High Temperature Thermal Cycling Research Articles

Failure mechanism of Ag-4Pd alloy wire bonded on Al-Si metallization under high temperature storage and thermal cycle tests in corrosive environments

This study investigated the failure mechanism of Ag-4Pd wire bonded on Al metallization under chlorine corrosive environments after high temperature storage tests (HTST) and thermal cycle tests (TCT). Results show that as-bonded samples encountered the fastest failure, caused by corrosion of Al metallization accelerated by galvanic corrosion. For HTST samples, the intermetallic compound (IMC) layer was corroded and separated into the upper layer of Ag2Al and Ag3Al and the lower layer of Ag3Al2. The non-continuous Ag3Al2 IMC layers in TCT samples can act as a barrier to inhibit the galvanic corrosion and effectively retard the corrosion rate of Al metallization.

High-temperature mechanical properties and thermal cycling stability of Al-50Si alloy for electronic packaging

With the rapid development of electronics industry, there is an increasing demand for high performance electronic packaging materials. Furthermore, the high-temperature performance and thermal cycling stability are required owing to the harsher service environment. In this work, Al-50Si alloy was prepared via rapid solidification/powder metallurgy technique, and the tensile properties at elevated temperature and the thermo-physical properties after thermal cycling were investigated. The results show that the tensile strength decreases gradually with the increase in the environmental temperature. Whereas, pullout of the Si particle is seldom observed in the specimens at elevated temperatures owing to the strong interfacial bonding. With the progress of thermal cycling, the coefficient of thermal expansion (CTE) is stable, but the plastic strain increases rapidly at the initial stage. However, the thermal conductivity decreases significantly with the increase in the temperature or the number of thermal cycles. This phenomenon is mainly ascribed to the CTE mismatch between the Al matrix and Si phase. The variation of CTE and thermal conductivity is discussed in terms of thermally induced stress.

Lifetime of power electronics interconnections in accelerated test conditions: High temperature storage and thermal cycling

We investigate the effect of three testing conditions (thermal shock, Rapid Temperature Change – RTC – and high temperature storage) on the interconnects of a power electronic module. In particular, the mechanical strength of thick aluminium wirebonds is investigated and shows that while it is not affected by storage at 230°C, it is much more sensitive to thermal cycling. Shock tests are found to be especially severe, despite having a smaller temperature swing than RTC. Regarding the die attach, no noticeable reduction in mechanical strength is found, regardless of the ageing conditions, and despite clear micro-structural evolutions.

Microstructure and Plastic Deformation of the As-Welded Invar Fusion Zones

The as-welded Invar fusion zones were fabricated between cemented carbides and carbon steel using a Fe-Ni Invar interlayer and laser welding method. Three regions in the as-welded Invar fusion zones were defined to compare microstructures, and these were characterized and confirmed by scanning electron microscopy and X-ray diffractometry. The structure and plastic deformation mechanism for initial Invar Fe-Ni alloys and the as-welded Invar fusion zones are discussed. (1) After undergoing high-temperature thermal cycles, the microstructure of the as-welded Invar fusion zones contains γ-(Fe, Ni) solid solution (nickel dissolving in γ-Fe) with a face-centered cubic (fcc) crystal structure and mixed carbides (eutectic colonies, mixed carbides between two adjacent grains). The mixed carbides exhibited larger, coarser eutectic microstructures with a decrease in welding speed and an increase in heat input. (2) The structure of the initial Invar and the as-welded Invar is face-centered cubic γ-(Fe, Ni). (3) The as-welded Invar has a larger plastic deformation than initial Invar with an increase in local strain field and dislocation density. Slip deformation is propagated along the (111) plane. This finding helps us to understand microstructure and the formation of dislocation and plastic deformation when the Invar Fe-Ni alloy undergoes a high-temperature process.

