Pub Date : 2016-05-01DOI: 10.1109/ITHERM.2016.7517530
R. Kanapady, Darryl Moore, A. Raghupathy, William Maltz
In this paper, influence of temperature gradient in interconnects due to Joule heating in 3D packaging on electromigration failure is presented. Black's Mean Time to Failure (MTF) model relates exponentially to the temperature of interconnects which is assumed to be constant hence does not take into account temperature gradient. The developed electromigration model incorporates the driving force due to temperature gradient in addition to the effects of current density, vacancy concentration gradients and stress gradients in the interconnects and due to coefficient of thermal expansion mismatch with surrounding materials. Effectiveness of the developed finite element model is illustrated complex C4 solder bumps of flip-chip packages using COMSOL Mutliphysics software. It is shown that for same current density in the complex C4 solder bumps of flip-chip packages it is possible that failure times could be lower for lower solder average temperature with higher temperature gradient than for higher solder temperature with low temperature gradient.
{"title":"Influence of temperature gradient on electromigration failures in 3D packaging","authors":"R. Kanapady, Darryl Moore, A. Raghupathy, William Maltz","doi":"10.1109/ITHERM.2016.7517530","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517530","url":null,"abstract":"In this paper, influence of temperature gradient in interconnects due to Joule heating in 3D packaging on electromigration failure is presented. Black's Mean Time to Failure (MTF) model relates exponentially to the temperature of interconnects which is assumed to be constant hence does not take into account temperature gradient. The developed electromigration model incorporates the driving force due to temperature gradient in addition to the effects of current density, vacancy concentration gradients and stress gradients in the interconnects and due to coefficient of thermal expansion mismatch with surrounding materials. Effectiveness of the developed finite element model is illustrated complex C4 solder bumps of flip-chip packages using COMSOL Mutliphysics software. It is shown that for same current density in the complex C4 solder bumps of flip-chip packages it is possible that failure times could be lower for lower solder average temperature with higher temperature gradient than for higher solder temperature with low temperature gradient.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117062762","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517645
Luis Silva-Llanca
In small scale applications, synthetic jets have proven to be an efficient cooling technique when impinged onto heating surfaces. These jets are produced by the quick injection-ejection of fluid from an orifice, which generates a train of counter-rotating vortex pairs that sustain a fluctuating jet flow with positive momentum. Previously, in an effort to understand the fundamental mechanisms that drive this phenomenon, an idealized numerical canonical geometry was created and studied using CFD, which liberated the jet from actuator artifacts. Due to its highly vortical nature, the fluid can penetrate the thermal boundary layer better than a conventional steady jet. In the wall jet region, the passing of the main vortices gives rise to secondary vortices with opposite rotation that cause the entrainment of cold fluid towards the vicinity of the heated surface, thus broadening the effective impinging area and further enhancing the heat transfer. This study intends to advance prior fundamental studies by focusing in the fluid dynamics associated with this type of flow. Counter-rotating viscous Lamb-Ossen vortex pairs were repeatedly placed inside a domain at a given time interval (frequency) with a given intensity. The method of images was used to replicate the presence of the perpendicular static surface that acts as an inviscid wall. A numerical code written in Matlab™ language was developed to calculate the unsteady interaction between the N vortices, and the consequently induced fluid flow. This was used to compare the approach proposed with the canonical CFD data. A method is proposed to predict the vortex intensity evolution, which presented excellent agreement with the numerical data. It was found that the Lamb-Ossen vortex pair translational velocity and trajectory were comparable to the synthetic jet in the free jet region. The canonical vortex slowed when entering the stagnation region due to wall effects and the presence of the secondary vortex that induced a velocity onto the primary vortex opposite to its translation. Four effects were identified, each having different or opposite relationships with the jet parameters and the heat transfer, providing multiple options when it comes to finding optimum operating conditions.
