Strength reliability of 3D low temperature co-fired multilayer ceramics under biaxial loading

Low temperature co-fired ceramics (LTCCs) are multilayered ceramic based components, which can be used as high precision electronic devices in highly loaded environments. In many applications, LTCC end components are exposed to mechanical stresses, which may yield different types of failure coming from different locations, thus decreasing the mechanical reliability of the device. The aim of this work is to assess the mechanical strength of LTCC parts and investigate the influence of the metal internal structure (supporting the maximum load) on the local fracture response. Strength of different positions (e.g. near vias, metal-pads, ceramic layers) has been measured under biaxial loading and compared with a reference bulk LTCC. The strength results were interpreted in the framework of Weibull theory. Fractographic analyses revealed a significant effect of the first metallisation layer below the tensile surface on the strength reliability of the structure, which should be considered to optimise LTCC designs.     

Printable resistors in LTCC systems

Printable resistors in LTCC technology offer some advantages in comparison with discrete components, such as the increased power handling and reliability. As the size of chip resistors decreases, also the size of printed resistors has to be reduced. For optimizing high-frequency performance the size, i.e. width in particular, has to match the width of the transmission lines. In this study the effects of different resistor dimensions and processing parameters have been analyzed. The experimental work has been made with Du Pont 951 and Ferro A6-S LTCC systems. By optimizing the processing, the resistance tolerances smaller than ±12% were achieved.     

Effect of Metallization on the Lifetime Prediction of Mechanically Stressed Low-Temperature Co-Fired Ceramics Multilayers

Multilayer ceramics based on Low-Temperature Co-fired Ceramics (LTCC) are gaining increasing interest in the manufacturing of high-integrated devices for microelectronic and sensor applications. In many applications the parts are exposed to mechanical stresses, which is an important issue regarding the reliability of the device. To predict the lifetime of LTCC multilayer devices, and to extend their application range, basic mechanical data of this material are needed. In this paper metallized LTCC multilayers are investigated concerning their flexural strength, crack growth rate, and lifetime prediction. The results show that the electronic layout concerning the location of vias and metallization has a strong influence on the reliability and lifetime prediction of such co-fired LTCC devices. Mass flow sensors for the measurement of injected fuel quantities, which were fabricated on the basis of LTCC and which are exposed to a stress level of 100 MPa, achieve sufficient lifetimes. Therefore, LTCC is an interesting material to fabricate devices, in which LTCC fulfils the requirements of a functional and structural material.     

Advanced polyimide materials: Syntheses, physical properties and applications

Polyimides rank among the most heat-resistant polymers and are widely used in high temperature plastics, adhesives, dielectrics, photoresists, nonlinear optical materials, membrane materials for separation, and Langmuir-Blodgett (LB) films, among others. Additionally, polyimides are used in a diverse range of applications, including the fields of aerospace, defense, and opto-electronics; they are also used in liquid crystal alignments, composites, electroluminescent devices, electrochromic materials, polymer electrolyte fuel cells, polymer memories, fiber optics, etc. Polyimides derived from monomers with noncoplanar (kink, spiro, and cardo structures), cyclic aliphatic, bulky, fluorinated, hetero, carbazole, perylene, chiral, non-linear optical and unsymmetrical structures have been described. The syntheses of various monomers, including diamines and dianhydrides that have been used to make novel polyimides with unique properties, are reported in this review. Polyimides, with tailored functional groups and dendritic structures have allowed researchers to tune the properties and applications of this important family of high-temperature polymers. The synthesis, physical properties and applications of advanced polyimide materials are described.     

The origin of interfacial delamination in Au/ceramic cofired LTCC structure

The interfacial delamination of electrode/ceramic multilayer structure will seriously damage the reliability of low temperature co-fired ceramic (LTCC) module in practical applications. In this work, three kinds of glasses employed in Au electrode are designed and prepared to study the abnormal expansion and delamination process in the Au/ceramic LTCC multilayer structure. The interfacial delamination in the co-fired structure is found to be attributed to the abnormal expansion of glass in respect to Au electrode at high temperature, which is originated from the enlarged closed pores during the co-firing process. This conclusion is further confirmed by co-firing the sample in a low-pressure condition. The mechanism and elimination of interfacial delamination here provides a feasible solution for the design of novel glasses in Au electrode for LTCC applications.     