Microstructural Characteristics of Nickel Alloy Grade 600 After High-Temperature Thermal Cycle

Microstructural Characteristics of Nickel Alloy Grade 600 After High-Temperature Thermal Cycle

Ghost microstructure evolution and identification in the coarse grain heat affected zone of 2.25Cr-1Mo-V-Ti steel using tint etching

Microstructural characteristics of the CGHAZ (coarse grained heat affected zone) made of the 2.25Cr-1Mo-V-Ti material for the thermal power plant boiler tube were discussed using the technique of tint etching. To conduct the micro structural characterization, the sample on which CGHAZ was produced by using a high temperature thermal cycle simulator, Gleeble 3500 equipment was used for comparative analyses using the existing Nital etching (ASTM E407-74) and the alkaline etching (ASTM E40785). The latter was used to observe a specific phase. For the microstructure on which the alkaline etching was experimented, the shape of a black strip (Ghost microstructure) in a few microns was observed, which was not observed from the Nital etching. It was found from the phase identifications based EPMA, EBSD and TEM experiments that the image of the black strip in a few microns represented the alpha phase in which C, Cr and Mo became segregated. In addition, it was verified that austenite and M23C6 phase were present around the segregated zone. Based on such results, the mechanism by which the image of the black strip in a few microns was formed at the CGHAZ. In this study, we have investigated the mechanism of the appeared black strip in the CGHAZ.

Properties and long-term behavior of nanoparticle based inkjet printed strain gauges

Strain sensors based on the resistive principle have been developed and produced by inkjet printing of nanostructured materials. Miniaturized sensor structures with grid line widths of around 75 µm and overall dimensions of 6.7 mm × 6.4 mm were successfully realized on Polyimid foils. The influence of the surface properties and the silver nanoparticle ink on the printed strain gauges was examined. With adequate densification of the printed nanoparticle containing structures, gauge factors of around 3.9 or higher were achieved. Results of reliability tests under environmental stress showed the need for a protective coatings to ensure stable long-term behavior. With adequate coatings, stable sensors are possible under a wide range of environmental conditions, such as high temperature storage or thermal cycling.

Thermally stable pn-junctions based on a single transparent perovskite semiconductor BaSnO3

We report p-doping of the BaSnO3 (BSO) by replacing Ba with K. The activation energy of K-dopants is estimated to be about 0.5 eV. We have fabricated pn junctions by using K-doped BSO as a p-type and La-doped BSO as an n-type semiconductor. I-V characteristics of these devices exhibit an ideal rectifying behavior of pn junctions with the ideality factor between 1 and 2, implying high integrity of the BSO materials. Moreover, the junction properties are found to be very stable after repeated high-bias and high-temperature thermal cycling, demonstrating a large potential for optoelectronic functions.

Low temperature high density plasma nitriding of stainless steel molds for stamping of oxide glasses

Various kinds of stainless steels have been widely utilized as a die for mold- and direct-stamping processes of optical oxide glasses. Since they suffered from high temperature transients and thermal cycles in practice, they must be surface-treated by dry and wet coatings, or, by plasma nitriding. Martensitic stainless steel mold was first wet plated by the nickel phosphate (NiP), which was unstable at the high temperature stamping condition; and, was easy to crystalize or to fracture by itself. This issue of nuisance significantly lowered the productivity in fabrication of optical oxide-glass elements. In the present paper, the stainless steel mold was surface-treated by the low-temperature plasma nitriding. The nitrided layer by this surface modification had higher nitrogen solute content than 4 mass%; the maximum solid-solubility of nitrogen is usually 0.1 mass% in the equilibrium phase diagram. Owing to this solid-solution with high nitrogen concentration, the nitrided layer had high hardness over 1400 HV within its thickness of 50 μm without any formation of nitrides after plasma nitriding at 693 K for 14.4 ks. This plasma-nitrided mold was utilized for mold-stamping of two colored oxide glass plates at 833 K; these plates were successfully deformed and joined into a single glass plate by this stamping without adhesion or galling of oxide glasses onto the nitrided mold surface.