{"title":"Replicating impinging synthetic jets as a train of consecutive viscous Lamb-Ossen vortex pairs","authors":"Luis Silva-Llanca","doi":"10.1109/ITHERM.2016.7517645","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517645","url":null,"abstract":"In small scale applications, synthetic jets have proven to be an efficient cooling technique when impinged onto heating surfaces. These jets are produced by the quick injection-ejection of fluid from an orifice, which generates a train of counter-rotating vortex pairs that sustain a fluctuating jet flow with positive momentum. Previously, in an effort to understand the fundamental mechanisms that drive this phenomenon, an idealized numerical canonical geometry was created and studied using CFD, which liberated the jet from actuator artifacts. Due to its highly vortical nature, the fluid can penetrate the thermal boundary layer better than a conventional steady jet. In the wall jet region, the passing of the main vortices gives rise to secondary vortices with opposite rotation that cause the entrainment of cold fluid towards the vicinity of the heated surface, thus broadening the effective impinging area and further enhancing the heat transfer. This study intends to advance prior fundamental studies by focusing in the fluid dynamics associated with this type of flow. Counter-rotating viscous Lamb-Ossen vortex pairs were repeatedly placed inside a domain at a given time interval (frequency) with a given intensity. The method of images was used to replicate the presence of the perpendicular static surface that acts as an inviscid wall. A numerical code written in Matlab™ language was developed to calculate the unsteady interaction between the N vortices, and the consequently induced fluid flow. This was used to compare the approach proposed with the canonical CFD data. A method is proposed to predict the vortex intensity evolution, which presented excellent agreement with the numerical data. It was found that the Lamb-Ossen vortex pair translational velocity and trajectory were comparable to the synthetic jet in the free jet region. The canonical vortex slowed when entering the stagnation region due to wall effects and the presence of the secondary vortex that induced a velocity onto the primary vortex opposite to its translation. Four effects were identified, each having different or opposite relationships with the jet parameters and the heat transfer, providing multiple options when it comes to finding optimum operating conditions.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"239 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124293225","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517715
H. Alissa, K. Nemati, B. Sammakia, M. Seymour, Russell Tipton, Tom Wu, Ken Schneebeli
In this investigation, we utilize a new method of characterization in which IT airflow systems are ranked from a 1RU ToR switches, xRU servers to 9RU Blade Center. The free delivery (FD) and the critical pressure (Pc) are unique properties of each IT airflow system, satisfying its active flow curve (AFC). Those curves are used in previously validated models to investigate the interaction of IT with different air systems in a confined space. A validated model of containment is studied of a CAC aisle from Binghamton University data center lab. It is shown that reverse flow can take place in an operating piece of IT with weaker air system; this can endanger IT reliability and up time at different data center events. This can also change previous conclusions about the ride through time in well-sealed fully contained systems. Another important finding is that design containment systems based on the assumption of uniform load in the aisle/cabinet is a misconception that can endanger facility operation. In general, the reduction in airflow rate upon events in the data center (DC) is a function of each IT air system. To our knowledge, this is the first time in literature where both recent models of IT active flow curves and black box thermal inertia are combined to yield realistic failure analysis of contained solutions.
{"title":"On reliability and uptime of IT in contained solution","authors":"H. Alissa, K. Nemati, B. Sammakia, M. Seymour, Russell Tipton, Tom Wu, Ken Schneebeli","doi":"10.1109/ITHERM.2016.7517715","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517715","url":null,"abstract":"In this investigation, we utilize a new method of characterization in which IT airflow systems are ranked from a 1RU ToR switches, xRU servers to 9RU Blade Center. The free delivery (FD) and the critical pressure (Pc) are unique properties of each IT airflow system, satisfying its active flow curve (AFC). Those curves are used in previously validated models to investigate the interaction of IT with different air systems in a confined space. A validated model of containment is studied of a CAC aisle from Binghamton University data center lab. It is shown that reverse flow can take place in an operating piece of IT with weaker air system; this can endanger IT reliability and up time at different data center events. This can also change previous conclusions about the ride through time in well-sealed fully contained systems. Another important finding is that design containment systems based on the assumption of uniform load in the aisle/cabinet is a misconception that can endanger facility operation. In general, the reduction in airflow rate upon events in the data center (DC) is a function of each IT air system. To our knowledge, this is the first time in literature where both recent models of IT active flow curves and black box thermal inertia are combined to yield realistic failure analysis of contained solutions.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"70 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124407370","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517633
Qi Chen, Run Hu, Bin Xie, Yue Xingjian, Jingjing Cheng, Xiaobing Luo
In our previous study, we investigated the effects of different packaging materials (silicone and phosphor layer) on the reliability of high power light-emitting diodes (HPLEDs) by highly accelerated stress test (HAST). The experimental results showed that the LED samples' lumen maintenance property might have dependence on the silicone amount in the package. In this paper, we further studied the effect of silicone amount on the lumen maintenance under HAST. Five categories of LED specimens specified by silicone amount were prepared and subjected to an isothermal chamber whose temperature was set at 125 °C. An online testing system was used to monitor and record the light outputs in real time during the experimental process. After 400 hours of aging, the largest attenuating range reached 6.17% and different groups display different degradation behaviors. An exponential decay model was adopted to calculate the decay rate of each lumen maintenance curve. The decay rate differs as the silicone amount inside the package modules changes. This phenomenon is well explained and Monte Carlo ray-tracing simulations are carried out to validate the explanation. The interaction effect of both silicone amount and temperature is also found and more researches need to be done for further study.