Fabrication of a Multilayered Low-Temperature Cofired Ceramic Micro-Plasma-Generating Device

Plasma technology is currently being used in innumerable industrial applications. Some of the common uses of this technology include surface cleaning and treatment, sputtering and etching of semiconductor devices, excitation source for chemical analyses, cutting, environmental cleanup, sterilization, and phototherapy. The harsh conditions that these devices must endure require robust refractory materials systems for their fabrication and reliability. Low-temperature cofired ceramic (LTCC) material systems provide a durable and cost-effective platform for the manufacture of such devices, and allow for possible integration into meso-scale microsystems. Our designs are based on RF microstriplines that capacitively couple and ionize small gas discharge sites over the top electrode. In this paper, we have built several iterations of this micro-plasma generating device using LTCC material systems. The impact of electrode ink selection and processing, lamination methods, dielectric layer thickness, and electrode design has been investigated. Several micro-plasma-generating devices were then evaluated for power requirements, output stability, and long-term reliability.     

Adhesives,syntactics and laminating resins for aerospace repair and maintenance applications from Ciba Specialty Chemicals

Ciba Specialty Chemicals, Performance Polymers Division, has been a leading supplier of materials to the aerospace industry for the fabrication, repair and assembly of interior and exterior aircraft components for many year. Araldite^®, Epibond^® and Epocast^® epoxy adhesives, syntactics and laminating resins in addition to Uralane^®, polyurethane adhesives have long been associated with quality, reliability and innovative chemistry. The majority of these systems are qualified to aircraft manufacturer’s specifications and are included as approved repair materials in structural repair manuals and serivce bulletins. Many of the adhesives, syntactics and laminating resins are self-extinguishing and exhibit the low flame, smoke and toxicity (FST) characteristics required to comply with industry legislation such as FAR (Federal Aviation Regulation) 25.853 which governs the requirements for materials used in aircraft interior applications. The aim of this paper is to review a number of newly developed Ciba materials for repair and maintenance with a specific emphasis on technical performance and novel methods of application which can increase cost effectiveness and reduce labour when compared to conventional methods.     

Design and Fabrication of Transparent and Gas‐Tight Optical Windows in Low‐Temperature Co‐Fired Ceramics

Low‐temperature co‐fired ceramics (LTCC) enable the fabrication of microfluidic elements such as channels and embedded cavities in electrical devices. Hence, LTCC facilitate the realization of complex and integrated microfluidic devices. Examples can be applied in many areas like reaction chambers for synthesis of chemical compounds. However, for many applications it is necessary to have an optically transparent interface to the surroundings. The integration of optical windows in LTCC opens up a wide field of new and innovative applications such as the observation of chemiluminescent reactions. These chemical reactions emit electromagnetic radiation and thus offer a method for noninvasive detection. Thin glasses (≤500 μm) were bonded by thermocompression onto a LTCC substrate. As the bonding agent, a glass frit paste was used. Borosilicate glasses, fused silica as well as silicon were successfully bonded onto LTCC. To join materials with a large coefficient of thermal expansion mismatch (i.e., fused silica and LTCC), it is necessary to limit the heat input to the bond interface. Therefore, a heating structure was integrated into the LTCC substrate beneath the bond interface. This bonding process provides a gas‐tight optical port with a high bond strength.     

聚酰亚胺薄膜技术进展与市场前景

聚酰亚胺薄膜是目前世界上性能最好的薄膜类绝缘材料之一,具有优良的力学性能、电性能、化学稳定性以及很高的抗辐射性能及耐高温和耐低温性能,在航空航天、国防军工、新型建材、环保消防等领域中发挥着越来越重要的作用。介绍了聚酰亚胺薄膜的理化性能、制取工艺、技术进展、应用领域及市场前景,并对国内聚酰亚胺薄膜产业的发展提出了一些建议。     

Development of LTCC micro-hotplate with PTC temperature sensor for gas-sensing applications

