(E) tested over a wide range of conditions: mass fluxes varying from 750 kg/m2s to 1750 kg/m2s and heat fluxes ranging from 20 W/cm2 to 44 W/cm2 while maintaining a constant outlet saturation temperature of 35 °C. In order to assess the thermal-hydraulic performance of the current heat sink, the total pressure drops are directly measured, while local values of heat transfer coefficient are evaluated by coupling high speed flow visualization with infrared temperature measurements. According to the experimental results, the mass flux has the most significant impact on the heat transfer coefficient while heat flux is a less influential parameter. The vapor quality varies in a range between 0 and 0.45. The heat transfer coefficient in the subcooled region reaches a maximum value of about 12 kW/m2K, whilst in two-phase flow it goes up to 30 kW/m2K.
{"title":"Flow boiling heat transfer and pressure drops of R1234ze(E) in a silicon micro-pin fin evaporator","authors":"C. Falsetti, M. Magnini, J. Thome","doi":"10.1115/1.4037152","DOIUrl":"https://doi.org/10.1115/1.4037152","url":null,"abstract":"The development of newer and more efficient cooling techniques to sustain the increasing power density of high-performance computing systems is becoming one of the major challenges in the development of microelectronics. In this framework, two-phase cooling is a promising solution for dissipating the greater amount of generated heat. In the present study an experimental investigation of two-phase flow boiling in a micro-pin fin evaporator is performed. The micro-evaporator has a heated area of 1 cm2 containing 66 rows of cylindrical in-line micro-pin fins with diameter, height and pitch of respectively 50 μm, 100 μm and 91.7 μm. At the entrance of the heated area an extra row of micro-pin fins with a larger diameter of 100 μm acts as inlet restrictions to avoid flow instabilities. The working fluid is R1234ze(E) tested over a wide range of conditions: mass fluxes varying from 750 kg/m2s to 1750 kg/m2s and heat fluxes ranging from 20 W/cm2 to 44 W/cm2 while maintaining a constant outlet saturation temperature of 35 °C. In order to assess the thermal-hydraulic performance of the current heat sink, the total pressure drops are directly measured, while local values of heat transfer coefficient are evaluated by coupling high speed flow visualization with infrared temperature measurements. According to the experimental results, the mass flux has the most significant impact on the heat transfer coefficient while heat flux is a less influential parameter. The vapor quality varies in a range between 0 and 0.45. The heat transfer coefficient in the subcooled region reaches a maximum value of about 12 kW/m2K, whilst in two-phase flow it goes up to 30 kW/m2K.","PeriodicalId":387542,"journal":{"name":"2017 16th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"205 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116390945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.7992639
Nianjun Fu, J. Suhling, S. Hamasha, P. Lall
When exposed to a temperature changing environment, solder joints in electronic assemblies are subjected to cyclic thermal-mechanical loading due to the mismatches in coefficients of thermal expansion (CTE) of the different assembly materials. Eventually, the cyclic loading can result in fatigue failure of solder joints, which is one of the common failure modes in electronic packaging. While it has been known that the reversal of inelastic strain can change the stress-strain behavior of materials (Bauschinger effect), there have been few prior studies on how the cycling changes the microstructure and degrades the mechanical properties of lead free solders during fatigue testing. In this investigation, we have explored the effects of mechanical cycling on the cyclic stress-strain behavior (hysteresis loop area, plastic strain range, and peak stress) and on the constitutive behavior (stress-strain and creep) of SAC305 lead free solder in fatigue testing. At the same time, effects of cycling on solder microstructure have been studied. The goal of the study was to explore the damage accumulation that occurs during fatigue testing.
