Pub Date : 2014-05-27DOI: 10.1109/ITHERM.2014.6892434
D. Demetriou, H. Erden, H. Khalifa, R. Schmidt
The transient behavior of IT equipment can be represented by a lumped thermal capacitance for use in data center level transient thermal simulations. Previous work has proposed a mathematical methodology to extract the necessary lumped capacitance parameters, the server's time constant and heat transfer effectiveness, via air temperature measurements. This work describes and experimentally tests that proposed methodology to introduce a possible approach for developing an easy-to-use database of lumped capacitance characteristics for use in transient thermal simulations. The database will allow the user to select the appropriate transient parameters based on characteristics that do not require an “autopsy” of each-and-every server in the data center. Experiments are conducted to provide representative transient parameters which classify the servers by mass density and operating air flow rate. The paper describes the experimental methodology in detail to allow for the easy addition of other IT equipment or future server generations.
{"title":"Development of an IT equipment lumped capacitance parameter database for transient data center simulations","authors":"D. Demetriou, H. Erden, H. Khalifa, R. Schmidt","doi":"10.1109/ITHERM.2014.6892434","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892434","url":null,"abstract":"The transient behavior of IT equipment can be represented by a lumped thermal capacitance for use in data center level transient thermal simulations. Previous work has proposed a mathematical methodology to extract the necessary lumped capacitance parameters, the server's time constant and heat transfer effectiveness, via air temperature measurements. This work describes and experimentally tests that proposed methodology to introduce a possible approach for developing an easy-to-use database of lumped capacitance characteristics for use in transient thermal simulations. The database will allow the user to select the appropriate transient parameters based on characteristics that do not require an “autopsy” of each-and-every server in the data center. Experiments are conducted to provide representative transient parameters which classify the servers by mass density and operating air flow rate. The paper describes the experimental methodology in detail to allow for the easy addition of other IT equipment or future server generations.","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"47 1","pages":"1330-1337"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86322617","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 : 2014-05-27DOI: 10.1109/ITHERM.2014.6892337
Kritika Upreti, Hung-Yun Lin, G. Subbarayan, D. Jung, B. Sammakia
Mechanical integrity of the dielectric stack is challenged by the trend towards porous, lower dielectric constant interlayer dielectric (ILD) materials. As a result, fracture in the ILD stacks caused either by assembly process or by the dicing process is an important reliability consideration. In general, there is a need to either assess the propensity of the structure to fracture under assembly conditions, or to design crack-arrest features that prevent propagation of cracks into active areas. In the case of wire bonded packages, the reliability concern associated with the fracture of Ultra Low-k (ULK) dielectrics while bonding over the active circuits (BOAC) is a significant challenge due to the impact load and the high ultrasonic energy transmitted to the ILD stack. In this paper, a multi-level modeling procedure is presented to assess the risk of fracture in ILD stacks during wire bonding process. First, a nonlinear, dynamic finite element model is developed to simulate the process steps - impact stage and last cycle of ultrasonic vibration and study the mechanical response of the ball, pad, and the underlying ULK under pad during copper wire bonding. Further, a simulation framework based on enriched isogeometric approximations is presented to compute damage accumulation in the ULK stacks using a cohesive damage description. The simulation framework is employed to develop insights on the potential crack initiation sites within the ILD stack and to evaluate the risk of fracture during each process step.