{"title":"Effect study of silicone amount on the lumen maintenance of high power LED under accelerated stress test","authors":"Qi Chen, Run Hu, Bin Xie, Yue Xingjian, Jingjing Cheng, Xiaobing Luo","doi":"10.1109/ITHERM.2016.7517633","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517633","url":null,"abstract":"In our previous study, we investigated the effects of different packaging materials (silicone and phosphor layer) on the reliability of high power light-emitting diodes (HPLEDs) by highly accelerated stress test (HAST). The experimental results showed that the LED samples' lumen maintenance property might have dependence on the silicone amount in the package. In this paper, we further studied the effect of silicone amount on the lumen maintenance under HAST. Five categories of LED specimens specified by silicone amount were prepared and subjected to an isothermal chamber whose temperature was set at 125 °C. An online testing system was used to monitor and record the light outputs in real time during the experimental process. After 400 hours of aging, the largest attenuating range reached 6.17% and different groups display different degradation behaviors. An exponential decay model was adopted to calculate the decay rate of each lumen maintenance curve. The decay rate differs as the silicone amount inside the package modules changes. This phenomenon is well explained and Monte Carlo ray-tracing simulations are carried out to validate the explanation. The interaction effect of both silicone amount and temperature is also found and more researches need to be done for further study.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121292436","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517543
H. Su, Ye Li
In this study, an oscillating sheet array device driven by electromagnetic force has been proposed. This device can be integrated with a heat sink to enhance heat transfer coefficient. Typically, the fin gaps of a heat sink for natural convection need to be sparse. If the fin gaps are large enough, the boundary layers that develop along the surface of the fins will not overlap and result in optimal performance. Since the fin gaps are sparse, it is allowed to insert an oscillating sheet between the gaps. They can produce airflow and break boundary layers to enhance heat transfer coefficient. The dimension of the heat sink under study with nine fins is 80 mm (L) * 80 mm (W) * 50 mm (H) and the fin gaps are 8 mm. The main advantages of the oscillating sheet array are no bearing structure and small volume change - it only increases the total heat sink volume by 0.6%. Moreover, its simplicity makes it a highly reliable and low cost device. The driving current can be either DC PWM or AC between 3 V - 12 V so it is compatible with most electronic devices. According to the cooling experiment, vertically arranged array can decrease the thermal resistance of the tested heat sink from 3.41 to 1.61 while consuming 0.66 W.
