Temperature Cycling Conditions Research Articles

Mechanical properties and multiscale structure evolution of cement mortars under temperature cycling and low-humidity coupled condition

The degradation of concrete induced by wide temperature differences and drying significantly impacts the durability of constructions in plateau regions. This study systematically investigated the mechanical properties, the structure evolution from nanoscale to macroscale, and the hydration product changes under temperature cycling with low relative humidity (5–60°C cycling, 30±5 % RH). Damage gradients were meticulously discussed based on the experimental measured thermal gradient and mechanical failure modes. Pore coarsening and microcracks which increased with w/c mainly occurred between 50 nm and 50 μm, becoming key factors contributing to the mechanical degradation. Nevertheless, the relatively small damages enable the mortar to maintain much stable mechanical properties than cement paste and concrete. The hydration and the small amount of decomposition had little effect on the structure. Overall, the strength increased until a certain time window followed by a decreasing trend because of two contradictory factors: enhancement led by the increase of capillary pressure and surface energy and degradation driven by the gradient damage.

Water-salt transport modeling and sulfate erosion mechanisms in cultural heritage under microclimate

The microclimate of the environment influences the characteristics of salt erosion in historical cultural heritage, determining the pattern of salt weathering and the mechanism of salt-action. The study focuses on the influence of cultural heritage microclimate on salt weathering, and the study aims to understand the weathering mechanism by combining the theory of crystalline weathering with temperature and humidity variation. The study comprised immersing sandstone from the Yungang Grottoes, a World Heritage Site, in a sulfate salt solution and simulation of salt deterioration under on-site cyclic variable temperature and humidity conditions. The article designs the accumulation of salt crystallization at the sandstone surface under the effect of salt evaporation and visualizes the water-salt migration and crystallization process by ion chromatography (IC), microelectrode, and hyperspectral techniques. The corresponding types of sulfate deterioration under different weathering simulation conditions are investigated to probe the mechanism behind different weathering patterns. In the first part, we construct a water-salt migration test, combining hyperspectral techniques and microelectrodes to visualize the weathering patterns, compositional characteristics, and spatial and temporal changes of water-salt transport based on Fick's law to establish a mathematical model and simulate it in COMSOL multi-physics field simulation software. Subsequently, tests were carried out on sandstone with sulfate solution at variable temperatures and humidity levels to simulate the process of salt weathering. The results demonstrated that different salt solutions, such as Na2SO4 and MgSO4, lead to the dissolution of clay minerals. At the same time, crystallization disrupts the sandstone structure, causing degradation of its physico-mechanical properties after several weathering cycles, and there are significant differences in the salt crystallization patterns at different temperatures and after cycling at different humidities.

The snowball effect in electrochemical degradation and safety evolution of lithium-ion batteries during long-term cycling

Lifespan and safety are the most critical issues for the application of lithium-ion batteries (LIBs). During long-term service, the degradation mechanisms and safety evolution of LIBs remain unclear, posing significant obstacles to battery design and management. This study analyzes the electrochemical degradation mechanisms of LIBs under normal temperature cycling (NTC) and high-temperature cycling (HTC) conditions, linking these mechanisms to the evolution of battery safety. The findings reveal that during NTC, there is a “snowball effect” in performance degradation and safety evolution, leading to sudden death of battery and posing serious safety risks. The degradation pattern of LIBs during NTC and HTC is consistently dominated by the increase of internal resistance and the loss of lithium inventory (LLI). In the aging process, electrolyte consumption and the growth of the solid electrolyte interface (SEI) cause localized lithium plating on the anode, resulting in accelerated capacity decay. However, in batteries subjected to NTC, rapid accumulation of localized lithium plating can trigger a snowball effect, causing electrode deformation, internal short-circuit (ISC) and separator melting. These interacting catastrophic events form a vicious cycle, ultimately leading to battery sudden death and pose significant safety hazards. Additionally, thermal safety analysis reveals the correlation between thermal safety parameters and state of health (SOH), quantifying the thermal safety degradation caused by sudden death. Sudden death directly alters the evolution pattern of battery safety, leading to a severe decline in battery safety. These findings offer new insights into potential safety hazards associated with long-term use of LIBs.