{"title":"Simulations of damage and fracture in ULK under pad structures during Cu wirebond process","authors":"Kritika Upreti, Hung-Yun Lin, G. Subbarayan, D. Jung, B. Sammakia","doi":"10.1109/ITHERM.2014.6892337","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892337","url":null,"abstract":"Mechanical integrity of the dielectric stack is challenged by the trend towards porous, lower dielectric constant interlayer dielectric (ILD) materials. As a result, fracture in the ILD stacks caused either by assembly process or by the dicing process is an important reliability consideration. In general, there is a need to either assess the propensity of the structure to fracture under assembly conditions, or to design crack-arrest features that prevent propagation of cracks into active areas. In the case of wire bonded packages, the reliability concern associated with the fracture of Ultra Low-k (ULK) dielectrics while bonding over the active circuits (BOAC) is a significant challenge due to the impact load and the high ultrasonic energy transmitted to the ILD stack. In this paper, a multi-level modeling procedure is presented to assess the risk of fracture in ILD stacks during wire bonding process. First, a nonlinear, dynamic finite element model is developed to simulate the process steps - impact stage and last cycle of ultrasonic vibration and study the mechanical response of the ball, pad, and the underlying ULK under pad during copper wire bonding. Further, a simulation framework based on enriched isogeometric approximations is presented to compute damage accumulation in the ULK stacks using a cohesive damage description. The simulation framework is employed to develop insights on the potential crack initiation sites within the ILD stack and to evaluate the risk of fracture during each process step.","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"63 11","pages":"609-615"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91514664","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 : 2014-05-27DOI: 10.1109/ITHERM.2014.6892272
Munshi M. Basit, M. Motalab, J. Suhling, P. Lall
Lead free solder materials are widely used in electronic packaging industry due to environmental concerns. However, experimental testing and microstructural characterization have revealed that Pb-free solders exhibit evolving properties that change significantly with environmental exposures such as isothermal aging and thermal cycling. These changes are especially large in harsh environments, where the effects of aging on solder joint behavior must be accounted for and included in constitutive models when predicting reliability. In this work, we have adapted the Anand viscoplastic stress-strain relations for Pb-free solders to include material parameters that evolve with the thermal history of the solder material. In particular, aging effects have been examined by performing uniaxial tensile tests on SAC305 samples that were aged for various durations (0-12 months) at temperature of 100 C. For each set of aging conditions, several sets of constant strain rate and temperature tests were conducted on the aged solder samples. Testing conditions included strain rates of 0.001, 0.0001, and 0.00001 (1/sec), and temperatures of 25, 50, 75, 100, and 125 C. Using the measured uniaxial test data, the Anand parameters were calculated for each set of aging conditions, and the effects of aging on the nine Anand model parameters were determined. Mechanical tests have been performed using both water quenched (WQ) and reflowed (RF) SAC305 samples (two unique specimen microstructures). In the case of the water quenched samples, there is rapid microstructural transitioning during the brief time that occurs between placing molten solder into the glass tubes and immersing the tubes in water bath. On the other hand, the reflowed samples are first cooled by water quenching, and then sent through a reflow oven to re-melt the solder in the tubes and subject them to a desired temperature profile matching that used in PCB assembly. From the experimental results, the differences between the extracted Anand model parameters of water quenched and reflowed samples were high for samples with no prior aging. As expected, the water quenched samples had much higher mechanical properties (stiffness and strength) than reflowed samples prior to aging. For both the water quenched and reflowed specimens, significant degradation of the mechanical properties was observed with aging. The variations of the Anand model parameters with aging time have been characterized, and empirical relationships were established to model the observed changes. After long aging times, the water quenched and reflowed SAC305 materials were found to exhibit similar mechanical properties, and thus their Anand parameters converged and became nearly identical.