本文提出了一种由电磁力驱动的振荡片阵列器件。该装置可与散热器集成，以提高传热系数。通常，自然对流散热片的翅片间隙需要是稀疏的。如果翅片间隙足够大，沿翅片表面发展的边界层将不会重叠，从而产生最佳性能。由于翅片间隙是稀疏的，因此可以在间隙之间插入一个振荡片。它们可以产生气流并打破边界层以提高传热系数。所研究的九翅片散热器尺寸为80mm(长)* 80mm(宽)* 50mm(高)，翅片间隙为8mm。振荡片阵列的主要优点是没有轴承结构和体积变化小-它只增加了总散热器体积0.6%。此外，它的简单性使它成为一种高度可靠和低成本的设备。驱动电流可以是直流PWM或交流之间的3 V - 12 V，所以它是兼容大多数电子设备。根据冷却实验，垂直排列的阵列可以将测试散热器的热阻从3.41降低到1.61，消耗0.66 W。
{"title":"Heat transfer enhancement of a heat sink using electromagnetically-driven oscillating sheet array","authors":"H. Su, Ye Li","doi":"10.1109/ITHERM.2016.7517543","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517543","url":null,"abstract":"In this study, an oscillating sheet array device driven by electromagnetic force has been proposed. This device can be integrated with a heat sink to enhance heat transfer coefficient. Typically, the fin gaps of a heat sink for natural convection need to be sparse. If the fin gaps are large enough, the boundary layers that develop along the surface of the fins will not overlap and result in optimal performance. Since the fin gaps are sparse, it is allowed to insert an oscillating sheet between the gaps. They can produce airflow and break boundary layers to enhance heat transfer coefficient. The dimension of the heat sink under study with nine fins is 80 mm (L) * 80 mm (W) * 50 mm (H) and the fin gaps are 8 mm. The main advantages of the oscillating sheet array are no bearing structure and small volume change - it only increases the total heat sink volume by 0.6%. Moreover, its simplicity makes it a highly reliable and low cost device. The driving current can be either DC PWM or AC between 3 V - 12 V so it is compatible with most electronic devices. According to the cooling experiment, vertically arranged array can decrease the thermal resistance of the tested heat sink from 3.41 to 1.61 while consuming 0.66 W.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122812868","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517604
D. A. Moore, M. Slaby, T. Cader, K. Regimbal
The National Renewable Energy Laboratory (NREL) has implemented a state-of-the-art facility which tightly integrates campus and datacenter thermal management and allows for a chiller-less system with substantially lower capital and operating expenses than a traditional data center. To further lower these expenses, NREL recovers waste heat for use in climate control of offices and laboratories co-located with its data center. The NREL data center houses a liquid cooled High Performance Computing (HPC) system and supporting air cooled computing equipment collectively known as Peregrine. The energy efficiency of NREL's facility is explored using data acquired during facility operation. The facility achieved an average Power Usage Effectiveness (PUE) of 1.05 over the most recent year of operation. During the study, Peregrine had a peak power consumption of approximately 900kW, while the combination of the cooling towers, pumps, and lighting/plug loads consumed an average of 25.3 kW. Since the start of operations, NREL estimates that it saves approximately $200,000 per year through the recovery of datacenter waste heat. The availability of recovered heat allowed NREL to delay startup of the campus heating boiler by approximately one month during the autumn of 2015.
{"title":"Hybrid warm water cooled supercomputing system","authors":"D. A. Moore, M. Slaby, T. Cader, K. Regimbal","doi":"10.1109/ITHERM.2016.7517604","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517604","url":null,"abstract":"The National Renewable Energy Laboratory (NREL) has implemented a state-of-the-art facility which tightly integrates campus and datacenter thermal management and allows for a chiller-less system with substantially lower capital and operating expenses than a traditional data center. To further lower these expenses, NREL recovers waste heat for use in climate control of offices and laboratories co-located with its data center. The NREL data center houses a liquid cooled High Performance Computing (HPC) system and supporting air cooled computing equipment collectively known as Peregrine. The energy efficiency of NREL's facility is explored using data acquired during facility operation. The facility achieved an average Power Usage Effectiveness (PUE) of 1.05 over the most recent year of operation. During the study, Peregrine had a peak power consumption of approximately 900kW, while the combination of the cooling towers, pumps, and lighting/plug loads consumed an average of 25.3 kW. Since the start of operations, NREL estimates that it saves approximately $200,000 per year through the recovery of datacenter waste heat. The availability of recovered heat allowed NREL to delay startup of the campus heating boiler by approximately one month during the autumn of 2015.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"243 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115639953","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517589
K. Yazawa, D. Kendig, A. Shakouri, A. Ziabari, A. Shakouri
To achieve the required performance with high speed switching transistors, the gate feature length in communication devices is as small as a few tens of nanometers in multi finger configurations and transistors are arrayed in a Monolithic Microwave Integrated Circuit (MMIC). The technology therefore, makes thermal characterization more and more difficult. We employ a transient thermal imaging technique to characterize the surface temperature of such nano-featured circuits. The setup is for a non-invasive and indirect thermoreflectance method with external light illumination and CCD imaging. Due to the diffraction limit, that is set by the optical properties of the objective lens in the microscope, optical and thermal images of features smaller than 300 nm blur. We propose an algorithm to resolve this problem by using a Gaussian approximation for the diffraction function in order to blur the thermoreflectance map obtained from modeling, and further use it to reconstruct the true thermal map of sub-diffraction sized devices. Thermal expansion of the device under test is another challenge for such high magnification microscope imaging. We employ a three dimensional Piezo stage controller to take the pixel-by-pixel thermoreflectance coefficients. With this combination, thermal imaging for wires with one-pixel width ~100 nm is achieved. Transient thermal imaging of multi hotspots provides the information of thermal invasion to the neighboring circuit by the thermal diffusion from the hotspots in the MMIC. We will demonstrate the technology component, which combined, could gain the required information for a potential 3-D thermal structure analysis for practical multiple nano-featured hotspots on a chip.
