Microstructural Evolution of Transient Liquid Phase Sinter Joints in High Temperature Environmental Conditions

Power electronic systems have become a key component in the efficient generation, distribution, storage, and use of energy. This increasingly places power electronic systems in harsh environments under elevated stress conditions where, in many cases, their reliable operation is now mission critical. The semiconductor material conventionally used, silicon, possesses limited capability for high temperature applications due to its small bandgap. Power electronic components based on wide bandgap (WBG) semiconductors, such as SiC and GaN, can be operated reliably at higher temperatures. Furthermore, WBG devices have higher breakdown voltages and switching frequencies, rendering them more ideal switches and rectifiers for highefficiency as well as low-volume and low-weight systems. Yet, new packaging concepts are required to make use of the high temperature capability of power electronic systems based on WBG semiconductor devices. In this paper, a summary of the progress in the development and commercialization of wide bandgap power components and power electronic systems is given. The properties of SiC and GaN components are compared to those based on silicon. The shortcomings of conventional power electronic packaging technologies are analyzed, and alternatives introduced and compared. An overview of research is given on Transient Liquid Phase Sintering (TLPS), a promising interconnect technology for the manufacturing of WBG and high temperature power electronic systems. TLPS is a liquid-assisted sintering process during which a low melting temperature constituent melts, surrounds, and diffuses in a high melting temperature constituent. Intermetallic compounds with high melting temperatures are formed by liquid-solid diffusion. Interconnect systems can be processed at low temperatures but are capable of operating at the high melting temperatures of the intermetallic compound. Different process approaches are contrasted and material systems compared. Latest results of research on paste-based low temperature TLPS are presented. The pastes assessed are based on the Cu-Sn and Ni-Sn material systems. It is shown that joints formed by TLPS remain strong up to 600°C and exhibit softening temperatures far higher than conventional interconnect technologies. They show minimum creep and possess very limited voiding. The process does not require an inert or reducing atmosphere or vacuum and is compatible with standard reflow soldering equipment. It shows good wettability to common metallizations such as Cu, Ni, Ag, and ENIG. This attach technology shows the potential to enable reliable operation of wide bandgap power electronic systems under high stress conditions.

The increasing thermal demands in power electronic systems require the application of high temperature die attach materials. Transient Liquid Phase Sintered (TLPS) paste-based solder alloys have been demonstrated to effectively manage the thermal and mechanical load requirements of power modules. The microstructural features of these alloys provide interconnects with the necessary strength required to sustain high loads at high temperatures. To properly understand the influence of microstructure on mechanical behavior of these alloys, single lap shear experiments were performed on a TLPS system consisting of Copper and Tin particles (Cu-Sn). Nano-indentation measurements were performed on intermetallic phases of the TLPS, and the results obtained from lap shear testing and nano-indentation measurements are presented.

Interconnect materials for high operating temperature applications are becoming a limiting factor within the chain of materials. While materials such as capacitor dielectrics, semiconductor platforms (e.g. SiC), and baseplate materials (e.g. SiN composites) have paved a pathway to deploying electronics in high operating temperature applications, interconnect materials are a clearly identified weak link. As is often the case in advancements in technology, the materials technologies that were the bottlenecks to advancement give way to new solutions that create new bottlenecks in the material supply chain. Rather than a fluid march towards advancements in new frontiers in electronics, the high operating temperature sphere, like much of advanced electronic, suffers from a ‘slip-fault’ mode of development where advances occur in one segment while others lag behind creating drag on implementation. For high operating temperature applications the available interconnect solutions are becoming the jarring stop to the smooth tectonic shift. Current solutions are diverse: high-lead, gold-based, and nano-sintering and its hybrids, but none are ideal. Even disregarding he toxicity of lead and the ongoing limbo of its regulatory status, the operating temperatures of the high-lead solders are on the low end of the requirements for future harsh environment electronics applications; whereas, the gold and nano-based alternatives have significant cost barriers - either at from the constituent materials perspective or the required investment in new processes. There is also the concern about the assessment of the action of nanomaterials in the waste stream due to their fundamentally different surface reactivity in a variety of situations. Reliance on conventional, solder-type interconnection structures, regardless of composition, introduces the perennial problem of the growth of the interfacial phases due to the essentially unlimited volume of the bulk solder material. The changes in the interfacial structure with additional thermal work - as is provided by high operating temperature applications - creates an environment that is ripe for growth of a variety of failure mechanisms. These failure mechanisms are often related to the uncontrolled laminar growth of intermetallic phases at the interfaces and the mechanical characteristics of these intermetallic phases in comparison with the materials joined and the bulk constituent material of the solder. An alternative class of interconnect materials, transient liquid phase sintering (TLPS) pastes, introduce a joint microstructure that is homogeneous throughout. The interfacial metallurgical reactions with the solderable surfaces are fundamentally similar to those that occur throughout the bulk of the joint. A reactant metal is included in the composition. This reactant metal, most often copper, reacts with and converts the bulk tin in the bulk of the solder interconnect to alloy structures with melting points well above the operating temperatures currently contemplated. At the conclusion of the joining process, which is generally a near drop-in for existing solder reflow processes, there is no large source of unreacted metal (e.g. Sn) that can continue to drive major microstructural changes with the continued thermal work provided by the application environment. For this reason the joints are homogeneous and do not have the free reactants necessary to drive substantial changes in joint morphology during cycling and use conditions. In this paper, we will explore the differences between TLPS joints and solder-type joints with the anticipated thermal work that would be introduced in a high operating temperature environment.