In-situ high temperature stress analysis of Ti(C,N) coatings on functionally graded cemented carbides by energy dispersive synchrotron X-ray diffraction

We report on in-situ high temperature X-ray thermal stress analysis of chemically graded Ti(C,N) coatings deposited on functionally graded cemented carbide substrates by chemical vapor deposition. The in-situ analyses were performed by energy dispersive X-ray diffraction using synchrotron radiation. The samples were subjected to one individual thermal cycle from room temperature to 800°C and cooled down to room temperature again. The stresses were determined using the sin2ψ method in the Ψ geometry combined with scattering vector measurements in order to unravel the compositional influences on the lattice strain distributions. It was found that the Ti(C,N) thin film presents a cycling residual stress behavior (tensile–compressive–tensile) connected to the temperature cycle. If top-blasting is applied on the thin film layer after the coating process, compressive stresses are generated. These compressive stresses induced by top-blasting are partially released after the high temperature thermal cycle. The functionalization of the cemented carbide substrate influences the level of stresses developed in the coating. The stress behavior as a function of temperature is discussed with the support of finite element modeling by introducing a bi-linear plasticity model to calculate strain relationships which is in agreement with the synchrotron measurements.

The Effect of High Temperature Thermal Cycling on Near-Surface Sulphur Partitioning in Gamma and Gamma Prime Phases and Its Implications on Sulphur Segregation in Coated Ni-Base Superalloys

Secondary ion mass spectrometry (SIMS) was used to study the near-surface segregation of sulphur during; (a) the thermal processing stages (diffusion annealing after application of Pt bond coat and after secondary ageing following subsequent deposition of the Y2O3-stabilised ZrO2 top coat) and (b) thermal cycling in the Ni-base superalloy, CMSX4. In the thermal processing stages, an increased segregation of sulphur was observed within the upper regions of the Pt bond coat after diffusion annealing, while following secondary ageing, the sulphur segregation in this layer became heterogeneous with discrete pockets of enrichment (≫1 ppm) and regions of depletion (≪1 ppm). During thermal cycling, partitioning of sulphur occurred to the Pt-enriched γ′ region characterised by the finger-like morphology, while examination of TBC spalled specimens showed significant depletion of sulphur within the substrate in the vicinity of the surface. The reservoir for sulphur-depletion within the substrate was definitively identified as the Pt-enriched γ′ region. A quantitative method for the calculation of sulphur-segregation at the surface in terms of mono-layers is presented.

Double-Sided Transferred Carbon Nanotube Arrays for Improved Thermal Interface Materials

Recently, much attention has been given to reducing the thermal resistance attributed to thermal interface materials (TIMs) in electronic devices, which contribute significantly to the overall package thermal resistance. Thermal transport measured experimentally through several vertically aligned carbon nanotube (VACNT) array TIMs anchored to copper and silicon substrates is considered. A steady-state infrared (IR) microscopy experimental setup was designed and utilized to measure the cross-plane total thermal resistance of VACNT TIMs. Overall thermal resistance for the anchored arrays ranged from 4 to 50 mm2 KW-1. These values are comparable to the best current TIMs used for microelectronic packaging. Furthermore, thermal stability after prolonged exposure to a high-temperature environment and thermal cycling tests shows limited deterioration for an array anchored using a silver-loaded thermal conductive adhesive (TCA).

Hysteresis phenomena of the two dimensional electron gas density in lattice-matched InAlN/GaN heterostructures

High-temperature transport properties in high-mobility lattice-matched InAlN/GaN heterostructures have been investigated. An interesting hysteresis phenomenon of the two dimensional electron gas (2DEG) density is observed in the temperature-dependent Hall measurements. After high-temperature thermal cycles treatment, the reduction of the 2DEG density is observed, which is more serious in thinner InAlN barrier samples. This reduction can then be recovered by light illumination. We attribute these behaviors to the shallow trap states with energy level above the Fermi level in the GaN buffer layer. The electrons in the 2DEG are thermal-excited when temperature is increased and then trapped by these shallow trap states in the buffer layer, resulting in the reduction and hysteresis phenomenon of their density. Three trap states are observed in the GaN buffer layer and CGa may be one of the candidates responsible for the observed behaviors. Our results provide an alternative approach to assess the quality of InAlN/GaN heterostructures for applications in high-temperature electronic devices.