{"title":"Thermal imaging of nanometer features","authors":"K. Yazawa, D. Kendig, A. Shakouri, A. Ziabari, A. Shakouri","doi":"10.1109/ITHERM.2016.7517589","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517589","url":null,"abstract":"To achieve the required performance with high speed switching transistors, the gate feature length in communication devices is as small as a few tens of nanometers in multi finger configurations and transistors are arrayed in a Monolithic Microwave Integrated Circuit (MMIC). The technology therefore, makes thermal characterization more and more difficult. We employ a transient thermal imaging technique to characterize the surface temperature of such nano-featured circuits. The setup is for a non-invasive and indirect thermoreflectance method with external light illumination and CCD imaging. Due to the diffraction limit, that is set by the optical properties of the objective lens in the microscope, optical and thermal images of features smaller than 300 nm blur. We propose an algorithm to resolve this problem by using a Gaussian approximation for the diffraction function in order to blur the thermoreflectance map obtained from modeling, and further use it to reconstruct the true thermal map of sub-diffraction sized devices. Thermal expansion of the device under test is another challenge for such high magnification microscope imaging. We employ a three dimensional Piezo stage controller to take the pixel-by-pixel thermoreflectance coefficients. With this combination, thermal imaging for wires with one-pixel width ~100 nm is achieved. Transient thermal imaging of multi hotspots provides the information of thermal invasion to the neighboring circuit by the thermal diffusion from the hotspots in the MMIC. We will demonstrate the technology component, which combined, could gain the required information for a potential 3-D thermal structure analysis for practical multiple nano-featured hotspots on a chip.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"68 7","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132624792","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517603
Cheng Chen, Run Hu, Xiaobing Luo
In this paper, a water-stirring radiator is presented, which possesses a sealed water chamber and a stirrer. Different from the conventional water-stirring radiators, there are no micro pump and connected channel in the present radiator, but the stirrer driven by a motor stirs water to cool the heat source. A set of experiments and FLUENT simulations were carried out to examine the performances, and a comparison between experimental and simulated values was presented.
{"title":"Experimental and numerical study of a water-stirring radiator","authors":"Cheng Chen, Run Hu, Xiaobing Luo","doi":"10.1109/ITHERM.2016.7517603","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517603","url":null,"abstract":"In this paper, a water-stirring radiator is presented, which possesses a sealed water chamber and a stirrer. Different from the conventional water-stirring radiators, there are no micro pump and connected channel in the present radiator, but the stirrer driven by a motor stirs water to cool the heat source. A set of experiments and FLUENT simulations were carried out to examine the performances, and a comparison between experimental and simulated values was presented.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131940925","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517637
P. Lall, YiHua Luo, L. Nguyen
Copper wire bonding is being increasingly used as an alternative to gold wire bonding in electronics packaging industry. Copper wire has advantages over gold wire including lower cost, higher electrical and thermal conductivity and also higher mechanical strength, making it a good alternative for the high power interconnection and fine pitch bonding applications. However, introduction of copper wire bonding has also created new sets of challenges including the high susceptibility of copper and Cu-Al intermetallic compound to oxidation. Wire bond reliability especially intermetallic cracking is a predominant failure mode resulting from thermal aging or temperature humidity exposure. In this paper, an IMC grain-level finite element model has been developed to simulate the interfacial de-bonding behavior in order to study the influence of the IMC microstructure characteristics on the mechanical reliability of Cu-Al wire bond. Voronoi tessellations have been used to construct both regular and irregular IMC grain shapes geometry. Intrinsic cohesive zone model has been adapted to model interactions between neighboring grain boundaries including the effect of uniform interfacial strength and Weibull distributed grain interfacial strength. Finally, Cu-Al IMC growth and phase transformation are modeled. Simulation results indicate Cu-Al IMC microstructure characteristics not only influence bond strength but also influences the crack initiation and propagation. Regular-shaped IMC grain provides Cu-Al wire bond with more bond strength while non-uniform grains reduce bond strength. Results also indicate that the increase of IMC thickness makes wire bond less reliable while the crack propagation mode changes with the phase transformation.