{"title":"The effects of aging on the Anand viscoplastic constitutive model for SAC305 solder","authors":"Munshi M. Basit, M. Motalab, J. Suhling, P. Lall","doi":"10.1109/ITHERM.2014.6892272","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892272","url":null,"abstract":"Lead free solder materials are widely used in electronic packaging industry due to environmental concerns. However, experimental testing and microstructural characterization have revealed that Pb-free solders exhibit evolving properties that change significantly with environmental exposures such as isothermal aging and thermal cycling. These changes are especially large in harsh environments, where the effects of aging on solder joint behavior must be accounted for and included in constitutive models when predicting reliability. In this work, we have adapted the Anand viscoplastic stress-strain relations for Pb-free solders to include material parameters that evolve with the thermal history of the solder material. In particular, aging effects have been examined by performing uniaxial tensile tests on SAC305 samples that were aged for various durations (0-12 months) at temperature of 100 C. For each set of aging conditions, several sets of constant strain rate and temperature tests were conducted on the aged solder samples. Testing conditions included strain rates of 0.001, 0.0001, and 0.00001 (1/sec), and temperatures of 25, 50, 75, 100, and 125 C. Using the measured uniaxial test data, the Anand parameters were calculated for each set of aging conditions, and the effects of aging on the nine Anand model parameters were determined. Mechanical tests have been performed using both water quenched (WQ) and reflowed (RF) SAC305 samples (two unique specimen microstructures). In the case of the water quenched samples, there is rapid microstructural transitioning during the brief time that occurs between placing molten solder into the glass tubes and immersing the tubes in water bath. On the other hand, the reflowed samples are first cooled by water quenching, and then sent through a reflow oven to re-melt the solder in the tubes and subject them to a desired temperature profile matching that used in PCB assembly. From the experimental results, the differences between the extracted Anand model parameters of water quenched and reflowed samples were high for samples with no prior aging. As expected, the water quenched samples had much higher mechanical properties (stiffness and strength) than reflowed samples prior to aging. For both the water quenched and reflowed specimens, significant degradation of the mechanical properties was observed with aging. The variations of the Anand model parameters with aging time have been characterized, and empirical relationships were established to model the observed changes. After long aging times, the water quenched and reflowed SAC305 materials were found to exhibit similar mechanical properties, and thus their Anand parameters converged and became nearly identical.","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"35 1","pages":"112-126"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90206776","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 : 2014-05-27DOI: 10.1109/ITHERM.2014.6892349
M. del Valle, A. Ortega
Hybrid air/liquid cooling systems used in data centers enable localized, on-demand cooling, or “smart cooling” using various approaches such as rear door heat exchangers, overhead cooling systems and in row cooling systems. These systems offer the potential to achieve higher energy efficiency by providing local cooling only when it is needed, thereby reducing the overprovisioning that is endemic to traditional systems. At the heart of all hybrid cooling systems is an air to liquid cross flow heat exchanger which regulates the amount of cooling that the system provides by modulating the liquid or air flows or temperatures. Understanding the transient response of the heat exchanger is crucial for the precise control of the system. The aim of this work is the development of a rear door heat exchanger compact model using Artificial Neural Networks (ANN). The transient behavior of the heat exchanger is studied using a Finite Difference (FD) model. Different temperatures perturbations are introduced in the heat exchanger model to study its transient response. The finite different results are then used to train an ANN compact model. Both models are compared in terms of accuracy and computational resources.
{"title":"Numerical and compact models to predict the transient behavior of cross-flow heat exchangers in data center applications","authors":"M. del Valle, A. Ortega","doi":"10.1109/ITHERM.2014.6892349","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892349","url":null,"abstract":"Hybrid air/liquid cooling systems used in data centers enable localized, on-demand cooling, or “smart cooling” using various approaches such as rear door heat exchangers, overhead cooling systems and in row cooling systems. These systems offer the potential to achieve higher energy efficiency by providing local cooling only when it is needed, thereby reducing the overprovisioning that is endemic to traditional systems. At the heart of all hybrid cooling systems is an air to liquid cross flow heat exchanger which regulates the amount of cooling that the system provides by modulating the liquid or air flows or temperatures. Understanding the transient response of the heat exchanger is crucial for the precise control of the system. The aim of this work is the development of a rear door heat exchanger compact model using Artificial Neural Networks (ANN). The transient behavior of the heat exchanger is studied using a Finite Difference (FD) model. Different temperatures perturbations are introduced in the heat exchanger model to study its transient response. The finite different results are then used to train an ANN compact model. Both models are compared in terms of accuracy and computational resources.","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"30 1","pages":"698-705"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83105558","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 : 2014-05-27DOI: 10.1109/ITHERM.2014.6892416
D. Altman, M. Tyhach, J. Mcclymonds, Samuel H. Kim, S. Graham, Jungwan Cho, K. Goodson, D. Francis, F. Faili, F. Ejeckam, S. Bernstein
The emergence of Gallium Nitride-based High Electron Mobility Transistor (HEMT) technology has proven to be a significant enabler of next generation RF systems. However, thermal considerations currently prevent exploitation of the full electromagnetic potential of GaN in most applications, limiting HEMT areal power density (W/mm2) to a small fraction of electrically limited performance. GaN on Diamond technology has been developed to reduce near junction thermal resistance in GaN HEMTs. However, optimal implementation of GaN on Diamond requires thorough understanding of thermal transport in GaN, CVD diamond and interfacial layers in GaN on Diamond substrates, which has not been thoroughly previously addressed. To meet this need, our study pursued characterization of constituent thermal properties in GaN on Diamond substrates and temperature measurement of operational GaN on Diamond HEMTs, employing electro-thermal modeling of the HEMT devices to interpret and relate data. Strong agreement was obtained between simulations and HEMT operational temperature measurements made using two independent thermal metrology techniques, enabling confident assessment of peak junction temperature. The results support the potential of GaN on Diamond to enable a 3X increase in HEMT areal dissipation density without significantly increasing operational temperature. Such increases in HEMT power density will enable smaller, higher power density Monolithic Microwave Integrated Circuits (MMICs).