There is a growing need within the electronics industry for interconnect materials that can meet higher processing and operating temperatures. The solidus to liquidus range of current tin (Sn) based solders and other lead (Pb) solders are narrower than traditional SnPb solders as the industry is moving to higher temperatures. Transient Liquid Phase Sintering (TLPS) is a technology that offers low processing temperatures while having high temperature capabilities but has had limited exposure outside of the Semiconductor industry. Results of mechanical testing as well as product environmental data is presented herein as TLPS is used as a mechanical and electrical interconnect for Multi-Layer Ceramic Capacitors (MLCC).

We performed 30Ni–70Sn (wt%) transient liquid phase sintering (TLPS) bonding with micro-sized Ni and Sn powders for high-temperature power applications. A Ni–Sn paste was fabricated and TLPS bonding was performed. We investigated the interfacial reactions, transformations into Ni3Sn4 intermetallic compound (IMC) phases, and joint strength in this study. The Ni–Sn TLPS bonding was an easy and simple process under a relatively low bonding temperature and short bonding time. After TLPS bonding, low melting point Sn element was completely consumed, and the bonded joint was composed of Ni3Sn4 IMCs and the remaining Ni particles. The Ni3Sn4 IMC joint formed with remaining Ni particles was very stable. All the Ni–Sn TLPS samples had high shear strengths of over 70 MPa, and the shear strength was approximately 32% higher than that of the conventional Sn–3.0Ag–0.5Cu solder joint. The Ni–Sn TLPS bonded joints in the present study were not brittle and exhibited superior adhesion strength. This suggests high applicability of the Ni–Sn TLPS bonding for high-temperature power electronic applications in future EV/HEV systems.

Anthocyanins are ubiquitously accumulated in diverse plant species and play crucial roles in plant development. In addition, anthocyanin pigmentation is associated with significant characteristics in the flowers and fruits of horticultural products. Notably, anthocyanin biosynthesis and storage are known to be affected by environmental factors. High ambient temperatures often suppress anthocyanin accumulation in flowers and fruits, raising concerns regarding the increase in atmospheric temperatures caused by global warming. Therefore, a comprehensive understanding of the mechanisms underlying the effects of high ambient temperatures on the regulation of anthocyanin biosynthesis and storage is necessary to maintain pigment quality and quantity of the products. In this review, we provide comprehensive information on the role of high-temperature-related signaling pathways in the regulation of anthocyanin biosynthesis. The expression of genes involved in anthocyanin biosynthesis is mainly regulated by R2R3-MYB activators, R2R3-MYB repressors, and R3-MYB negative regulators. The expression levels of R2R3-MYB activators decrease under high-temperature conditions, as observed in many flowers and fruits. The upregulation of R2R3-MYB repressors and R3-MYB negative regulators has also been demonstrated in some plant species under high-temperature conditions. The high-temperature-related signaling pathways have been evaluated mainly in the vegetative organs of Arabidopsis and apple fruits. In these organs, light strongly influences anthocyanin biosynthesis in addition to ambient temperatures. The CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1)-ELONGATED HYPOCOTYL 5 (HY5) module and B-box proteins upregulate the R2R3-MYB activators under light conditions, while they downregulate the R2R3-MYB activators under high-temperature conditions. However, the pathways that transduce high-temperature signals in flowers are poorly understood. Unlike in fruits and vegetative organs, light exerts relatively small effects on anthocyanin pigmentation in flowers, suggesting that the COP1-HY5 module-independent pathway could be responsible for the regulation of R2R3-MYB regulators in many flowers. Further research to clarify the related signaling pathways in flowers is needed to find solutions to overcome the problem of color fading caused by high ambient temperatures. In addition, exceptional cases have been reported in which high temperatures do not inhibit or enhance the anthocyanin pigmentation of flowers. Such species can prove helpful in elucidating the mechanisms underlying temperature-mediated regulation of anthocyanin pigmentation and as parental materials for crossbreeding.

