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Artigos de revistas sobre o assunto "RF stress and thermic cycling"
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Hartner, Walter, Martin Niessner, Francesca Arcioni, Markus Fink, Christian Geissler, Birgit Hebler, Gerhard Haubner e Maciej Wojnowski. "Reliability and Performance of Wafer Level Fan Out Package for Automotive Radar". Journal of Surface Mount Technology 34, n.º 1 (6 de abril de 2021): 32–39. http://dx.doi.org/10.37665/smt.v34i1.12.
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Embedded wafer level ball grid array (eWLB) or FO-WLP (Fan-out wafer-level packaging) is investigated as a package for MMICs (Monolithic Microwave Integrated Circuit) for automotive radar applications in the 77GHz range. Special focus is put on the thermo-mechanical performance to achieve automotive quality targets. The typical fatigue modes “solder ball fatigue” and “copper fatigue”, evolving during thermo-mechanical stress like cycling on board will be discussed. Simulation as well as experimental preparation results for typical fatigue levels are given. In addition, several influencing parameters are listed and rated regarding their effectiveness. The theoretical framework why solder ball fatigue is the only failure mode causing electrical failure is provided.
The impact of different thermo-mechanically driven fatigue modes is discussed. The two important parameters to be considered for the functionality of the Radar system are RF (Radio Frequency) and thermal performance.
For elaborating the RF performance with present fatigue modes, the phase shift between different channels and pads is analyzed by full-wave EM (Electromagnetic) simulation. It is found that for fatigue levels up to 90% the phase shift stays below specification for single fatigue modes and may approach specification only for an unlikely combination of all 90% fatigue modes.
For assessing the thermal performance with present fatigue modes, thermal simulation as well as thermal measurements are used. Assuming 50% degradation in average for all thermal balls, an increase in RTH of up to about 30% is seen. On average for all thermal measurements, the deviation between measurement and simulation is within ±1°C.
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Putaala, Jussi, Olli Salmela, Olli Nousiainen, Tero Kangasvieri, Jouko Vähäkangas, Antti Uusimäki e Jyrki Lappalainen. "Lifetime prediction and design aspects of reliable lead-free non-collapsible BGA joints in LTCC packages for RF/microwave telecommunication applications". Soldering & Surface Mount Technology 26, n.º 3 (27 de maio de 2014): 117–28. http://dx.doi.org/10.1108/ssmt-07-2013-0018.
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Purpose – The purpose of this paper is to describe the behavior of different lead-free solders (95.5Sn3.8Ag0.7Cu, i.e. SAC387 and Sn7In4.1Ag0.5Cu, i.e. SAC-In) in thermomechanically loaded non-collapsible ball grid array (BGA) joints of a low-temperature co-fired ceramic (LTCC) module. The validity of a modified Engelmaier’s model was tested to verify its capability to predict the characteristic lifetime of an LTCC module assembly implementable in field applications. Design/methodology/approach – Five printed wiring board (PWB) assemblies, each carrying eight LTCC modules, were fabricated and exposed to a temperature cycling test over a −40 to 125°C temperature range to determine the characteristic lifetimes of interconnections in the LTCC module/PWB assemblies. The failure mechanisms of the test assemblies were verified using scanning acoustic microscopy, scanning electron microscopy (SEM) and field emission SEM investigation. A stress-dependent Engelmaier’s model, adjusted for plastic-core solder ball (PCSB) BGA structures, was used to predict the characteristic lifetimes of the assemblies. Findings – Depending on the joint configuration, characteristic lifetimes of up to 1,920 cycles were achieved in the thermal cycling testing. The results showed that intergranular (creep) failures occurred primarily only in the joints containing Sn7In4.1Ag0.5Cu solder. Other primary failure mechanisms (mixed transgranular/intergranular, separation of the intermetallic compound/solder interface and cracking in the interface between the ceramic and metallization) were observed in the other joint configurations. The modified Engelmaier’s model was found to predict the lifetime of interconnections with good accuracy. The results confirmed the superiority of SAC-In solder over SAC in terms of reliability, and also proved that an air cavity structure of the module, which enhances its radio frequency (RF) performance, did not degrade the reliability of the second-level interconnections of the test assemblies. Originality/value – This paper shows the superiority of SAC-In solder over SAC387 solder in terms of reliability and verifies the applicability of the modified Engelmaier’s model as an accurate lifetime prediction method for PCSB BGA structures for the presented LTCC packages for RF/microwave telecommunication applications.
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Kumbhat, Nitesh, Fuhan Liu, Venky Sundaram, Vivek Sridharan, Abhishek Choudhury, Hunter Chan e Rao Tummala. "Chip-last Embedded Actives and Passives in Ultra-Miniaturized Organic Packages with Chip-First Benefits". International Symposium on Microelectronics 2010, n.º 1 (1 de janeiro de 2010): 000537–42. http://dx.doi.org/10.4071/isom-2010-wp1-paper1.