{"title":"Analysis and characterization of thermal transport in GaN HEMTs on Diamond substrates","authors":"D. Altman, M. Tyhach, J. Mcclymonds, Samuel H. Kim, S. Graham, Jungwan Cho, K. Goodson, D. Francis, F. Faili, F. Ejeckam, S. Bernstein","doi":"10.1109/ITHERM.2014.6892416","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892416","url":null,"abstract":"The emergence of Gallium Nitride-based High Electron Mobility Transistor (HEMT) technology has proven to be a significant enabler of next generation RF systems. However, thermal considerations currently prevent exploitation of the full electromagnetic potential of GaN in most applications, limiting HEMT areal power density (W/mm2) to a small fraction of electrically limited performance. GaN on Diamond technology has been developed to reduce near junction thermal resistance in GaN HEMTs. However, optimal implementation of GaN on Diamond requires thorough understanding of thermal transport in GaN, CVD diamond and interfacial layers in GaN on Diamond substrates, which has not been thoroughly previously addressed. To meet this need, our study pursued characterization of constituent thermal properties in GaN on Diamond substrates and temperature measurement of operational GaN on Diamond HEMTs, employing electro-thermal modeling of the HEMT devices to interpret and relate data. Strong agreement was obtained between simulations and HEMT operational temperature measurements made using two independent thermal metrology techniques, enabling confident assessment of peak junction temperature. The results support the potential of GaN on Diamond to enable a 3X increase in HEMT areal dissipation density without significantly increasing operational temperature. Such increases in HEMT power density will enable smaller, higher power density Monolithic Microwave Integrated Circuits (MMICs).","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"79 1","pages":"1199-1205"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81391750","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 : 2014-05-27DOI: 10.1109/ITHERM.2014.6892382
I. Sauciuc, S. Goyal, M. Pei, T. Harirchian, Maritza Tse, R. Kwasnick, S. Tripathi, A. Matusevich
The traditional approach of thermo-mechanical (T-M) reliability modeling is based on power cycle events. This approach is not useful for products which are rarely powered down, because power cycles alone do not capture all the reliability stress from temperature variation over these products' use life. This paper describes a methodology to determine the temperature cycle requirements for products like smartphones and tablets which accounts for the temperature variation associated with usage events, which we call “mini-cycles”. The T-M model is based on the distribution of individual users' histories as a series of events over time, which is then translated into a temperature vs. time trace for each user. These temperature traces are then used as the main inputs to T-M models, for example using the Norris-Landzberg (N-L) acceleration model to evaluate solder damage for each user. Results are summarized in a distribution of T-M damage across all users. This new methodology improves the understanding of thermo-mechanical reliability requirements due to the impact of “mini-cycles”.