Foam injection has been promoted as a reliable method for improving the sweep efficiency in heterogeneous carbonate reservoirs by modifying the properties of the injected gas and hence, providing mobility control effect. However, the conditions of the Middle Eastern carbonate reservoirs are quite detrimental to foam performance, leading to unoptimized mobility control. This challenge has motivated the improvement and development of different foaming agent formulations that can withstand the harsh conditions in carbonate reservoirs of high temperature and high salinity. In this study, the effect of different amphoteric and switchable surfactants on bulk foam performance were investigated and later the optimum formulation was evaluated in carbonate porous media for EOR under high salinity and temperature conditions. For this purpose, the solutions containing different commercial amphoteric and amine-based switchable surfactants were prepared in high salinity brine (20 wt%) at high temperature conditions (80 °C). Initial screening was performed by conducting series of foamability and foam stability tests at high temperature. Foam generation and endurance were also investigated in the presence of crude oil. Foam performance was evaluated in carbonate core samples under different foam qualities and at reservoir conditions. After selecting the optimal foam quality for effective foam generation, the oil recovery experiment was then performed to recover the remaining oil after secondary N2-gas flood. The results from bulk foam experiments demonstrated the superior properties of betaine-based surfactant (B-1235), in which the highest foam generation and foam stability performance were achieved. Foam endurance of B-1235 was also found comparable to the foam produced by switchable diamine (DTTM) surfactant; however, DTTM surfactant showed poorer foamability performance. In the presence of crude oil, B-1235 surfactant was able to maintain the foam properties, compared to other tested surfactants. The optimum concentrations for B-1235 in the absence and presence of crude oil were found to be 0.25 wt% and 0.5 wt%, respectively. The injection of foam stabilized by the B-1235 was able to pronouncedly increase the mobility reduction factor (MRF) at all the tested foam qualities under high-pressure and high-temperature conditions. Coreflood investigations indicated an optimal foam quality at 70% for all tested surfactant concentrations. The cumulative oil recovery after foam injection was found to be 67%, including 25% tertiary incremental oil recovery by foam flooding. The overall performance of the tested betaine-based surfactant is promising as an effective mobility control during foam EOR process and promotes further application in difficult Middle Eastern carbonate reservoir conditions.

Reaction and sintering mechanisms of mullite in the systems cristobalite/α-Al 2O 3 and amorphous SiO 2/α-Al 2O 3

Propane Dehydrogenation on Single-Site [PtZn4] Intermetallic Catalysts

A number of industries are developing new product-lines with innovative electronics packages that require low thermal resistance and high temperature stability, including hybrid electric vehicles, concentrator photovoltaic and wide bandgap RF amplifiers. One of the largest obstacles in the design and manufacture is the thermal management of the devices. Localized heat generation is the characteristic of the semiconductor chips used in these devices. For high power applications the thermal impedance of the die attach layer can play significant role in the thermal management and the operating temperature. Therefore, one would like to use the highest thermal conductivity and lowest thermal resistance die attach material that is capable for high volume manufacturing. In a typical electronic packaging process, chips are attached to substrates and electrically connected before they are encapsulated or sealed for protection. The attachment and electrical interconnections provide the chip with an infrastructure for the flow of electrical signals, mechanical support and heat removal. The die attach materials <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(1)</sup> used in the packaging of high performance power semiconductors are required to have high thermal conductivity. Lead solders, eutectic gold-tin, transient liquid phase sintering (TLPS) pastes <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(2)</sup> and nano-silver sintering technology <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(3)</sup> are typical materials used for the die attachment of power semiconductor. This paper will introduce a new die attach material using Hybrid Silver Sintering Technology (HSST).