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Embedded actives and passives are being pursued by chip-first and wafer-level fan-out approaches to address high functionality and miniaturization. A next generation embedding alternative- “chip-last embedding”, which retains all the benefits of chip-first, has been demonstrated at Georgia Tech for complex multi-component heterogeneous systems. This paper presents detailed results from the first demonstration of this novel technology called Embedded MEMS, Actives and Passives (EMAP) with Chip-Last (CL) interconnections. This technology is targeted at highly integrated modules and systems with multiple 2D and 3D ICs for RF, Digital, Analog, MEMS and passive devices. Ultra-thin (55μm) silicon test dies were embedded in a 60μm deep cavity within 6-metal layer substrates yielding a total module thickness of 0.22mm. The robustness of substrate materials and processes was demonstrated using thermal cycling of the blind-vias and through-holes. The embedded IC was bonded to the substrate at 160°C by ultra-fine pitch (30–50μm) and low-profile (10–15μm) Cu-to-Cu interconnections with polymer adhesives. Two different die-sizes 3mm × 3mm and 7mm × 7mm were investigated for reliability performance of these interconnections, which passed 1000 thermal cycles, in addition to Highly Accelerated Stress Test (HAST) and High Temperature Storage Test (HTS). Comprehensive analysis of new materials and processes used in the chip-last embedding technology has been carried out demonstrating the advantages and robustness of this promising technology. Due to manufacturing process simplicity and unparalleled set of benefits, the chip-last technology provides the benefits of chip-first while enabling highly miniaturized, multi-band, high performance modules with embedded actives and passives.
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Razzaghi, Mohammadreza, Afsar Asghari-azghan, Saeed Montazeri, Zahra Razzaghi, Mohammad Mohsen Mazloomfard e Reza Vafaee. "Intravaginal Pulsed Contractile Radiofrequency for Stress Urinary Incontinence Treatment; A Safety Study". Journal of Lasers in Medical Sciences 12, n.º 1 (9 de outubro de 2021): e56-e56. http://dx.doi.org/10.34172/jlms.2021.56.
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Introduction: Radiofrequency (RF)-based stress urinary incontinence (SUI) treatment, which has quickly attracted attention, is administered in an office setting. This pilot-safety study assessed the efficacy of transvaginal RF treatment in the quality of life (QOL) and frequency of incontinence episodes in women with SUI. Methods: Twenty-eight women suffering from SUI were treated with an intravaginal quadric applicator while a grounding pad was attached in front of their pubes. The first phase is thermic, which will heat up the vaginal wall up to 40°C for 10 minutes. The second step is contraction to stimulate an aerobic exercise of pelvic floor muscles for 20 minutes (pulsed contractile RF at 20-40 watts and 1000-300 kHz with a modulation of 1 to 300 Hz for muscle exercise). It was scheduled for one session per week for 3 sessions. Patients had follow-up visits before and 1, 6 and 12 months following the treatment for one-day voiding diary, Persian version of urinary incontinence QOL questionnaire (I-QOL), Q-tip test, 24 hours-pad test and daily incontinence episodes’ number. Results: The patients’ mean age, duration of incontinence and median vesical leak point pressure were 41.6±9.6 years, 5.48±6.84 years and 140 cm H2 O respectively. Significant changes were observed in the mean I-QOL total score and the pad test. Also, a notable reduction was observed in the number of daily leakage episodes and the Q-tip test at any follow-up visit (P=0.001). Conclusion: Preliminary results suggest that transvaginal RF is a convenient method of SUI treatment. Significant changes were observed in the mean I-QOL total score and the pad test. Also, a notable reduction was observed in the number of daily leakage episodes.
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Harzer, Carla Sophie, Roberta Karla Francesca Della Bella e Hubert Andreas Gasteiger. "Cathode Loading Impact on PEM Fuel Cell Performance Losses in Voltage Cycling Based Accelerated Stress Tests". ECS Meeting Abstracts MA2023-02, n.º 37 (22 de dezembro de 2023): 1775. http://dx.doi.org/10.1149/ma2023-02371775mtgabs.
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In order to reach the target of carbon neutrality by the end of 2050 set by the European Union, hydrogen technologies will play an important role in supporting the transition to a renewable energy economy, especially for heavy duty applications, such as trucks and airplanes.1 For the latter, hydrogen is a viable alternative fuel compared to kerosene, offering a higher specific energy density as well as zero in-flight CO2 emissions.2 However during operation, proton exchange membrane fuel cells (PEMFCs) suffer from significant performance losses due to the instability of Pt-based catalysts for the oxygen reduction reaction (ORR) via the loss of electrochemically active surface area (ECSA).3 This induces substantial decay in the H2/air performance mainly due to the increasing impact of the local O2 transport resistance (RO2,local) with decreasing cathode roughness factor (rf, in units of cm2 Pt cm-2 MEA), which is especially pronounced for low Pt-loadings.4 Thus, for heavy duty applications requiring long-term durability, higher Pt loadings are required to reduce the impact of RO2,local. In this study, we analyse the H2/air performance loss contributions during voltage cycling based accelerated stress tests (ASTs) using cathodes with different Pt-loadings. ASTs were performed using 5 cm2 MEAs with cathode Pt loadings of 0.2, 0.4, and 0.8 mgPt cmMEA -2 (48.6 wt%, TEC10V50E, Tanaka Kikinzoku K.K. (TKK)). Full characterization of the MEA performance characteristics after different numbers of voltage cycles, was performed by measuring: i) H2/O2 and H2/air polarization curves; ii) cathode rf, determined by cyclic voltammetry and CO stripping; iii) O2 transport resistances (RO2,total) via limiting current measurements; and, iv) proton conduction resistances in the cathode catalyst layer (RH+,cath) via electrochemical impedance spectroscopy (EIS). Voltage cycling was performed under H2/N2 (200/75 nccm) at 80 °C, 95% RH, and ambient pressure using square wave profiles with lower and upper potential limits of 0.60 and 0.95 V, respectively, with hold times of 1 s at each potential. A strong H2/air performance dependency on the cathode rf is visible for the same Pt/C cathode catalyst with varying Pt loading. As shown in Figure 1, the same H2/air performance is reached at similar cathode rf values, independent of number of voltage cycles. This is due to the observation that the RO2,local values only depend on the cathode rf and not on the electrode’s history. Finally, when choosing an end-of-life (EoL) criterion of a more than 20 mV deviation of the measured cell voltages at a given current density from the theoretical ORR kinetics losses (c.f. red line in Figure 1 and gray areas for accepted cell voltage range), this EoL criterion is reached for the differently loaded MEAs at the same cathode rf but after different amounts of aging cycles. For example, at 1.5 A cm2 MEA this 20 mV deviation is reached at a cathode rf of 50-70 mgPt 2 cmMEA -2. However, for the 0.8 mgPt cmMEA -2 Pt/C cathode more than 200.000 cycles are needed to reach this value, compared to only 5.000 cycles for the 0.2 mgPt cmMEA -2 loaded cathode. Consequently, a 4-fold increase of the the cathode Pt loading increases its voltage cycling stability by »40-fold. References: "A European Green Deal - Striving to be the first climate-neutral continent", European Commission, (accesssed: 06/03/2023). C. Koroneos, A. Dompros, G. Roumbas, and N. Moussiopoulos, Resour Conserv Recycl, 44 (2), 99-113 (2005). G. S. Harzer, J. N. Schwämmlein, A. M. Damjanović, S. Ghosh, and H. A. Gasteiger, J. Electrochem. Soc., 165 (6), F3118-F3131 (2018). R. K. F. Della Bella, B. M. Stühmeier, and H. A. Gasteiger, Journal of The Electrochemical Society, 169 (4), 044528 (2022). Acknowledgement: We gratefully acknowledge funding from the German Federal Ministry for Digital and Transport (BMDV) under the funding scheme H2Sky (funding code 03B10706). R.K.F.D.B. also gratefully acknowledges funding from the German Federal Ministry for Economic Affairs and Energy (BMWi) under the funding scheme POREForm (funding number 03ET B027C). Figure 1: Correlation between the cathode roughness factor (rf) and the H2/air performance at different current densities over the course of a voltage cycling AST for MEAs using Pt/C cathodes with different Pt-loadings: 20,000 voltage cycles for 0.2 mgPt cmMEA -2 loadings, 200,000 voltage cycles for 0.4 mgPt cmMEA -2 loadings, and 500,00 voltage cycles for 0.8 mgPt cmMEA -2 loadings. Voltage cycling was done between 0.6 V and 0.95V using square wave modulation with 1s hold time. The red line describes the theoretical ORR kinetic induced losses based on DE = 70 mV×log(rf/rfinitial). The gray shaded areas visualize a 20 mV deviation from the theoretical ORR kinetics. Figure 1
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Astudillo, Leonardo Isaias, Roberta Karla Francesca Della Bella, Hubert Andreas Gasteiger, Carla Sophie Harzer, Franziska Carmen Hnyk, Timon Lazaridis e Christopher Warsch. "Accelerated Stress Tests to Project PEM Fuel Cell Durability". ECS Meeting Abstracts MA2023-02, n.º 43 (22 de dezembro de 2023): 2164. http://dx.doi.org/10.1149/ma2023-02432164mtgabs.
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One of the major degradation mechanisms limiting the long-term durability of proton exchange membrane fuel cells (PEMFCs) is the loss of platinum electrochemically active surface area (ECSA) of the carbon-supported platinum (Pt/C) cathode catalyst, caused by Pt dissolution that is followed by both Ostwald ripening of the Pt nanoparticles and loss of Pt into the ionomer phase [1]. The Pt ECSA loss is accelerated when subjecting PEMFCs to extended load-cycling inducing concomitant cycling of the cathode potential. To this end, accelerated stress tests (ASTs) can be conducted either by controlling the cell/stack current (“load-cycling” AST) under H2/air (anode/cathode) or the potential (“voltage-cycling” AST) under H2/N2 (anode/cathode). Most of the experiments studying the effect of load-cycling on catalyst durability have been based on voltage-cycling in a H2/N2 configuration, showing that Pt ECSA loss is aggravated with increasing upper potential limit (UPL), temperature, and relative humidity (RH) [2, 3, 4]. Comparing voltage-cycling induced degradation under H2/N2 versus H2/air, a recent study has found an essentially identical Pt ECSA loss, but a slightly higher H2/air performance decay when cycling under H2/N2 [4]. This study by General Motors Corporation indicates that Pt ECSA loss may not be a unique descriptor for H2/air performance loss, contrary to what was observed in recent work by Toyota Motor Corporation and Kyushu University [5] as well as in our own studies [6]. In this talk, we will discuss the correlation between H2/air performance loss and Pt ECSA loss during voltage-cycling ASTs at different conditions (UPL, RH, and gas-feed) conducted in 5 cm2 active area single-cell PEMFCs, complemented by a voltage-loss analysis to deconvolute oxygen reduction reaction (ORR) activity losses and mass transport losses (due to oxygen mass transport and proton conduction in the cathode catalyst layer). We will also discuss whether the H2/air performance loss is governed by the Pt ECSA loss (independent of catalyst loading) or, as we had proposed previously, by the cathode electrode roughness factor (rf) loss (in cm2 Pt/cm2 cathode, i.e., the product of ECSA and Pt loading) [7]. As roughly 100,000 [8] or even more voltage-cycles are expected for heavy-duty applications, requiring very long measurement times, an approach to relate the degradation under harsh AST conditions with those under application-relevant conditions will be discussed. Experiments are conducted with cathode catalysts based on different carbon supports (Vulcan, Ketjenblack, or so-called accessible carbon supports [9, 10]), on catalysts with different initial Pt ECSAs (i.e., different Pt nanoparticle sizes) and with different initial Pt-loadings (i.e. different initial rf). Finally, exploratory experiments to evaluate the effect of start-up/shut-down on the correlation between electrode rf and H2/air performance decay will be discussed. References: [1] P. J. Ferreira, G. J. la O’, Y. Shao-Horn, D. Morgan, R. Makharia, S. Kocha, H. A. Gasteiger, J. Electrochem. Soc . 