{"title":"Event-based use conditions method for thermo-mechanical reliability risk assessment","authors":"I. Sauciuc, S. Goyal, M. Pei, T. Harirchian, Maritza Tse, R. Kwasnick, S. Tripathi, A. Matusevich","doi":"10.1109/ITHERM.2014.6892382","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892382","url":null,"abstract":"The traditional approach of thermo-mechanical (T-M) reliability modeling is based on power cycle events. This approach is not useful for products which are rarely powered down, because power cycles alone do not capture all the reliability stress from temperature variation over these products' use life. This paper describes a methodology to determine the temperature cycle requirements for products like smartphones and tablets which accounts for the temperature variation associated with usage events, which we call “mini-cycles”. The T-M model is based on the distribution of individual users' histories as a series of events over time, which is then translated into a temperature vs. time trace for each user. These temperature traces are then used as the main inputs to T-M models, for example using the Norris-Landzberg (N-L) acceleration model to evaluate solder damage for each user. Results are summarized in a distribution of T-M damage across all users. This new methodology improves the understanding of thermo-mechanical reliability requirements due to the impact of “mini-cycles”.","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"8 1","pages":"937-941"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81470545","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 : 2014-05-27DOI: 10.1109/ITHERM.2014.6892275
M. Hasnine, J. Suhling, B. Prorok, M. Bozack, P. Lall
In this work, aging phenomena in solder joints have been explored by nano-mechanical testing. Using nanoindentation techniques, the elastic, plastic, and creep behavior of SAC305 solder joint materials have been explored for various aging conditions. Single crystal solder joints were first extracted from PBGA assemblies (14 × 14 mm, 0.8 mm ball pitch, 0.46 mm ball diameter), and then subjected to aging at T = 125 C for various aging times. After the aging exposures, the joints were loaded in the nano-indentor, and the load-deformation behavior during indentation was used to characterize the mechanical properties of the solder joints for various aging conditions including modulus, hardness, and yield stress. Using constant force at max indentation, the creep response of the aged and non-aged solder joint materials have also been measured for various stress levels. With this approach, aging effects have been quantified in joints, and their magnitudes correlated to those observed in testing of miniature bulk specimens. The measured results have demonstrated that the mechanical behavior of actual solder joints degrade significantly with aging. The results show that the aging induced degradations of the mechanical properties (modulus, hardness) in the SAC joints were of similar order (30-40%) as those seen previously in the testing of larger “bulk” uniaxial solder specimens. The creep rate of the tested SAC305 joints were found to increase by up to 75X with one year of aging. These degradations, while significant, were much less than those observed in larger bulk solder uniaxial tensile specimens with several hundred grains, where the increase was over 900X. Additional testing has been performed on very small tensile specimens with approximately 10 grains, and the aging-induced creep rate degradations found in these specimens were on the same order of magnitude as those observed in the single grain joints. Thus, the lack of the grain boundary sliding creep mechanism in the single grain joints is an important factor in avoiding the extremely large creep rate degradations ocurring in larger bulk SAC samples. The test results also show that the elastic, plastic, and creep properties of the solder joints and their sensitivities to aging are highly dependent on their crystal orientations. Polarized light microscopy and Electron Back Scattered Diffraction (EBSD) were used to identify the grain structure and crystal orientations in the tested joints. Microstructural analysis of the joints has shown that Ag3Sn precipitates coarsen during isothermal aging, which results in fewer but larger particles. The Sn dendrite cell size also was observed to grow significantly, but the boundaries are no longer well defined due to coarsening.