{"title":"Evolution of the cyclic stress-strain and constitutive behaviors of SAC305 lead free solder during fatigue testing","authors":"Nianjun Fu, J. Suhling, S. Hamasha, P. Lall","doi":"10.1109/ITHERM.2017.7992639","DOIUrl":"https://doi.org/10.1109/ITHERM.2017.7992639","url":null,"abstract":"When exposed to a temperature changing environment, solder joints in electronic assemblies are subjected to cyclic thermal-mechanical loading due to the mismatches in coefficients of thermal expansion (CTE) of the different assembly materials. Eventually, the cyclic loading can result in fatigue failure of solder joints, which is one of the common failure modes in electronic packaging. While it has been known that the reversal of inelastic strain can change the stress-strain behavior of materials (Bauschinger effect), there have been few prior studies on how the cycling changes the microstructure and degrades the mechanical properties of lead free solders during fatigue testing. In this investigation, we have explored the effects of mechanical cycling on the cyclic stress-strain behavior (hysteresis loop area, plastic strain range, and peak stress) and on the constitutive behavior (stress-strain and creep) of SAC305 lead free solder in fatigue testing. At the same time, effects of cycling on solder microstructure have been studied. The goal of the study was to explore the damage accumulation that occurs during fatigue testing.","PeriodicalId":387542,"journal":{"name":"2017 16th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124202225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.7992546
David M. Hymas, Martinus A. Arle, Farah Singer, A. Shooshtari, M. Ohadi
The present study builds upon our prior work in integrating additive manufacturing into next-generation heat/mass exchanger devices. In this paper, we will report an analysis of the fabrication, testing, and performance of an additively manufactured polymer composite heat exchanger. This heat exchanger utilizes a novel approach to achieve enhanced air-side heat transfer coefficients and overall mass reduction. This device relies on the Cross-Media Fiber concept where two fluid flows are thermally linked by high-conductivity fins, passing through a low-conductivity channel wall. Through this, the authors have met the required pressure containment, coefficient of performance, and heat flow rate targets, which were 28 psig, 100 and 150 W respectively. The advances that are discussed throughout this paper have allowed this novel polymer composite heat exchanger to be produced through a newly developed form of additive manufacturing that can potentially lead to the economical production of large scale Cross-Media Fiber heat exchangers.
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Pub Date : 2017-05-01DOI: 10.1109/ITHERM.2017.8023956
M. Arie, A. Shooshtari, M. Ohadi
Additive manufacturing is a fast-growing technique due to its ability to fabricate complex objects layer by layer from a preprogrammed digital model. Additive manufacturing can greatly enhance the heat exchanger manufacturing field, as it makes possible the fabrication of complex heat exchanger designs that are challenging to fabricate using conventional methods. In the present work, an air-to-water manifold-microchannel heat exchanger made of titanium alloy (Ti64) with size of 15 cm x 15 cm x 3.2 cm was fabricated using direct metal laser sintering (DMLS) additive manufacturing technique. The manifoldmicrochannel feeds the fluid flow into an array of parallel microchannels for better flow distribution as well as short flow travel length, thus yielding significantly enhanced heat transfer performance with low pressure drop penalty. Upon successful fabrication, the heat exchanger was experimentally tested, and the results were analyzed against conventional heat transfer surfaces. Based on the experimental results, for the case where the heat exchanger heat flow rate is 900 W, air-side Reynolds number is less than 100 and the temperature difference between the inlet air and water temperature is 27.5°C, heat transfer coefficient of 180 W/m2K and pressure drop of 100 Pa are observed. Compared to the conventional surfaces like wavy fin, louvered fin, and plain plate fins, up to 80%, 120%, and 190% improvement in air-side heat transfer coefficients were recorded, respectively, with an air-side pressure drop of less than 100 Pa. The results strongly suggest that additive manufacturing could be implemented for materials and complex designs that are otherwise difficult to fabricate with conventional technologies.
增材制造是一种快速发展的技术，因为它能够从预编程的数字模型逐层制造复杂的物体。增材制造可以极大地增强热交换器制造领域，因为它可以制造复杂的热交换器设计，这是使用传统方法制造的挑战。本文采用直接金属激光烧结(DMLS)增材制造技术，制作了尺寸为15 cm x 15 cm x 3.2 cm的钛合金(Ti64)气-水歧管-微通道热交换器。多管式微通道将流体输送到一系列平行的微通道中，以实现更好的流动分配和更短的流动行程长度，从而显著提高传热性能，同时降低压降损失。在制造成功后，对换热器进行了实验测试，并将结果与传统的传热表面进行了分析。实验结果表明，当换热器热流量为900 W，空气侧雷诺数小于100，进水温差为27.5℃时，换热系数为180 W/m2K，压降为100 Pa。与传统的波纹翅片、百叶翅片和平面翅片等表面相比，空气侧传热系数分别提高了80%、120%和190%，而空气侧压降小于100 Pa。结果强烈表明，增材制造可以用于材料和复杂的设计，否则难以用传统技术制造。
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