152 (2005) A2256. [2] G. S. Harzer, J. N. Schwämmlein, A. M. Damjanović, S. Ghosh, H. A. Gasteiger; J. Electrochem. Soc. 165 (2018) F3118. [3] A. Kneer, N. Wagner; J. Electrochem. Soc. 166 (2019) F120. [4] S. Kumaraguro (General Motors), “Durable High Power Membrane Electrode Assembly with Low Pt Loading“; 2021 Annual Merit Review Meeting of the DOE Hydrogen Program (avail. online). [5] T. Takahashi, T. Ikeda, K. Murata, O. Hotaka, S. Hasegawa, Y. Tachikawa, M. Nishihara, J. Matsuda, T. Kitahara, S. M. Lyth, A. Hayashi, K. Sasaki; J. Electrochem. Soc. 169 (2022) 044523. [6] L. I. Astudillo, H. A. Gasteiger; to be submitted. [7] R. K. F. Della Bella, B. M. Stühmeier, H. A. Gasteiger; J. Electrochem. Soc. 169 (2022) 044528. [8] R. Borup, A. Weber, R. Ahluwalia, R. Mukundan, D. Myers, K. C. Neyerlin, “Million Mile Fuel Cell Truck Consortium“; 2021 Annual Merit Review Meeting of the DOE Hydrogen Program (avail. online). [9] V. Yarlagadda, M. K. Carpenter, T. E. Moylan, R. S. Kukreja, R. Koestner, W. Gu, L. Thompson, A. Kongkanand; ACS Energy Lett. 3 (2018) 618. [10] T. Lazaridis, H. A. Gasteiger; J. Electrochem. Soc. 168 (2021) 114517. Acknowledgement: We gratefully acknowledge financial support from various projects that enabled to conduct these studies: from the German Federal Ministry for Economic Affairs and Energy (BMWi) under the funding scheme POREForm (funding number 03ET B027C), from the Swiss National Science Foundation under the Sinergia grant number 180335, from the German Federal Ministry for Digital and Transport (BMDV) under the funding scheme H2Sky (funding code 03B10706), and from the Fuel Cells and Hydrogen 2 Joint Undertaking (JU) under the MORELife grant agreement 101007170.
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Della Bella, Roberta Karla Francesca, Björn Marcel Stühmeier e Hubert Andreas Gasteiger. "Universal Correlation between the Roughness Factor and PEMFC Performance Losses in Voltage Cycling Based Accelerated Stress Tests". ECS Meeting Abstracts MA2022-01, n.º 35 (7 de julho de 2022): 1427. http://dx.doi.org/10.1149/ma2022-01351427mtgabs.
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During operational lifetime, proton exchange membrane fuel cells (PEMFCs) suffer from high performance losses. For the year 2025, the U.S. Department of Energy (DoE) set the durability target for PEMFC light-duty transportation applications at 5,000 hours.1 To meet the automotive target, different aging protocols were established in order to simulate load cycle variations.2 It is well known that load or voltage cycling induces substantial catalyst degradation due to an increasing loss of electrochemically active surface area (ECSA), which is known to be a main driver for the resulting performance penalties.3 Thus, an increasing interest exists in developing accelerated stress test (AST) protocols that can sufficiently describe the degradation of the different components of a membrane electrode assembly (MEA) during automotive application using shorter measurement times. In this study, we report on a strategy to predict the performance degradation of an MEA, making use of a strongly accelerated voltage cycling based ASTs. For this, voltage cycling based ASTs were performed using 5 cm2 MEAs with a 0.1 mgPt cmMEA -2 loaded Pt/C catalyst (TEC10V20E, Tanaka) for both cathode and anode. Voltage cycling was done under H2/N2 (200/75 nccm) at 80 °C, 95% RH, and ambient pressure using square wave profiles with a constant lower potential limit (LPL) of 0.6 V and different upper potential limits (UPLs) of 0.85, 0.95, and 1.0 V, with LPL/UPL hold times of 1, 2, or 8 s. Full characterization of the MEA at beginning-of-life and after each set of voltage cycling intervals was performed by: i) measuring H2/O2 and H2/air polarization curves; ii) determining the ECSA by cyclic voltammetry and CO stripping; iii) conducting limiting current measurement to calculate the O2 transport resistance (R O2 total); and, iv) conducting electrochemical impedance spectroscopy (EIS) measurements under blocking conditions to quantify the proton conduction resistance in the cathode catalyst layer (R H+ cath). When the ECSA loss ranges between ≈20-85%, it was found that the ECSA decreases approximately linearly when plotted against the logarithm of the number of cycles (see fig. 1), exhibiting higher slopes for procedures with higher UPLs and longer hold times, in agreement with the results from previous studies.3, 4 In addition, a direct and AST protocol independent correlation between the loss in total available surface area, i.e., the roughness factor (rf ≡ ECSA × Pt-loading), and the individual loss contributions in H2/air performance curves, namely kinetic (mass/specific activity for the oxygen reduction reaction (ORR)) and O2 transport resistance contributions, was shown. This is due to the fact, that these individual voltage losses are not only highly affected by the cathode rf,3, 5 but that the Pt dissolution/redeposition mechanism seems to be identical for all of the here investigated voltage cycling ASTs, despite the largely varying UPLs and hold times. As a result, a universal correlation between the H2/air performance losses and the rf deterioration was found throughout all ASTs. The important corollary of this finding is that the data from quickly degrading voltage cycling ASTs (i.e., with high UPL) can be used to project the H2/air performance losses when cycling under less degrading conditions. References: "Fuel Cell Technologies Program Multi-Year Research, Development, and Demonstration Plan", U.S. Department of Energy, (2005, revision: 2012, accessed: 30/11/2021), https://www.energy.gov/eere/fuelcells/articles/hydrogen-and-fuel-cell-technologies-office-multi-year-research-development. R. Petrone, D. Hissel, M. C. Péra, D. Chamagne, and R. Gouriveau, Int. J. Hydrog. Energy, 40 (36), 12489-12505 (2015). G. S. Harzer, J. N. Schwämmlein, A. M. Damjanović, S. Ghosh, and H. A. Gasteiger, J. Electrochem. Soc., 165 (6), F3118-F3131 (2018). A. Kneer, N. Wagner, C. Sadeler, A.