本文采用纳米力学测试的方法研究了焊点的老化现象。利用纳米压痕技术，研究了SAC305焊点材料在不同时效条件下的弹性、塑性和蠕变行为。首先从PBGA组件(14 × 14 mm, 0.8 mm球距，0.46 mm球径)中提取单晶焊点，然后在T = 125℃下进行不同时效时间的时效处理。老化后，将焊点加载到纳米压痕器中，并利用压痕过程中的载荷变形行为来表征不同老化条件下焊点的力学性能，包括模量、硬度和屈服应力。在最大压痕处使用恒定力，还测量了不同应力水平下时效和非时效焊点材料的蠕变响应。利用这种方法，对关节的老化效应进行了量化，并将其大小与微型体试件试验中观察到的结果相关联。测试结果表明，实际焊点的力学性能随着老化而显著下降。结果表明，SAC接头的力学性能(模量、硬度)的时效退化与之前在较大的“大块”单轴焊料试样中观察到的相似(30-40%)。经测试的SAC305接头的蠕变率在时效1年后提高了75倍。这些退化虽然显著，但远远小于在具有数百晶粒的较大块体单轴拉伸试样中观察到的，其中增加超过900X。在大约有10个晶粒的非常小的拉伸试样上进行了额外的测试，在这些试样中发现的时效引起的蠕变速率下降与在单晶粒节理中观察到的相同数量级。因此，在单晶粒节理中缺乏晶界滑动蠕变机制是避免较大体积SAC试样发生极大蠕变速率退化的重要因素。试验结果还表明，焊点的弹性、塑性和蠕变性能及其对时效的敏感性与晶体取向高度相关。利用偏振光显微镜和电子背散射衍射(EBSD)对接头的晶粒结构和晶体取向进行了表征。对接头的组织分析表明，等温时效过程中，Ag3Sn析出粗晶，晶粒数量少但体积大。锡树突细胞的大小也明显增大，但由于粗化，边界不再明确。
{"title":"Nanomechanical characterization of SAC305 solder joints - effects of aging","authors":"M. Hasnine, J. Suhling, B. Prorok, M. Bozack, P. Lall","doi":"10.1109/ITHERM.2014.6892275","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892275","url":null,"abstract":"In this work, aging phenomena in solder joints have been explored by nano-mechanical testing. Using nanoindentation techniques, the elastic, plastic, and creep behavior of SAC305 solder joint materials have been explored for various aging conditions. Single crystal solder joints were first extracted from PBGA assemblies (14 × 14 mm, 0.8 mm ball pitch, 0.46 mm ball diameter), and then subjected to aging at T = 125 C for various aging times. After the aging exposures, the joints were loaded in the nano-indentor, and the load-deformation behavior during indentation was used to characterize the mechanical properties of the solder joints for various aging conditions including modulus, hardness, and yield stress. Using constant force at max indentation, the creep response of the aged and non-aged solder joint materials have also been measured for various stress levels. With this approach, aging effects have been quantified in joints, and their magnitudes correlated to those observed in testing of miniature bulk specimens. The measured results have demonstrated that the mechanical behavior of actual solder joints degrade significantly with aging. The results show that the aging induced degradations of the mechanical properties (modulus, hardness) in the SAC joints were of similar order (30-40%) as those seen previously in the testing of larger “bulk” uniaxial solder specimens. The creep rate of the tested SAC305 joints were found to increase by up to 75X with one year of aging. These degradations, while significant, were much less than those observed in larger bulk solder uniaxial tensile specimens with several hundred grains, where the increase was over 900X. Additional testing has been performed on very small tensile specimens with approximately 10 grains, and the aging-induced creep rate degradations found in these specimens were on the same order of magnitude as those observed in the single grain joints. Thus, the lack of the grain boundary sliding creep mechanism in the single grain joints is an important factor in avoiding the extremely large creep rate degradations ocurring in larger bulk SAC samples. The test results also show that the elastic, plastic, and creep properties of the solder joints and their sensitivities to aging are highly dependent on their crystal orientations. Polarized light microscopy and Electron Back Scattered Diffraction (EBSD) were used to identify the grain structure and crystal orientations in the tested joints. Microstructural analysis of the joints has shown that Ag3Sn precipitates coarsen during isothermal aging, which results in fewer but larger particles. The Sn dendrite cell size also was observed to grow significantly, but the boundaries are no longer well defined due to coarsening.","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"8 Pt 2 1","pages":"152-160"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83976968","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 : 2014-05-27DOI: 10.1109/ITHERM.2014.6892334
G. Goth, Robert K. Mullady, R. Zoodsma, A. VanDeventer, D. Porter, P. Kelly
On September 19, 2012 IBM announced its latest System z Enterprise Class zServer, the IBM zEnterprise EC12 (zEC12). This server uses a 96 mm glass ceramic substrate to interconnect processors and related cache chips on a multi-chip module (MCM). In rare applications, the power in these MCMs can exceed 2000W, well beyond air cooling capability. This paper describes a new cooling methodology IBM employs in zEC12 to cool its processor MCMs. From the IBM S/390 G4, which first shipped in 1997, through z196 which is EC12's enterprise class predecessor, IBM's high end System z servers have utilized vapor compression refrigeration to cool its processor MCMs. In zEC12, the thermal solution employs an air to water heat exchanger to provide this function. This paper discusses the technical details of this cooling system. Thermal performance of each component of the cooling path from processor core to ambient, as well as comparison to prior cooling approaches in terms of temperatures, reliability, and energy efficiency will be reviewed. In summary, this technology shows considerable promise for cooling this class of server.