An advanced ceramifiable organic-inorganic hybrid polysiloxane coating with superior moisture-resistant property

A ceramifiable organic-inorganic hybrid polysiloxane, prepared via a straightforward solution blending method, was successfully coated on the surface of silicon dioxide ceramic via a scrapping method. A uniform and dense lithium aluminum borosilicon (LABS) vitrified layer in situ formed on the surface of silicon dioxide ceramics was successfully prepared through liquid phase filling method to fulfill the moisture resistance requirements under high temperature cycle conditions. Effects of aluminum content on the microstructure change process and moisture resistance properties of the ceramifiable organic-inorganic hybrid polysiloxane have been systematically researched. With the increase of aluminum content, the ceramic yield of the hybrid polysiloxane and the heat loss capacity of LABS glass-ceramics increase. The crack-free and high temperature fluid vitrified layer endows the LABS glass-ceramic with excellent thermal shock resistance cycle ability, self-healing ability and moisture resistance. Results showed that the LABS vitrified coating with an aluminum-boron ratio of 1:2 presents the most appealing thermal shock cycle resistance and crack self-healing ability after 20 thermal cycles, as well as a water absorption rate of 0.3814 %. By refining the application of modified polysiloxane moisture-resistant coatings in high-temperature circulation environments, this work shed lights on the importance of in situ growth LABS vitrified coating in accelerating surface reconstruction and improving moisture resistance, incenting additional innovative breakthroughs in the LAS-based glass-ceramic materials design and fabrication within the aviation field.

Study on the degradation of welding strength in ceramic substrates subjected to temperature cycling

Abstract This article uses AlN and Al2O3 thick film substrates to conduct an in-depth study of the attenuation of welding strength of ceramic substrates under temperature cycling conditions. Using the test method of miniaturizing the substrate to test the transverse shear force, the shear force changes of different substrates with different 62Sn36Pb2Ag solder thicknesses were summarized and compared with the temperature cycle process. The finite element simulation method was used to simulate the Ag/SnPb interface, and the trend of interface stress and strain changing with temperature was obtained. Finally, the study found that during the temperature cycle, the Sn-enriched phase in the solder of the AlN substrate diffuses faster into the Ag layer, so the soldering strength of the AlN substrate decays faster during the temperature cycle.

Temperature Response of Double-Layer Steel Truss Bridge Girders

Double-layer steel truss continuous girders are prone to significant temperature stress, deviation, torsion, and warping, thus causing adverse temperature structural responses, and also affecting the safety and durability of bridge structures. This paper presents an investigation on time-dependent characteristics in the temperature field and temperature response of double-layer steel truss continuous bridge girders, fully considering the shielding effect subjected to different solar radiation angles during the high-temperature season. The time-dependent thermal boundary conditions and support conditions provided for the steel truss bridge structure were determined. Subsequently, a thermal analysis model for the entire structure of double-layer steel truss continuous girders was established to attain the temperature distribution law. The research results show that significant differences occur in the position and temperature difference of temperature gradients exhibited in the vertical, horizontal, and longitudinal directions in the double-layer steel truss bridge structure. The temperature distribution pattern within the chord section is mainly influenced by the environmental temperature and solar radiation intensity, along with the heat exchange between different panels. Thereafter, a validated temperature gradient formula for the component section has been proposed. The time-dependent laws in structural displacement, stress, and rotation angle under daily temperature cycling conditions have been revealed, thereby providing a theoretical basis for the life cycle construction and safety maintenance of double-layer steel truss structure bridges.