-C. Scherzer, and D. Gerteisen, J. Electrochem. Soc., 165 (10), F805-F812 (2018). T. A. Greszler, D. Caulk, and P. Sinha, J. Electrochem. Soc., 159 (12), F831-F840 (2012). Acknowledgement: We gratefully acknowledge funding from the German Federal Ministry for Economic Affairs and Energy (BMWi) under the funding scheme POREForm (funding number 03ET B027C). Figure 1 : Loss of normalized cathode ECSA over the course of voltage cycling. The aging procedure was done by voltage cycling between 0.6 V and different UPL (0.85, 0.95, and 1.0 V) using square wave modulation with varying LPL/UPL hold times (1, 2, and 8 s). The red dashed line describes the minimum ECSA value (≈15% normalized ECSA, corresponding to an rf of ≈12 cmPt cmMEA -2) for that a linear trend of ECSA vs. log(cycles) was observed. Figure 1
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Bergoli, César Dalmolin, Rodrigo Furtado de Carvalho, Ivan Balducci, Josete Barbosa Cruz Meira, Maria Amélia Máximo de Araújo e Marcia Carneiro Valera. "Influence of Fiber Post Cementation Length on Coronal Microleakage Values in vitro and Finite Element Analysis". Journal of Contemporary Dental Practice 15, n.º 4 (2014): 444–50. http://dx.doi.org/10.5005/jp-journals-10024-1560.
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ABSTRACT Aim This study aims to evaluate, the influence of different fiber posts cementation lengths by finite element analysis (FEA) and coronal microleakage. Materials and methods Fifty anterior bovine teeth were sectioned to obtain roots with 16 mm length. The coronal length of the post was 6 mm for all groups, while the radicular length were varied 6, 8, 10 or 12 mm. The fiber posts surfaces were cleaned with alcohol and silanized. Then the posts were cemented using a two steps total etch-and-rinse adhesive system + conventional resin cement. Forty teeth were submitted to mechanical cycling (45°; 2.000.000 cycles; 90N; 4Hz; 37°C) and ten teeth with radicular length of 12 mm was not submitted, serving as control. So, the experimental design was composed by different ratios of post coronal length/post radicular length and mechanical cycling (MC): Gr1- 1/1 + MC; Gr2- 3/4 + MC; Gr3- 3/5 + MC; Gr4- 1/2 + MC. All groups were immersed in a 1% toluidine blue solution. After 24 hours, the teeth were longitudinally sectioned and the microleakage scores was given by a blind operator. Data were submitted to Kruskal-Wallis test (p = 0.05). The experimental variables were simulated in twodimensional finite element analysis (2D-FEA). The maximum principal stress distributions were compared. Results No difference was observed in microleakage values between the cycled groups, whilst the control groups showed the lowest values. FEA analysis showed similar maximum principal stress distribution between the groups. Conclusion Mechanical cycling affected the values of coronal microleakage and different cementation length generated similar values of coronal microleakage and stress distribution. Clinical significance These results showed that from the microleakage point of view, more conservative cementation lengths have the same effect as longer cementation lengths. How to cite this article Bergoli CD, de Carvalho RF, Balducci I, Meira JBC, de Araújo MAM, Valera MC. Influence of Fiber Post Cementation Length on Coronal Microleakage Values in vitro and Finite Element Analysis. J Contemp Dent Pract 2014; 15(4):444-450.
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Della Bella, Roberta Karla Francesca, Björn Marcel Stühmeier e Hubert Gasteiger. "Universal Correlation between Cathode Roughness Factor and H2/Air Performance Losses in Voltage Cycling-Based Accelerated Stress Tests". Journal of The Electrochemical Society, 15 de abril de 2022. http://dx.doi.org/10.1149/1945-7111/ac67b8.
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Abstract The loss of electrochemically active surface area (ECSA) in the cathode during load cycling remains a major durability issue for proton exchange membrane fuel cells (PEMFCs). Here, the degradation of low-loaded cathodes (0.1 mgPt cmMEA −2) was investigated by accelerated stress tests (ASTs) in H2/N2 configuration, varying the upper potential limit (UPL, 0.85-1.0 V) and the hold time (1, 2, or 8 s) of the square wave voltage cycling profiles. A full voltage loss analysis was performed at beginning-of-life and after 100, 300, 1k, 2k, 5k, 10k, 20k, 50k, 100k, 200k, and 500k cycles, determining: i) the roughness factor (rf) via CO-stripping; ii) the H2-crossover; iii) the cathode electrode’s proton conduction resistance; iv) the H2/O2 and H2/air performance; and, v) the O2 transport resistance. It was found that the ECSA/rf deteriorates linearly versus the logarithm of the number of cycles or time at UPL, with higher slopes for harsher ASTs. The individual voltage losses were found to be either unaffected by the aging (H2-crossover and proton conduction resistance) or depend exclusively on the cathode rf (mass/specific activity and O2 transport resistances), independent of the AST procedure. This results in a universal correlation between H2/air performance and rf during voltage cycling ASTs.