{"title":"De-bonding simulation of Cu-Al wire bond intermetallic compound layers","authors":"P. Lall, YiHua Luo, L. Nguyen","doi":"10.1109/ITHERM.2016.7517637","DOIUrl":"https://doi.org/10.1109/ITHERM.2016.7517637","url":null,"abstract":"Copper wire bonding is being increasingly used as an alternative to gold wire bonding in electronics packaging industry. Copper wire has advantages over gold wire including lower cost, higher electrical and thermal conductivity and also higher mechanical strength, making it a good alternative for the high power interconnection and fine pitch bonding applications. However, introduction of copper wire bonding has also created new sets of challenges including the high susceptibility of copper and Cu-Al intermetallic compound to oxidation. Wire bond reliability especially intermetallic cracking is a predominant failure mode resulting from thermal aging or temperature humidity exposure. In this paper, an IMC grain-level finite element model has been developed to simulate the interfacial de-bonding behavior in order to study the influence of the IMC microstructure characteristics on the mechanical reliability of Cu-Al wire bond. Voronoi tessellations have been used to construct both regular and irregular IMC grain shapes geometry. Intrinsic cohesive zone model has been adapted to model interactions between neighboring grain boundaries including the effect of uniform interfacial strength and Weibull distributed grain interfacial strength. Finally, Cu-Al IMC growth and phase transformation are modeled. Simulation results indicate Cu-Al IMC microstructure characteristics not only influence bond strength but also influences the crack initiation and propagation. Regular-shaped IMC grain provides Cu-Al wire bond with more bond strength while non-uniform grains reduce bond strength. Results also indicate that the increase of IMC thickness makes wire bond less reliable while the crack propagation mode changes with the phase transformation.","PeriodicalId":426908,"journal":{"name":"2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2016-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127537538","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 : 2016-05-01DOI: 10.1109/ITHERM.2016.7517721
Mohamed H. Nasr, C. Green, P. Kottke, Xuchen Zhang, Thomas E. Sarvey, Y. Joshi, M. Bakir, A. Fedorov
Performance of the next generation microprocessors is rapidly reaching its limits due to inability to remove heat, especially at high power density from so-called local “hotspots”. Convective boiling heat transfer in microgap heat sinks has the potential to dissipate ultra-high heat fluxes. We report results of an experimental investigation of heat transfer performance of three dedicated microgap coolers for hotspot thermal management. In this study, a rectangular microgap, batch micromachined in silicon and instrumented with thin-film resistive thermometry, is employed to assess its capability of dissipating extreme heat fluxes of multiple kW/cm2 while keeping the wall temperature within the limits dictated by electronics reliability. Convective boiling in microgap with heights of 5 μm and 10 μm was tested with and without pin fins in the microgap. The test section was heated from the bottom using resistive heaters and capped with glass to enable visual observation of two-phase flow regimes. Microgap pressure drop and wall temperature measurements, mapped into flow regimes, were obtained with R134a as the coolant, for heat fluxes up to 5 kW/cm2, mass fluxes up to 7,000 kg/m2s, at maximum pressures up to 1.5 MPa and outlet vapor qualities approaching unity. These experimental parameters constitute extreme values in terms of microgap height (smallest reported to our knowledge), mass fluxes, and heat fluxes. New flow regimes, including vapor plumes, liquid slugs, and ultra-thin wavy liquid film, were observed as a function of increasing heat flux and microgap geometry. Dominant mechanism(s) of two-phase heat transfer responsible for each regime have been postulated based on flow visualization correlated with pressure drop and thermal resistance measurements.
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