2012年9月19日，IBM宣布了其最新的System z企业级zServer, IBM zEnterprise EC12 (zEC12)。该服务器采用96毫米玻璃陶瓷衬底，将处理器和相关缓存芯片连接在一个多芯片模块(MCM)上。在一些罕见的应用中，这些mcm的功率可以超过2000W，远远超出了空气冷却能力。本文描述了IBM在zEC12中采用的一种新的冷却方法来冷却其处理器mcm。从1997年首次发货的IBM S/390 G4到EC12的企业级前身z196, IBM的高端System z服务器已经利用蒸汽压缩制冷来冷却其处理器mcm。在zEC12中，热解决方案采用空气-水热交换器来提供此功能。本文讨论了该冷却系统的技术细节。从处理器核心到环境冷却路径的每个组件的热性能，以及在温度，可靠性和能源效率方面与先前的冷却方法的比较将被审查。总之，这项技术在冷却这类服务器方面显示出相当大的前景。
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Pub Date : 2014-05-27DOI: 10.1109/ITHERM.2014.6892408
D. Hackenberg
Data centers are very costly structures, both in terms of capital and operational expenditures. The high innovation rate in the IT business conflicts with the long-term character of data centers. In order to ensure lifetime usability, flexibility is a major concern for any data center design. Recent developments of data center air-cooling, in particular containment solutions for hot/cold air separation, allow rethinking of traditional data center design approaches. In this paper we present the Plenum concept that represents a major overhaul of traditional design principles. Our approach requires the construction of a full additional building story instead of a traditional raised floor. We then position the computer room air-handling (CRAH) units directly below the hot aisle of a block of racks. The down- ward flow direction of hot air makes the strict use of hot/cold air separation mandatory. Our approach minimizes or eliminates support space on the IT floor, moves almost all support structures into the Plenum, and creates very clean interfaces between both spaces. This greatly reduces the need for support personnel on the IT floor. Vice versa, IT personnel does not need to access support spaces, allowing for simplified data center operations. Insight from the planning process of a 5 MW data center currently under construction at TU Dresden shows that the construction of a full building story below the IT floor instead of a traditional raised floor does not necessarily increase the building volume. The simplified access and the separation of IT and support personnel reduces corridor and access spaces. We show that the overall building volume can even be decreased in comparison to classical approaches. Our design easily supports more than 15 kW average heat loads per rack with n+1 CRAH unit redundancy at a highly efficient CRAH operating point and with little scalability limitations regarding computer room size.