Low temperature co-fired ceramic (LTCC) micro-hotplates show wide applications in gas sensors and micro-fluidic devices. It is easily structured in three-dimensional structures. This paper presents the low power consumption micro-hotplates which were developed with PTC (positive temperature coefficient) temperature sensor and inter-digitated electrodes. The paper presents two different structures for micro-hotplate with platinum as a heating element. The PTC temperature sensor using two different materials viz. PdAg and platinum paste are developed with micro-hotplates. The simulation has been achieved through COMSOL for LTCC and alumina micro-hotplates. The temperature variation with power consumption has been measured for the developed LTCC micro-hotplates. The change in resistance of PTC temperature sensors was measured with micro-hotplate temperature. The aim of this study was to place a temperature sensor with the gas sensor module to measure and control the temperature of micro-hotplate. A SnO₂ sensing layer is coated on LTCC micro-hotplate using screen printing and characterized for the sensing of carbon monoxide gas (CO). This study will be beneficial for designing hotplates based on LTCC technology with low power consumption and better stability of temperature for gas-sensing applications.     

连续碳化硅纤维增强碳化硅陶瓷基复合材料研究进展

碳化硅纤维增强碳化硅陶瓷基(SiC/SiC)复合材料具有轻质、耐高温、抗氧化的优异特性,在航空领域,如航空发动机的热端构件、高温结构功能一体化构件,航天及空天飞行器热防护结构部件、动力系统热端部件等领域具有广泛的应用前景,受到美国、欧洲、日本等国研究人员的广泛关注。本文从组成、制备工艺、加工工艺和考核应用等方面,综述了SiC/SiC复合材料的国内外研究进展,并指出了目前面临的问题和机遇。     

复合材料用耐高温胶粘剂

讨论了耐高温胶粘剂在国内外的研究和应用情况。复合材料用耐高温胶粘剂的研究开始于20世纪50年代后期,目的是满足航空航天的需要。至今已报道过许多种高温胶粘剂,其中一部分已用于工业生产。这类胶粘剂应用广泛,其中有高速飞机的油箱密封、高速飞机和航天飞机的结构粘接。未来一段时间,市场需求将迅速增加。     

Zero Shrinkage of LTCC by Self-Constrained Sintering

Low shrinkage in x and y direction and low tolerances of shrinkage are an indispensable precondition for high-density component configuration. Therefore, zero shrinkage sintering technologies as pressure-assisted sintering and sacrificial tapes have been introduced in the low-temperature co-fired ceramics (LTCC) production by different manufacturers. Disadvantages of these methods are high costs of sintering equipment and an additional process step to remove the sacrificial tapes. In this article, newly developed self-constrained sintering methods are presented. The new technology, HeraLock^®, delivers LTCC modules with a sintering shrinkage in x and y direction of less than 0.2% and with a shrinkage tolerance of ±0.02% without sacrificial layers and external pressure. Each tape is self-constrained by integration of a layer showing no shrinkage in the sintering temperature range of the LTCC. Large area metallization, integration of channels, cavities and passive electronic components are possible without waviness and camber. Self-constrained laminates are an alternative way to produce zero shrinkage LTCC. They consist of tapes sintering at different temperature intervals. Precondition for a successful production of a self-constrained LTCC laminate is the development of well-adapted material and tapes, respectively. This task is very challenging, because sintering range, high-temperature reactivity and thermal expansion coefficient have to be matched and each tape has to fulfill specific functions in the final component, which requires the tailoring of many properties as permittivity, dielectric loss, mechanical strength, and roughness. A self-constrained laminate is introduced in this article. It consists of inner tapes sintering at especially low-temperature range between 650°C and 720°C and outer tapes with an as-fired surface suitable for thin-film processes.     

Novel Microsystem Applications with New Techniques in Low-Temperature Co-Fired Ceramics

Low-temperature co-fired ceramic (LTCC) enables development and testing of critical elements on microsystem boards as well as nonmicroelectronic meso-scale applications. We describe silicon-based microelectromechanical systems packaging and LTCC meso-scale applications. Microfluidic interposers permit rapid testing of varied silicon designs. The application of LTCC to micro-high-performance liquid chromatography (μ-HPLC) demonstrates performance advantages at very high pressures. At intermediate pressures, a ceramic thermal cell lyser has lysed bacteria spores without damaging the proteins. The stability and sensitivity of LTCC/chemiresistor smart channels are comparable to the performance of silicon-based chemiresistors. A variant of the use of sacrificial volume materials has created channels, suspended thick films, cavities, and techniques for pressure and flow sensing. We report on inductors, diaphragms, cantilevers, antennae, switch structures, and thermal sensors suspended in air. The development of "functional-as-released" moving parts has resulted in wheels, impellers, tethered plates, and related new LTCC mechanical roles for actuation and sensing. High-temperature metal-to-LTCC joining has been developed with metal thin films for the strong, hermetic interfaces necessary for pins, leads, and tubes.     