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Behera, Subhashree, Swathi Ippili, Venkatraju Jella, Na‐Yeong Kim, Seong Cheol Jang, Ji‐Won Jung, Soon‐Gil Yoon e Hyun‐Suk Kim. "Confluence of ZnO and PTFE Binder for Enhancing Performance of Thin‐Film Lithium‐Ion Batteries". ENERGY & ENVIRONMENTAL MATERIALS, 20 de março de 2024. http://dx.doi.org/10.1002/eem2.12734.
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Developing anode materials with high specific capacity and cycling stability is vital for improving thin‐film lithium‐ion batteries. Thin‐film zinc oxide (ZnO) holds promise due to its high specific capacity, but it suffers from volume changes and structural stress during cycling, leading to poor battery performance. In this research, we ingeniously combined polytetrafluoroethylene (PTFE) with ZnO using a radio frequency (RF) magnetron co‐sputtering method, ensuring a strong bond in the thin‐film composite electrode. PTFE effectively reduced stress on the active material and mitigated volume change effects during Li+ ion intercalation and deintercalation. The composite thin films are thoroughly characterized using advanced techniques such as X‐ray diffraction, scanning electron microscopy, and X‐ray photoelectron spectroscopy for investigating correlations between material properties and electrochemical behaviors. Notably, the ZnO/PTFE thin‐film electrode demonstrated an impressive specific capacity of 1305 mAh g−1 (=7116 mAh cm−3) at a 0.5C rate and a remarkable capacity retention of 82% from the 1st to the 100th cycle, surpassing the bare ZnO thin film (50%). This study provides valuable insights into using binders to stabilize active materials in thin‐film batteries, enhancing battery performance.
Teses / dissertações sobre o assunto "RF stress and thermic cycling"
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Pinault, Bastien. "Évaluation de topologies d'amplificateurs faible bruit et robustes en filière GaN pour applications radar ou télécom en bande X". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSES070.
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Dans l'optique d'accroitre les débits des télécommunications ainsi que la précision et la portée de détection des systèmes radars modernes, l'amélioration du facteur de bruit d'une liaison est devenue essentielle. Comme le démontre la formule de FRIIS , le facteur de bruit d'une architecture de réception est majoritairement déterminé par le facteur de bruit du premier étage. Il apparait alors nécessaire de placer en amont de cette dernière un amplificateur faible bruit (LNA). Ce dernier peut être confronté à des agressions électromagnétiques (EM) pouvant détériorer, voir rendre inopérant le système, en fonction de l'application visée. Il est donc nécessaire de concevoir des LNA robustes vis-à-vis de ces agressions EM. Par leurs caractéristiques intrinsèques (large bande interdite, tension de claquage élevée et bonne conductivité thermique...) les technologies nitrure de gallium (GaN) sont d'excellentes candidates pour l'implémentation d'amplificateur faible bruit. En effet, la robustesse naturelle offerte par ce matériau permet de s'affranchir des dispositifs de protection tels que les limiteurs de puissance utilisés en technologie GaAs ou SiGe. Les contraintes des systèmes modernes poussent ces derniers à maintenir leurs caractéristiques même lorsqu'ils sont soumis à des agressions EM. Les topologies d'amplificateurs faible bruit doivent donc pouvoir répondre au double objectif de forte détectivité (faible facteur de bruit HF) et de grande linéarité (forte puissance) aux fréquences d'utilisation. Afin d'augmenter la linéarité d'un LNA, une stratégie consiste à surdimensionner le transistor (dimensions physiques ou électriques plus importantes que celles nécessaires pour un facteur de bruit optimal). Les performances non linéaires se trouvent alors améliorées au détriment des paramètres de bruits et/ou petits signaux. Cette thèse propose une nouvelle approche permettant d'exploiter simultanément les caractéristiques non linéaires d'une conception de LNA initialement optimisée sur les paramètres de bruit en améliorant le comportement non-linéaire de l'élément actif via un changement de son point de repos. Cette stratégie oblige à des études plus poussées sur la stabilité de tels systèmes, et des chemins critiques de repolarisation, toujours délicats à appréhender pour les technologies nitrures. Une étude comparative ainsi qu'un état de l'art plus global permet de situer notre solution dans le spectre des possibilités offertes dans l'optique d'obtenir un système faible bruit et robuste. Des tests dynamiques et en bruit HF avant et après contraintes sous signal RF par créneau vient appuyer l'approche proposéeIn order to increase telecommunication data rates and enhance the precision and range of modern radar systems, improving the noise factor of a communication link has become crucial. As demonstrated by the FRIIS formula, the noise factor of a reception architecture is mainly determined by the noise factor of the first stage. It is, therefore, necessary to place a low-noise amplifier (LNA) upstream of the first stage. LNAs may face electromagnetic (EM) aggressions that can degrade or even render the system inoperative, depending on the intended application. Hence, it is essential to design LNAs that are robust against these EM aggressions. Due to their intrinsic characteristics (wide bandgap, high breakdown voltage, and good thermal conductivity), gallium nitride (GaN) technologies are excellent candidates for implementing low-noise amplifiers. The natural robustness offered by this material allows for the elimination of protection devices such as power limiters used in GaAs or SiGe technologies. Modern system constraints compel them to maintain their characteristics even when subjected to EM aggressions. Low-noise amplifier topologies must, therefore, meet the dual objective of high detectivity (low HF noise factor) and high linearity (high power) at usage frequencies. To increase the linearity of an LNA, one strategy involves oversizing the transistor (physical or electrical dimensions larger than those necessary for optimal noise factor). This approach improves nonlinear performance at the expense of noise parameters and/or small signals. This thesis proposes a novel approach that simultaneously exploits the nonlinear characteristics of an LNA design initially optimized for noise parameters by enhancing the nonlinear behavior of the active element through a change in its operating point. A comparative study and a broader state-of-the-art analysis position our solution within the spectrum of possibilities for achieving a low-noise and robust system
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Peretti, Vanni. "Development of reliable RF-MEMS switches for antennas and space applications". Doctoral thesis, Università degli studi di Padova, 2008. http://hdl.handle.net/11577/3425657.