CFY-Stack Technology: The Next Design

The stack concept of electrolyte supported cells (ESC) is applicable for both, solid oxide fuel cells as well as solid oxide electrolysis cells. High power densities and efficiencies comparable to anode supported cells (ASC) can be achieved, however, for the stack design presented in this paper, in unison with high robustness. Incorporating an electrolyte made of fully scandia stabilized zirconia paired with chromium-based CFY (Cr5FeY) interconnects of matched CTE (coefficient of thermal expansion), a feasible stack concept was created with the focus on long-term stability in regard to high temperature corrosion and thermal cycling. Stack data of more than 20.000 hours of a single stack is presented in addition to industrial onward development of the stack design. Using the same material combinations and the same footprint as for the MK351-design, the newly developed MK352-design was simulated, drafted and produced and allows for easier stack setup and system integration. Minor changes in interconnect (IC) design enable lower pressure drops over the stack, which, paired with enhanced tolerance chains lead to enhanced stack performance, especially in regard to thermal cycling. Cross-checked, test results for the MK352-stack are in good agreement with the simulation.

CFY-Stack Technology: The Next Design

The stack concept of electrolyte supported cells is applicable for both, SOFC as well as SOEC. High power densities and efficiencies comparable to stacks based on anode supported cells can be achieved, however, in unison with higher robustness. Incorporating an electrolyte made of fully scandia-stabilized zirconia paired with chromium-base CFY interconnects of matched CTEs, a feasible stack concept was created with the focus on long-term stability in regard to high temperature corrosion and thermal cycling. Onward development of the stack design as well as stack data of more than 20,000 hours of a single stack are presented. Using the same material combinations and the same footprint as for the MK351-design, the newly developed MK352-design allows for easier stack assembling and system integration. Slight modifications in interconnect design enable lower pressure drops over the stack, which, paired with enhanced tolerance chains lead to enhanced stack performance, especially in regard to system cycling.

Structural materialization of stainless steel molds and dies by the low temperature high density plasma nitriding

Various kinds of stainless steels have been widely utilized as a mold substrate material for injection molding and as a die for mold-stamping and direct stamping processes. Since they suffered from high temperature transients and thermal cycles in practice, they must be surface-treated by dry and wet coatings, or, by plasma nitriding. Martensitic stainless steel mold was first wet plated by the nickel phosphate (NiP), which was unstable at the high temperature stamping condition; and, was easy to crystalize or to fracture by itself. This issue of nuisance significantly lowered the productivity in fabrication of optical elements at present. In the present paper, the stainless steel mold was surface-treated by the low-temperature plasma nitriding. The nitrided layer by this surface modification had higher nitrogen solute content than 4 mass%; the maximum solid-solubility of nitrogen is usually 0.1 mass% in the equilibrium phase diagram. Owing to this solid-solution with high nitrogen concentration, the nitrided layer had high hardness of 1400 Hv within its thickness of 40 μm without any formation of nitrides after 14.4 ks plasma nitriding at 693 K. This nitrogen solid-solution treated stainless steel had thermal resistivity even at the mold-stamping conditions up to 900 K.

Effect of Cu pad morphology on direct-Cu pillar formation in CMOS image sensors

We report the feasibility of forming Ni bumps directly on Cu pads in CMOS image sensor (CIS) logic elements formed by Cu wires with diameters of less than 65 nm. The direct Ni bump process proposed in this study simplifies the fabrication process and reduces costs by eliminating the need for Al pad process. In addition, this process can secure the margin of the final layer, enabling the realization of thin camera modules. In this study, we evaluated the effect of pad annealing on the direct formation of Ni bumps over Cu pads. The results suggest that the morphology of the Cu pad varies depending on the annealing sequence, and post-passivation annealing resulted in fewer defects than pad etch annealing. The shear stress of the Ni bumps was 57.77 mgf/m2, which is six times greater than the corresponding reference value. Furthermore, we evaluated the reliability of a chip with an anisotropic conductive film (ACF) and a non-conducting paste (NCP) by using high-temperature storage (HTS), thermal cycling (TC), and wet high-temperature storage (WHTS) reliability tests. The evaluation results suggest the absence of abnormalities in all samples. Open image in new window