Degradation behavior of 21700 cylindrical lithium-ion battery cells during overdischarge cycling at low temperatures

Lithium-ion battery (LIB) cells are prone to overdischarge or overcharge when connected in series or parallel as a module or pack for large-format applications, such as electric vehicles (EVs) because of variations in battery capacities and difficulty in maintaining similar state-of-charge (SOC) of every single battery. However, the thermo-electrochemical behavior of LIBs during overdischarge has not been investigated at low temperatures. This study unveils the thermo-electrochemical behavior of overdischarged 21700 cylindrical LIB cells at −20 °C and 25 °C. Also, a thermo-electrochemical model was built to explain the heat generation within the cells and correlate them with the observed electrochemical characteristics. It was found that contrary to the severe cell degradation observed in the overdischarged cell compared to the standard cell at 25 °C, both cells show similar degradation behavior under low temperature cycling conditions. Thus, at low temperatures, overdischarge does not adversely affect cell degradation as observed at room temperature. This was attributed to the significant increase in the internal temperature, which results in improved electrochemical characteristics of the cell.

Study on interfacial leakage characteristics of rubber sealing under temperature cycle conditions in PEM fuel cell

The amount of leakage is the only direct indicator of the sealing performance of a proton exchange membrane fuel cell (PEMFC). In this work, a predictive model is developed to quantitatively evaluate the variation of leakage for a PEMFC under temperature cycling conditions. The method first uses the Lattice-Boltzmann method to simulate the gas flow within the contact interfacial gap at various heights. Then the finite element method is used to analyze the local and macroscale contact state of the sealing interface and to clarify the effect of contact stresses on the interfacial gap height. Finally, the generalized Maxwell model, which considers time-temperature transfer and stiffness growth, is used to calculate the interfacial contact stresses under temperature cycling. The validity of the model was verified by comparison with experimental data from the available literature. Further analysis showed that reduced start-up temperature exacerbated the stress relaxation effect and decreased the service life of the seal material. When the start-up temperature is reduced from 25 °C to −20 °C, the model predicts that the service life of the PEMFC will be reduced by 100 temperature cycles or more. The leakage variation in a cycle was also discussed, and it was found that the leakage fluctuation became more and more significant as the number of cycles increased, weakening system reliability.

Evaluation under temperature cycling of the tribological properties of Ag-SiNx films for green tribological applications

Nowadays, one of the most important challenges in the tribology field is to avoid the excessive consumption of soft metals such as Ag at elevated temperatures through the re-design of the self-lubricant films, to achieve the long-term lubricant under the temperature-cycling environments, for widely used in real industrial applications. This paper took up this challenge to develop a novel green film, by composing nano-particles Ag into the amorphous SiNx matrix using magnetron sputtering system, for achieving the long-term lubricant under the room temperature (RT)-500 °C temperature-cycling conditions. Results showed that the film exhibited a dual-phase of face-centered cubic (fcc) Ag and amorphous SiNx. An excellent RT-500 °C wear-resistance performance was observed for the films with the Ag content of 1.3–9.4 at.%, whilst the film at 15.8 at.% Ag exhibited the best anti-frictional performance (COF 0.3–0.5 for RT-500 °C conditions) at the cost of wear rate. The self-lubricant tribology behaviors under the RT-500 °C cycling conditions were mainly attributed by the synergism of: (1) mechanical properties, (2) excellent high-temperature chemical stability of SiNx matrix, and (3) the lubricant nature of Ag and its elevated temperature diffusion behaviors.

Effect of Polycyclic Aromatic Compounds on Electrical Treeing Growth in XLPE Insulation