国产PBO纤维研究现状及发展趋势

综述了国产PBO纤维制备过程中在单体合成、聚合物及纺丝的方面的研究现状,表明PBO的单体合成工艺较为成熟,产品纯度高,满足聚合需求;纤维制备具有较好的技术基础,能小批量提供产品,纤维的力学性能与东洋纺Zylon纤维相当。PBO纤维作为一种高强、高模、耐高温材料在航天航空、国防军工、耐高温及增强材料领域得到了广泛的应用,具有良好的市场前景。     

Environmental damage and degradation of FRP composites: A review report

Fiber‐reinforced plastics (FRP) composites are prime choice materials in various civil engineering structures and high performance aerospace components. They exhibit superior mechanical properties than their metallic counterparts. However, they are susceptible to environmental damages and degradations. To utilize the full potential of FRP composite materials their physical, chemical, and mechanical behavior in different environmental conditions should be well established. Present review is an attempt at highlighting different damage/degradations that may be caused to the FRP composite on its exposure to various environmental conditions. POLYM. COMPOS. 36:410–423, 2015. © 2014 Society of Plastics Engineers     

Fabrication of embedded microfluidic channels in low temperature co-fired ceramic technology using laser machining and progressive lamination

This paper describes the application of laser micromachining techniques for the fabrication of microfluidic channels in low temperature co-fired ceramic, LTCC, technology. It is shown that embedded cavities can be successfully realised by employing a recently proposed progressive lamination process with no additional fugitive material. Various microfluidic structures have been fabricated and X-ray imaging has been used to assess the quality of the embedded channels after firing. The problem of achieving accurate alignment between LTCC layers is addressed such that deeper channels, spanning more than one layer, can be fabricated using a pre-lamination technique. A number of possible applications for the presented microfluidic structures are discussed and an H-filter particle separator in LTCC is demonstrated.     

Integration Concepts for the Fabrication of LTCC Structures

At the Keck Smart Materials Integration Laboratory at Penn State University, low-temperature co-fired ceramic (LTCC) material systems have been used to fabricate a number of devices for a variety of applications. This article presents an overview of the integration of the concepts and materials that we have used to achieve miniaturization and unique device function. Examples of microwave filters, metamaterial antennas, and a dielectrophoretic cell sorter will be presented, with emphasis on device modeling and design, prototype construction methods, and test results.     

水基流延法制备掺杂ZnO-TiO_2系微波介质陶瓷及性能研究

利用低温共烧陶瓷(简称LTCC)技术设计制造片式多层微波器件已成为当今的研究热点。ZnO-TiO2系微波介质陶瓷具有介电常数适中、介电损耗低、频率温度系数可调和低温烧结等特点,它是具有开发价值的LTCC微波介质材料。实验结果表明:在ZnO-TiO2系统中加入微量的添加剂MgCO3与ZrO2,构成双元复合取代掺杂系统Zn1-xMgxTi1-xZrxO3,当x值取0.07时,最佳介电性能为:εr为29.4,Qf为4285GHz,τf为-8ppm/℃,且该微波介质陶瓷适合于水基流延成型和低温烧结,为LTCC微波介质陶瓷产业化打下了良好的基础。     

耐高温胶黏剂

耐高温胶黏剂的研究开始于20世纪50年代后期,目的是满足航空和电子工业的需要。至今已报道过许多种耐高温胶黏剂,其中一部分已用于工业生产。这类胶黏剂应用广泛,其中有刹车系统的粘接、高速飞机的油箱密封、高速飞机和航天飞机的结构粘接。未来一段时间,市场需求将迅速增加。本文讨论了几类可以用来配制耐高温胶黏剂的聚合物,其中有聚苯并噻唑、聚酰亚胺、聚喹噁啉及聚硅氧烷。