{"title":"The Plenum concept: Improving scalability, security, and efficiency for data centers","authors":"D. Hackenberg","doi":"10.1109/ITHERM.2014.6892408","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892408","url":null,"abstract":"Data centers are very costly structures, both in terms of capital and operational expenditures. The high innovation rate in the IT business conflicts with the long-term character of data centers. In order to ensure lifetime usability, flexibility is a major concern for any data center design. Recent developments of data center air-cooling, in particular containment solutions for hot/cold air separation, allow rethinking of traditional data center design approaches. In this paper we present the Plenum concept that represents a major overhaul of traditional design principles. Our approach requires the construction of a full additional building story instead of a traditional raised floor. We then position the computer room air-handling (CRAH) units directly below the hot aisle of a block of racks. The down- ward flow direction of hot air makes the strict use of hot/cold air separation mandatory. Our approach minimizes or eliminates support space on the IT floor, moves almost all support structures into the Plenum, and creates very clean interfaces between both spaces. This greatly reduces the need for support personnel on the IT floor. Vice versa, IT personnel does not need to access support spaces, allowing for simplified data center operations. Insight from the planning process of a 5 MW data center currently under construction at TU Dresden shows that the construction of a full building story below the IT floor instead of a traditional raised floor does not necessarily increase the building volume. The simplified access and the separation of IT and support personnel reduces corridor and access spaces. We show that the overall building volume can even be decreased in comparison to classical approaches. Our design easily supports more than 15 kW average heat loads per rack with n+1 CRAH unit redundancy at a highly efficient CRAH operating point and with little scalability limitations regarding computer room size.","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"18 1","pages":"1137-1144"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78033531","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 : 2014-05-27DOI: 10.1109/ITHERM.2014.6892303
Sai Sudharsanan Paranjothy, Y. Singh, Allen Tippman, Hung-Yun Lin, G. Subbarayan, D. Jung, B. Sammakia
In recent years, there is increasing interest in copper wirebond technology as an alternative to gold wirebond in microelectronic devices due to its superior electrical performance and low cost. At present, validated constitutive models for the strain rate and temperature dependent behavior of Cu free air ball (FAB) appear to be largely missing in the literature. The lack of reliable constitutive models for the Cu FAB has hampered the modeling of the wirebonding process and the ability to assess risk of fracture in ultra low-k dielectric stacks. The challenge to FAB characterization is primarily due to the difficulty in performing mechanical tests on spherical FAB of micrometers in size. To address this challenge, we perform compression tests on FAB using custom-built microscale tester in the current study. Specifically, the tester has three closed-loop controlled linear stages with submicron resolutions, a manual tilt stage, a six-axis load cell with sub-Newton load resolution for eliminating misalignment, a milliNewton resolution load cell, a capacitance sensor to estimate sample deformation and to control the vertical stage in closed loop, a high working depth camera for viewing the sample deformation, and controllers for the stages implemented in the LabVIEW environment. We compress the FAB between tungsten carbide punches and develop a constitutive model for the copper of FAB through an inverse modeling procedure. In the inverse procedure, the assumed constitutive model parameter values are iterated until the load-displacement response matches the experimentally observed response.
{"title":"Characterization of cu free air ball constitutive behavior using microscale compression test","authors":"Sai Sudharsanan Paranjothy, Y. Singh, Allen Tippman, Hung-Yun Lin, G. Subbarayan, D. Jung, B. Sammakia","doi":"10.1109/ITHERM.2014.6892303","DOIUrl":"https://doi.org/10.1109/ITHERM.2014.6892303","url":null,"abstract":"In recent years, there is increasing interest in copper wirebond technology as an alternative to gold wirebond in microelectronic devices due to its superior electrical performance and low cost. At present, validated constitutive models for the strain rate and temperature dependent behavior of Cu free air ball (FAB) appear to be largely missing in the literature. The lack of reliable constitutive models for the Cu FAB has hampered the modeling of the wirebonding process and the ability to assess risk of fracture in ultra low-k dielectric stacks. The challenge to FAB characterization is primarily due to the difficulty in performing mechanical tests on spherical FAB of micrometers in size. To address this challenge, we perform compression tests on FAB using custom-built microscale tester in the current study. Specifically, the tester has three closed-loop controlled linear stages with submicron resolutions, a manual tilt stage, a six-axis load cell with sub-Newton load resolution for eliminating misalignment, a milliNewton resolution load cell, a capacitance sensor to estimate sample deformation and to control the vertical stage in closed loop, a high working depth camera for viewing the sample deformation, and controllers for the stages implemented in the LabVIEW environment. We compress the FAB between tungsten carbide punches and develop a constitutive model for the copper of FAB through an inverse modeling procedure. In the inverse procedure, the assumed constitutive model parameter values are iterated until the load-displacement response matches the experimentally observed response.","PeriodicalId":12453,"journal":{"name":"Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm)","volume":"55 1","pages":"365-368"},"PeriodicalIF":0.0,"publicationDate":"2014-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73380354","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}
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