Corrosion resistant polymer derived ceramic composite environmental barrier coatings

Corrosion resistant coatings are a promising solution to protect structural metals in harsh environments. Ceramic composite coatings made from polymer-derived ceramics are highly attractive due to the ease of their processing and the ability to work in various environments. This paper is focused on the performance of a TiSi 2 -filled SiOC ceramic composite coating system on 316 stainless steel (SS) substrates as a corrosion resistant coating. The best-performing quadruple-dip coatings were shown to be able to reduce the weight loss due to hot sulfuric acid (95+%, 104–107 °C) corrosion by 85% over a 30-day period. Coatings from the same system were also examined under 800 °C static (100 h) and cyclic (10 cycles) oxidation. Our results indicate that the coatings perform well under both conditions of prolonged high temperature oxidation and thermal cycling, suggesting the strong potential of this system as an environmental barrier coating (EBC).

Ultraviolet pulsed laser irradiation of multi-walled carbon nanotubes in nitrogen atmosphere

Laser irradiation of randomly oriented multi-walled carbon nanotube (MWCNT) networks has been carried out using a pulsed Nd:YAG UV laser in nitrogen gas environment. The evolution of the MWCNT morphology and structure as a function of laser fluence and number of accumulated laser pulses has been studied using electron microscopies and Raman spectroscopy. The observed changes are discussed and correlated with thermal simulations. The obtained results indicate that laser irradiation induces very fast, high temperature thermal cycles in MWCNTs which produce the formation of different nanocarbon forms, such as nanodiamonds. Premelting processes have been observed in localized sites by irradiation at low number of laser pulses and low fluence values. The accumulation of laser pulses and the increase in the fluence cause the full melting and amorphization of MWCNTs. The observed structural changes differ from that of conventional high temperature annealing treatments of MWCNTs.

High-Performance Light-Emitting Diodes Encapsulated with Silica-Filled Epoxy Materials

Packaging materials have a great impact on the performance and reliability of light-emitting diodes (LEDs). In this study, we have prepared high performance LED devices through encapsulating LEDs by epoxy materials incorporated with filler powders. A set of evaluation methods have also been established to characterize the reliability of LED devices. No delamination or internal cracking between packaging materials and lead frames has been found for the encapsulated high performance LED devices after the package saturation with moisture and subsequent exposure to high-temperature solder reflow and thermal cycling. Four kinds of inorganic silica fillers, namely, quartz, fused silica, cristobalite, and spherical silica, and one kind of organic filler, that is, spherical silicone powder, were incorporated into the epoxy packaging materials to compare their effects on performance of LED devices. The properties of epoxy packaging materials and LED devices were studied by differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), dynamic mechanical analysis (DMA), thermomechanical analyzer (TMA), ultravioletvisible spectrophotometer (UV-vis), scanning acoustic microscopy (SAM), and scanning electron microscopy (SEM). Except the spherical silicone powder filled epoxy materials, all the other filled systems showed lower equilibrium water sorption content and smaller water diffusion coefficient in both water sorption and moisture sorption tests. The coefficient of thermal expansion (CTE) values were also decreased with the addition of fillers, and the systems filled with quartz, fused, and filled with spherical silica gave the best performance, which exhibited the reduced CTE values both below and above Tg. The results of TGA essentially showed no difference between filled and unfilled systems. The glass transition temperature changed little for all the filled systems, except the one incorporated with spherical silicone. The modulus at room temperature increased with the addition of fillers. The light transmittance of filled epoxy materials varied with fillers after UV and thermal aging.