This article focuses on the effect of polycyclic aromatic compounds (PACs) on the electrical tree of cross-linked polyethylene (XLPE) insulation for high-voltage (HV) cables. The XLPE insulation samples with or without PACs are prepared for electrical treeing degradation at constant and cyclic temperatures. The results show that the growth of the electrical tree within the XLPE/PACs insulation is retarded. The partial discharge (PD) amplitudes of XLPE/PACs insulation are significantly decreased during the treeing process compared to XLPE insulation. Furthermore, under cyclic temperature conditions, the tree growth of XLPE/PACs composites stagnates as the temperature decreases from 90 °C to 25 °C. Even when it rebounds to 90 °C, the treeing degradation of XLPE/PACs insulation is still retarded, resulting from a significant weakness of PD. The results show that the XLPE/PACs composites exhibit a greater electrical treeing resistance. Based on density functional theory (DFT), analysis of the excitation characteristics and density of states (DoS) reveals that the PACs absorb photon energy to prevent damage to insulation. In contrast, the excited PACs result in a cross-linking reaction to XLPE and introduce electron and hole traps, which capture hot electrons. The cross-linking product acts as localized states of electron traps and hole traps, which capture the high energy carriers during treeing. In summary, the PACs retard the growth of electrical trees and improve the insulation performance.

Long and Covalently Conjugated Branched DNA Structures for in Situ Gelation in Vivo

Long and Covalently Conjugated Branched DNA Structures for in Situ Gelation in Vivo

On the Microstructure Development under Cyclic Temperature Conditions during WAAM of Microalloyed Steels

This paper shed light on the kinetics of transformation and the developed microstructure during wire arc additive manufacturing (WAAM). Three microalloyed alloys, two of them are high strength low alloyed steel (HSLA) grades and the third is a Ni-Cr-Mo steel, from which the welding wires are being produced, were investigated. Repeated cycles around varied temperatures from a reheating temperature of 1350 °C and down to a temperature 35 °C below the Ae1 are applied using dilatometer on samples from the steels. After applying the cycles, the dilatometric-samples were investigated metallographically and their macro- and microhardness values were measured. It is shown that the WAAM using HSLA steels produce softer structure than the steel of the welding wire. Combined microalloying with Ti and Nb can present a useful strategy for producing finer structure in the WAAM components due to the effect of Ti in inhibiting the prior austenite grain-growth and that of Nb in refining the final structure. Additionally, repeated heating near Ae3 refines the prior austenite grains and produced fine ferrite-pearlite structure in case of HSLA steels and a microstructure predominated by the granular bainite in case of welding wire alloy. The former microstructure was the softest one for the case of HSLA steels, whereas the softest structure in case of the welding wire alloy was the tempered martensite structure developed by reheating below Ae1. Idealized temperature curves were chosen for the heat treatment, which could be characterized in a well-defined manner. In future work such idealized curves together with temperature histories obtained in WAAM-process will be used to set up a database to train an AI-model for predicting structure and material properties.

A Thermal Tanks-in-Series Model for Capacity Fade Validation Studies in Lithium-Ion Batteries

Lithium ion batteries are widely adopted due to their high energy density, low self-discharge rate and fast charging capabilities1. However, during their operation, capacity fade occurs as a result of various parasitic reactions causing loss of cyclable lithium ions. A dominant and widely studied fade mechanism is the formation of the Solid Electrolyte Interphase (SEI) layer caused by the reduction of electrolyte at the anode-electrolyte boundary. Temperature plays a crucial role on the electrochemical performance of individual cells, affecting the diffusivities of ions, kinetics of reactions and rate of degradation of the battery. Thermal battery models allow us to study the thermal behavior of cells and are often used for cell configuration optimization and thermal management system design2.In literature, thermal models are incorporated with empirical and physics-based models to capture battery dynamics influenced by temperature. Empirical thermal models are simple and fast to solve but are applicable only for specific operating conditions and cannot capture electrochemical subtleties. Conversely, physics-based models use equations that incorporate transport phenomena and electrochemical reactions occurring in the cell. Common physics-based models are the Single Particle Model (SPM) and the Psuedo-2D (P2D) model. The P2D model is robust but computationally expensive3 and the SPM model does not capture electrolyte transport which has a non-linear temperature dependence.The Thermal Tank-In-Series4,5 model is a systematically volume-averaged form of the P2D model with energy balance equations for the current collectors, cathode, separator and anode. This reduces the number of equations in the model and improves computational speed while maintaining accuracy. This model can be ideal to predict capacity fade during fast charging.Extending on our previous work, we take the Thermal Tanks-in-Series model coupled with SEI layer formation for a single-cell sandwich and apply it to analyze capacity fade under different temperature cycling conditions. Experimental validation of the model will facilitate understanding of diffusive, kinetic and temperature effects on the growth of the SEI layer and cell capacity fade. References M. Pathak, S. Kolluri, and V. R. Subramanian, J. Electrochem. Soc., 164, A973–A986 (2017).H. Liu, Z. Wei, W. He, and J. Zhao, Energy Convers. Manag., 150, 304–330 (2017).V. Ramadesigan et al., J. Electrochem. Soc., 159, R31–R45 (2012).A. Subramaniam, S. Kolluri, S. Santhanagopalan, and V. R. Subramanian, J. Electrochem. Soc., 167, 113506 (2020).A. Subramaniam et al., J. Electrochem. Soc., 167, 013534 (2020).