Guvermectin is a recently discovered microbial N9-glucoside cytokinin compound extracted from Streptomyces sanjiangensis NEAU6. Although some research has reported that N9-glucoside cytokinin compounds do not have the activity of cytokinin, it has been noted that guvermectin can promote growth and antifungal activity in Arabidopsis. Maize is an important food crop in the world and exploring the effect of guvermectin on this crop could help its cultivation in regions with adverse environmental conditions such as a high temperature. Here, we investigated the effects of guvermectin seed soaking treatment on the growth of maize at the seedlings stage and its yield attributes with different temperature stresses. The maize (cv. Zhengdan 958) with guvermectin seed soaking treatment were in two systems: paper roll culture and field conditions. Guvermectin seed soaking treated plants had increased plant height, root length, and mesocotyl length at the seedlings stage, and spike weight at maturity in the field. But only root length was increased at the paper roll culture by guvermectin seed soaking treatment. Guvermectin seed soaking treatment reduced the adverse effects on maize seedling when grow at a high temperature. Further experiments showed that, in high temperature conditions, guvermectin treatment promoted the accumulation of heat shock protein (HSP) 17.0, HSP 17.4 and HSP 17.9 in maize roots. Comparative transcriptomic profiling showed there were 33 common differentially expressed genes (DEGs) in guvermectin treated plants under high temperature and room temperature conditions. The DEGs suggested that guvermectin treatment led to the differential modulation of several transcripts mainly related with plant defense, stress response, and terpenoid biosynthesis. Taken together, these results suggested that the guvermectin treatment promoted the growth and tolerance of high temperature stresses, possibly by activation of related pathways. These results show that guvermectin is a novel plant growth regulator and could be developed as an application to maize seeds to promote growth in high temperature environments.

Microencapsulation of high temperature metallic phase change materials with SiCN shell

Development of deep water oil reservoirs in the Gulf of Mexico may encounter conditions where the flowline product temperatures approach 177°C (350°F), water depths range to 3000 m (10,000 ft), and tie-back distances up to 40 miles are presently being considered. These high flowline temperatures, water depths and distances, present real challenges to the design of flowlines. The objective of this paper is to present the design considerations and challenges of designing for extra high pressure high temperature (XHPHT) conditions. For such conditions, a pipe-in-pipe (PIP) flowline system with thermal expansion management, and a limit state-based design are viable solutions. This paper is split into three main parts and covers (i) design challenges and how they are overcome, (ii) finite element analysis design methods, and (iii) qualification testing of PIP components. The first section presents the main design issues, and challenges, of designing flowlines for deepwater and high-temperature conditions. The paper discusses aspects of controlling the large axial loads, such as thermal expansion management using buckle initiators and end constraints for flowlines, and presents current methods. The second section describes the use of advanced finite element analysis (FEA) tools for the design and simulation of PIP systems, and presents local and global FEA models, using ABAQUS, to investigate the limit state design of XHPHT flowlines. A 3-D helical response of the inner pipe subjected to high temperature, and the sequential reeling and lateral buckling of flowlines is also discussed. The final section of the paper describes the qualification testing to be undertaken on PIP components to ensure structural integrity and long-term thermal and structural performance. Qualification testing for PIP components for 177°C (350°F) service is discussed, and includes the testing of centralizers, waterstop seals, thermal insulation and loadshares. This paper is based on both theoretical and practical research work.

Impact of thermal aging on the intermetallic compound particle size and mechanical properties of lead free solder for green electronics

The degradation behavior of SiR for the cable insulation by accelerated thermal and radiation ageing was studied and the degradation mechanism was proposed. The degradation was observed by the change of tensile properties, the distribution of crosslinking, and the change of weight. The chemical reaction under the both ageing in oxidation conditions was crosslinking and the oxidation mechanism was found to be the same between thermal and radiation ageing. The yield of crosslinking was proportional to the ageing time and also the dose. The effect of irradiation temperature on oxidation was accelerated with an increase of temperature above around 120°C, which might be due to the specific radiation chemical reactions. Therefore, the degradation by simultaneous ageing at higher temperatures above 155°C was much higher than that for sequential ageing, such as irradiation followed by thermal ageing or thermal ageing followed irradiation. At a high temperature, the degradation by thermal ageing under vacuum (without oxidation) was more progressed than that for the ageing in air (with oxidation). The reason was assumed to be the thermal decomposition of crosslinks between SiR molecules formed by the chemical crosslinking agent. The hardness (Shore hardness) reflected well the degradation of the SiR material for any ageing conditions.