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Radio Frequency Micro Electro Mechanical (RF-MEMS) components are a contender for future
low-power high-frequency wired reconfigurable networks and wireless communication
systems. In many RF applications, a single MEM component can replace and outperform an
entire solid-state circuit; in other applications, a judicious association of MEMS with active
devices will result in smart communicating circuits and systems. These MEMdevices have the
potential to surpass the limits of today’s equivalent implementations that use only traditional
solid-state technology. However, the scarce maturity of this technology makes these devices
suffering of severe reliability issues. The purpose of this thesis is to investigate the reliability
of RF-MEMS switches, starting from common measurements tests, like cycling and DC characterization,
to more particular stresses, like Electro Static Discharge (ESD) or Radiations for
space applications qualification.Gli switchMicro-Elettro Meccanici per Radio Frequenza (RF-MEMS) sono tra i dispositivi più promettenti per le future generazioni di network riconfigurabili ad alta frequenza e basso consumo di potenza. Vi sono applicazioni RF in cui un singolo dispositivo MEMS può sostituire e migliorare in termini di prestazioni un intero circuito a stato solido; in altri campi invece, un opportuno connubio fra tecnologia MEMS e dispositivi attivi può portare alla nascita di sistemi di comunicazioni estremamente brillanti e performanti. Infatti, i dispositivi MEMS hanno in loro le potenzialità per sorpassare i limiti delle attuali tecnologie impiegate basate su circuiti integrati. Tuttavia, la mancanza di maturità di una tecnologia così innovativa porta con sé inevitabili problemi affidabilistici. L’obbiettivo di questa tesi è di analizzare l’aspetto affidabilistico degli switch RF MEMS, cominciando da metodi comuni di caratterizzazione e stress, come la caratterizzazione DC e il Cycling stress, fino a test più specifici, come la robustezza a scariche elettrostatiche (ESD) o il monitoraggio di danni indotti da radiazione per la qualificazione dei dispositivi per missioni spaziali.
Trabalhos de conferências sobre o assunto "RF stress and thermic cycling"
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Motalab, Mohammad, Munshi Basit, Jeffrey C. Suhling e Pradeep Lall. "A Revised Anand Constitutive Model for Lead Free Solder That Includes Aging Effects". In ASME 2013 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ipack2013-73232.
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Traditional finite element based predictions for solder joint reliability during thermal cycling accelerated life testing are based on solder constitutive equations (e.g. Anand viscoplastic model) and failure models (e.g. energy dissipation per cycle model) that do not evolve with material aging. Thus, there will be significant errors in the calculations with lead free SAC alloys that illustrate dramatic aging phenomena. In this study, we have developed a revised set of Anand viscoplastic stress-strain relations for solder that include material parameters that evolve with the thermal history of the solder material. The effects of aging on the nine Anand model parameters have been examined by performing stress-strain tests on SAC305 samples that were aged for various durations (0–6 months) at temperature of 100 C. The stress-strain data were measured at three strain rates (.001, .0001, and .00001 1/sec) and five temperatures (25, 50, 75, 100, and 125 C). The mechanical tests have been performed using both water quenched (WQ) and reflowed (RF) 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. As expected, the observed mechanical properties of water quenched samples were better (higher in magnitude) than the corresponding mechanical properties of the reflowed samples. Although the differences in elastic modulus between the water quenched and reflowed samples are small, significant differences are present for the yield and ultimate tensile stresses (for each aging condition). For both the water quenched and reflowed specimens, significant degradation of the mechanical properties has been observed with aging. Using the measured stress-strain and creep data, mathematical expressions have been developed for the evolution of the Anand model parameter with aging time. Our results show that 2 of the 9 constants remain essentially constant during aging, while the other 7 show large changes (30–70%) with up to 6 months of aging. The revised Anand constitutive equations for solder with aging effects have also been incorporated into commercial finite element codes (ANSYS and ABAQUS).
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Basit, Munshi, Mohammad Motalab, Jeffrey C. Suhling e Pradeep Lall. "Viscoplastic Constitutive Model for Lead-Free Solder Including Effects of Silver Content, Solidification Profile, and Severe Aging". In ASME 2015 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems collocated with the ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/ipack2015-48619.