Characterization of Low Cobalt Cathode Degradation Using Distribution of Relaxation Times Analysis

High-capacity cathode materials with reduced or eliminated cobalt usage are being pursued for lithium-ion batteries (LIB) due to environmental and humanitarian issues in the cobalt supply chain. Consequently, increased nickel content and reduced cobalt content results in faster cell degradation. A connection between morphological and chemical changes within the cathode microstructure, charge cut-off voltage, and operating temperature has been developed through a combination of cycling conditions, X-ray Diffraction (XRD), and Distribution of Relaxation Times (DRT) analysis.Low cobalt half-cell batteries were fabricated with Li(Ni0.8Mn0.1Co0.1)O2 (NMC811) active material and tested under high cut-off voltage (4.3V), low cut-off voltage (4.0V), high temperature (60°C), and ambient temperature (25°C). XRD analysis of high cut-off voltage samples show a presence of NiOx crystalline structure, a low diffusivity rock-salt phase. To further understand the electrochemical changes due to the appearance of the rock-salt phase, DRT analysis was conducted on the electrochemical impedance spectra taken after formation of the solid electrolyte interphase (SEI) and after cycling. DRT analysis is becoming a preferred method of analysis due to the fact that electrochemical processes, like solid-state diffusion, cathode electrolyte interphase (CEI), and SEI formation, show up at characteristic frequencies, allowing for interpretation of changes that are often not visible within typical impedance plots. Prior to cycling, the primary contribution was initially found to be from the CEI and SEI. At low cut-off voltage cycling conditions, ambient temperature cycling showed that the contribution shifted from the CEI to diffusion resistance, but changes within the SEI and CEI were still detected. High temperature cycling conditions within the low cut-off voltage samples showed that the diffusion resistance again increased and the contributions from the CEI and SEI decreased. At high cut-off voltage cycling conditions, ambient temperature cycling showed that diffusion was becoming the main contribution but changes due to the CEI were still evident. High temperature cycling conditions in the high cut-off voltage samples showed that the mechanism was completely taken over by diffusion, due to the lithium transport being limited by the rock-salt phase or electrolyte degradation.XRD patterns confirmed that the rock-salt phase was beginning to form within the low cut-off voltage high temperature cycling condition, but in much lower intensity than that of the high cut-off voltage condition. This observation clearly shows that the diffusion mechanism, which hinders intercalation and deintercalation, is driven by the formation of the non-conductive rock-salt phase. While primarily influenced by cut-off voltage, elevated temperature may also contribute to this degradation mechanism. The combination of different electrochemical and microstructural characterization techniques supports this observation and demonstrate that DRT analysis is an effective method to better understand the driving mechanisms behind battery degradation.

Multilayer Mo2N-Ag/SiNx films for demanding applications: Morphology, structure and temperature-cycling tribological properties

Nowadays there is the need to avoid the excessive consumption of liquid lubricant oils, as they are harmful to the environment and hard to disposal. Self-lubricant films have been seen as the sustainable solution to achieve a long-term lubrication under high temperature-cycling conditions. In this manuscript, multilayer Mo2N-Ag/SiNx films with a fixed modulation ratio (thickness of Mo2N-Ag to SiNx) of 3:1, with changing modulation period (Λ, thickness of Mo2N-Ag and SiNx) from 8 to 200 nm were produced to achieve an effective balance between the lubricious phase diffusion control and the adequate formation of the low friction tribo-layers. Results showed that a dual-phase of fcc-Mo2N and fcc-Ag co-existed in Mo2N-Ag layers, while the SiNx layer exhibited an amorphous character. Both room temperature (RT) lubricant and wear-resistance properties of the films were improved by increasing Λ from 8 to 64 nm, while a further increase of Λ degraded the wear-resistance properties. The multilayer film at Λ = 64 nm exhibited an excellent RT-500 °C temperature-cycling tribological properties. Mechanical properties and the synergistic effect of both modulation layers were the cause for the improvement of the tribological properties.

Infected Ixodes scapularis Nymphs Maintained in Prolonged Questing under Optimal Environmental Conditions for One Year Can Transmit Borrelia burgdorferi (Borreliella genus novum) to Uninfected Hosts.

ABSTRACTIn recent decades, Lyme disease has been expanding to previous nonendemic areas. We hypothesized that infected I. scapularis nymphs that retain host-seeking behavior under optimal environmental conditions are fit to fulfil their transmission role in the enzootic cycle of B. burgdorferi. We produced nymphal ticks in the laboratory under controlled temperature (22–25°C), humidity (80–90%), and natural daylight cycle conditions to allow them to retain host-seeking/questing behavior for 1 year. We then analyzed differences in B. burgdorferi infection prevalence in questing and diapause nymphs at 6 weeks postmolting (prime questing) as well as differences in infection prevalence of questing nymphs maintained under prolonged environmental induced questing over 12 months (prolonged questing). Lastly, we analyzed the fitness of nymphal ticks subjected to prolonged questing in transmission of B. burgdorferi to naive mice over the course of the year. B. burgdorferi infected unfed I. scapularis nymphal ticks maintained under optimal environmental conditions in the laboratory not only survived for a year in a developmental state of prolonged questing (host-seeking), but they retained an infection prevalence sufficient to effectively fulfil transmission of B. burgdorferi to uninfected mice after tick challenge. Our study is important for understanding and modeling Lyme disease expansion into former nonendemic regions due to climate change.IMPORTANCE Lyme disease is rapidly spreading from its usual endemic areas in the Northeast, Midwest, and Midatlantic states into neighboring areas, which could be due to changing climate patterns. Our study shows that unfed I. scapularis nymphal ticks kept under optimal environmental conditions in the laboratory survived for a year while exhibiting aggressive host-seeking behavior, and they maintained a B. burgdorferi infection prevalence which was sufficient to infect naive reservoir hosts after tick challenge. Our study raises important questions regarding prolonged survival of B. burgdorferi infected host-seeking nymphal I. scapularis ticks that can potentially increase the risk of Lyme disease incidence, if conditions of temperature and humidity become amenable to the enzootic cycle of B. burgdorferi in regions currently classified as nonendemic.

Review of the spectrally selective (CSP) absorber coatings, suitable for use in SHIP

A key component in the conversion process of concentrated solar power (CSP) into thermal energy is a solar absorber coating. Many experimental and simulated coatings for various substrates for CSP water/steam or molten salt absorbers have been developed. The main challenges today remain in the selection of a low-cost and effective fabrication method, appropriate for industrial production, and assessment of the degradation rate and service life of these coatings, which affect the efficiency of the plant and the LCOE. In this article, we review different types of mid- (100 < T < 400 °C) and high-temperature (>400 °C) absorber coatings and their fabrication methods. The emphasis is on the solar absorptance, thermal emittance and the long-term (>10 years) thermal stability of the coatings. Spectral selectivity of the coatings, which is more difficult and expensive than other means, was proven to be essential for a low-to-mid temperature range and low concentration ratios, yet for high temperatures and high concentration ratios, high solar absorptive coatings can achieve the same or even better performance than spectral selective ones. Important factors for an efficient CSP absorber are compatibility of the coating and substrate under cyclic temperature conditions and high heat transfer rate to a heat transfer medium.