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In the electronic packaging industry, it is important to be able to make accurate predictions of board level solder joint reliability during thermal cycling exposures. The Anand viscoplastic constitutive model is often used to represent the material behavior of the solder in finite element simulations. This model is defined using nine material parameters, and the reliability prediction results are often highly sensitive to the Anand parameters. In this work, an investigation on the Anand constitutive model and its application to SAC solders of various Ag contents (i.e. SACN05, with N = 1, 2, 3, 4) has been performed. For each alloy, both water quenched (WQ) and reflowed (RF) solidification profiles were utilized to establish two unique specimen microstructures, and the same reflow profile was used for all four of the SAC alloys so that the results could be compared and the effects of Ag content could be studied systematically. In addition, we have performed tensile testing on reflowed specimens subjected to 6 months of aging at 100 C. After this level of aging, any further changes in the mechanical response and properties will be rather small. Thus, the results for these tests can be regarded as approaching the highest level of mechanical behavior degradation possible for a “severely aged” lead free solder material. The nine Anand parameters were determined for each unique solder alloy and microstructure from a set of stress strain tests performed at several strain rates and temperatures. Testing conditions included strain rates of 0.001, 0.0001, and 0.00001 (sec−1), and temperatures of 25, 50, 75, 100, and 125 C. As expected, the mechanical properties (modulus and strength) increase with the percentage of Ag content, and these changes strongly affect the Anand parameters. The sensitivity of the mechanical properties and Anand parameters to silver content is higher at lower silver percentages (1–2%). Also, the observed mechanical properties of water quenched samples were better (higher in magnitude) than the corresponding mechanical properties of the reflowed samples. Although the differences in elastic modulus between the water quenched and reflowed samples are relatively small, significant differences are present for the yield and ultimate tensile stresses of all four SAC alloys. The changes in the Anand model parameters after severe aging (6 months at 100 °C) were significant. The measured experimental results have been used to illustrate the range of values possible for Anand parameters for the SACN05 alloys. The upper extreme was the water quenched limit, where the materials have extremely fine microstructures and high mechanical properties. The lower extreme was the severely aged limit, where the materials have extremely coarsened microstructures and highly degraded mechanical properties. While further degradations are certainly possible with even further aging, the limiting values found for a severely aged SAC alloy can be used by designers as a conservative set of constitutive parameters representing the lower end of the material properties for that alloy. After deriving the Anand parameters for each alloy and microstructure, the stress-strain curves have been calculated for various conditions, and excellent agreement was found between the predicted results and experimental stress-strain curves.
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Khinda, Gurvinder Singh, Ashraf Umar, Ryan J. Cadwell, Mohammed Alhendi, Nancy C. Stoffel, Peter Borgesen e Mark D. Poliks. "Flexible inkjet-printed Patch antenna array on mesoporous PET substrate for 5G applications with stable RF performance after mechanical stress cycling". In 2020 IEEE 70th Electronic Components and Technology Conference (ECTC). IEEE, 2020. http://dx.doi.org/10.1109/ectc32862.2020.00285.
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Cunningham, Shawn J., Yvonne Heng, Nabeel Idrisi, Brad Nelson e John McKillop. "Flip Chip Packaging of Wafer Level Encapsulated RF MEMS Tunable Capacitors". In ASME 2013 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ipack2013-73222.
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Wireless handheld communications has identified significant benefits of tuning that include fewer dropped calls, increased battery life and improved user experience. The tuning can be part of the antenna, power amplifier (PA), filtering, or part of a fully integrated radio front end (FE). RF MEMS tunable capacitors have been integrated with 0.18 μm RF HVCMOS to address the need for tuning in wireless communications. These integrated, MEMS tunable capacitors are hermetically encapsulated at the wafer level, but the integrity of the encapsulation must be maintained during BEOL operations. The BEOL operations include shipping and handling, passivation coat and cure, solder bumping (screen printed or electroplated), backside grinding (BSG), dicing, and pick and place. In this paper we will describe, the flip chip packaging of the wafer level encapsulated MEMS devices including finite element analysis. The flip chip packaging of ASIC die is primarily concerned with solder bump reliability during such qualification stresses as temperature cycling and drop testing. The flip chip packaging of a wafer level encapsulated MEMS device has additional concerns that include encapsulation integrity and device package sensitivity. The die thickness, underfill, and encapsulation dimension have been varied to minimize the deflection and stress associated with the encapsulation. The primary failure mode associated with the overstress of the encapsulation is a cracked lid that will lead to the ingress of moisture and a rise in the cavity pressure from to atmospheric conditions. The failure can be detected by an increase in the MEMS switching time and frequency response or by a return to zero failure (RTZ) associated with device stiction. A low modulus and low CTE UF has been implemented for the lowest deflection and stress. The lowest deflection and stress is provided by eliminating the UF, but this is not feasible for the purpose of solder bump reliability. In practice, the MEMS encapsulation is robust to the printed solder bumping process that includes placement and removal of the bump screen and the squeegee of solder past into the solder screen. The MEMS encapsulation is robust to the attachment and removal of BSG tape and the pressures associated with BSG. The final dicing operation has not demonstrated any detrimental impact on the MEMS encapsulation. The final demonstration of success is the assembly of the MEMS tunable capacitor die to a laminate substrate using lead-free solder and underfill.
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Park, Jun-Hyub, Man Sik Myung e Yun-Jae Kim. "Specimen Size Effect on Fatigue Properties of Surface-Micromachined Al-3%Ti Thin Films". In 2007 First International Conference on Integration and Commercialization of Micro and Nanosystems. ASMEDC, 2007. http://dx.doi.org/10.1115/mnc2007-21280.
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This paper presents high cycle fatigue properties of an Al-3%Ti thin film, used in a RF (radio-frequency) MEMS switch for a mobile phone and also describes new test method for obtaining static and dynamic characteristics of thin film and reliability evaluation method on MEMS device with thin film developed by authors. Durability should be ensured for such devices under cycling load. Therefore, with the proposed specimen and test procedure, tensile and fatigue tests were performed to obtain mechanical and fatigue properties. The specimen was made with dimensions of 1000μm long, 1.0μm thickness, and 3 kinds of width, 50, 100 and 150μm. High cycle fatigue tests for each width were also performed, from which the fatigue strength coefficient and the fatigue strength exponent were found to be 193MPa and −0.02319 for 50μm, 181MPa and −0.02001 for 100μm, and 164MPa and −0.01322 for 150μm, respectively. We found that the narrower specimen is, the longer fatigue life of Al-3%Ti is and the wider specimen is, the more susceptible to stress level fatigue life of Al-3%Ti was.