Water exchange across a subgrade-GCL interface as impacted by polymers and environmental conditions

This paper examines the hydration behaviour of polymer enhanced geosynthetic clay liners (GCLs) under both isothermal conditions and diurnal cyclical temperatures as recorded at a Melbourne landfill site. The diurnal temperature cycles introduced thermal gradients, which induced water movement downwards into the subgrade. It was found that the bulk of the thermal and hydraulic effects occurred within the upper 50 mm of the subgrade layer. Compared to isothermal conditions, diurnal temperature cycling's main effect was to suppress GCL hydration. Thermal gradients induced capillary breaks, and GCL hydration was thus limited to vapour phase hydration from the subgrade, which restricted the gravimetric water content of the GCLs to <30%. The hydration process at the interface was observed to gradually return to isothermal condition hydration levels once the temperature cycle conditions were removed. While the polymer's presence ensures the adsorption of more water, it also renders GCLs more sensitive to the effects of temperature. This study provides insights on the hydration behaviour of uncovered GCLs in field applications and the impact that diurnal temperature cycles can have on GCL hydration in a Mediterranean type climate.

Influence of Robust Drain Openings and Insulation Standoffs on Corrosion Under Insulation Behavior of Carbon Steel

Corrosion under insulation (CUI) is among the key concerns for the integrity of process equipment and pipelines. Various measures to detect and fix the damages from CUI pose significant maintenance expenditures in hydrocarbons processing facilities. The key reason behind CUI is the limitation of thermal insulations to absorb the moisture and soak the underneath metal from wicking action. Other than CUI, trapped moisture in the soaked thermal insulations causes heat loss from process systems, thereby posing the risk of additional damage mechanisms and increased operating expenditures. This study addresses the impact of robust drain openings and insulation standoffs on the CUI rate of carbon steel under four different testing conditions, namely isothermal wet, isothermal wet-dry, cyclic wet, and cyclic wet-dry, respectively. Corroded specimens were further characterized using surface topography and scanning electron microscope. The impacts of temperature and moisture cycling on the corrosion attributes were also characterized using the linear polarization resistance method followed by an investigation of corrosion modes via optical microscopy. Insulation standoffs in conjunction with robust drain opening resulted in the lowest corrosion rate. With insulation standoffs and drain openings, the cyclic temperature conditions caused higher metal loss than that in isothermal conditions.

Fabrication and Reliability Assessment of Cu Pillar Microbumps With Printed Polymer Cores

Abstract Cu pillar microbumps with polymer cores have been demonstrated to effectively reduce thermomechanical stress and improve joint reliability. Fabricating polymer cores by a printing approach was proposed to overcome the limitations in conventional fabrication process. Cylindrical polymer cores with diameter of 20 μm and height of 30 μm were successfully printed. Surface metallization was subsequently applied on the printed polymer cores and Cu pillar microbumps with printed polymer cores with diameter of 35 μm and height of 35 μm were eventually achieved. To study the reliability performance of the interconnect joints made of Cu pillar microbumps with printed polymer cores, flip-chip bonding technology was successfully introduced and the interconnect joints between a designed bismaleimide triazine (BT) substrate and a silicon chip were formed. The interconnect joints made of conventional Cu pillars with identical dimensions were prepared for comparison. The reliability performance of the joints was investigated under temperature cycling condition and drop condition, respectively. Printed polymer cores increased the characteristic life by 32% in a temperature cycling test (0–100 °C), while the drop test showed that printed polymer cores increased the characteristic life by four times due to the extra compliance provided by the printed polymer cores. It can be concluded that Cu pillar microbumps with printed polymer cores can effectively reduce stress and improve joint reliability.