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

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

The present work critically reviews the scientific and patent literature on low melting bismuth based oxide glass frits in materials for electronics, sensors and related applications such as sealing glasses, solar cells, architectural and automotive glass, the main motivation being to replace lead based materials by environmentally more benign ones. Due to similar glass forming properties of Bi and Pb, Bi based glasses are the closest ‘drop-in’ alternative for lead bearing formulations, and are therefore actually replacing them in many applications, helped also by previous experience with Bi containing materials in thick film technology and component metallisations. The outstanding issues are discussed, e.g. matching the lowest processing temperatures achieved by the classical lead based glasses without sacrificing durability and stability, as well as stability versus chemical reduction. Finally, consideration is also given to special ‘heavy’ glasses (often containing Bi and Pb together) that are ...

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Review of Bi2O3 based glasses for electronics and related applications

We describe a scalable method for producing continuous graphene networks by tape casting surfactant-stabilized aqueous suspensions of functionalized graphene sheets. Similar to all other highly connected graphene-containing networks, the degree of overlap between the sheets controls the tapes’ electrical and mechanical properties. However, unlike other graphene-containing networks, the specific surface area of the cast tapes remains high (>400 m2·g–1). Exhibiting apparent densities between 0.15 and 0.51 g·cm–3, with electrical conductivities up to 24 kS·m–1 and tensile strengths over 10 MPa, these tapes exhibit the best combination of properties with respect to density heretofore observed for carbon-based papers, membranes, or films.

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High Surface Area Tapes Produced with Functionalized Graphene

The addition of B2O3 to Ba5Nb4O15–BaNb2O6 significantly lowered the sintering temperature to ∼900 °C in comparison to ∼1250 °C for samples without B2O3. The presence of a B2O3-rich intergranular phase in the sample was observed, which was attributed to the presence of a liquid phase during sintering. The barium metaniobate, BaNb2O6 has two polymorphs, with orthorhombic and hexagonal forms. A major contributor to microwave dielectric properties of low-fired samples is the low temperature phase, hexagonal BaNb2O6. The small amount of hexagonal BaNb2O6 could tune τf of Ba5Nb4O15. Therefore, Ba5Nb4O15–BaNb2O6 with B2O3 can be a suitable for low-temperature cofired ceramic (LTCC), due to its reduced sintering temperature and good microwave dielectric properties: Q×f=28 000 GHz, er and τf are 42 and 0 ppm/°C, respectively. The chemical compatibility of silver electrodes and low-fired samples has also been investigated.

Low-temperature sintering and microwave dielectric properties of Ba5Nb4O15–BaNb2O6 mixtures for LTCC applications

High performance low temperature co-fired ceramic (LTCC) dielectrics is highly desired for next generation information technology. The rational design is a key issue for the development of new LTCC materials. In comparison to the design of conventional electroceramics, more attention should be paid on the formation process of the material structure for that of LTCC, in addition to the physical properties, due to the special requirement in fabrication processing. In this paper, sintering mechanism of three types of LTCC materials, i.e., glass-ceramics, glass ceramic composite, and glass bonded ceramics, as well as important factors of their dielectric properties are discussed and summarized, and the design strategies for LTCC dielectrics, based on new matrix materials with much lower sintering temperature or higher quality, are proposed. As an example for rational design, oxyfluoride glass-ceramic based dielectrics, a new class of LTCC materials with low ɛr, is analyzed.

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Towards rational design of low-temperature co-fired ceramic (LTCC) materials

The chemical, structural and mechanical properties of six commercially available low temperature cofire ceramic (LTCC) systems were evaluated using X-ray diffraction, transmission electron microscopy, energy dispersive X-ray Spectroscopy (EDS), 3 and 4 point bend test, wetting angle and tensile testing (on unfired tape). Each of the systems (by manufacturer) was based on a different devitrifying glass-ceramic system, including Wollenstite, Anorthite and Celsian phases, plus expansion modifiers of alumina. For mechanical properties, both the fired strength and performance of the green, unfired tape were evaluated, including the viscoelastic response of unfired tape.

Chemical, structural, and mechanical properties of the LTCC tapes

The mechanical properties of eight solder alloys from the Pb‐Sn‐In‐Ag alloy systems were determined over the temperature range ‐200°C to 100°C, using uniaxial tensile tests, dynamic mechanical analysis (DMA), acoustic pulse methods and dilatometry. In general, the strength and elastic modulus of the alloys studied was inversely dependent on temperature. PbSn, PbIn and SnIn alloys were observed to turn superplastic with elongations over 100 per cent at temperatures of 50°C or above. The Pb‐based and In‐Sn eutectic solders possessed superplasticity at temperatures greater than 50°C. From these results, deformation and fracture processes are reviewed, and the appropriate fracture mechanism is proposed.

Mechanical properties of Pb/Sn Pb/In and Sn‐In solders

With projected power densities above 500 W/cm 2 for devices, new methods for thermal management from the heat generation at the die to heat removal to the ambient must be addressed. By integrating fluid cooling channels, coupled to the power device with high-density thermal vias and a micro heat exchanger within the ceramic substrate, enhanced thermal management was achieved. New materials and processes were developed to fabricate the unique components required to develop the embedded micro heat exchangers within the substrate. Enhanced thermal vias to minimize the thermal impedance through the ceramic, increasing the effective thermal conductivity from 2.63 to near 250 W/m-K. The use of an organic insert with Ag thick films fabricated into the desired complex heat exchanger requirements, allowed complex free standing metal shapes to be developed within the cavities while ensuring uniform green tape density during lamination prior to tape firing. Large cavities, three-dimensional free standing metal columns and metal foils have been utilized to fabricate prototype heat exchanger configurations. Preliminary thermal performance results for an integrated heat exchanger with a staggered pin fin array are presented. Utilizing water as the working fluid, the prototype heat exchanger is demonstrated to provide an effective thermal resistance of 2.7 °C/W and acceptable operation with a with power densities of 30 W/cm 2 .

Embedded heat exchanger in LTCC substrate

The growing number of applications using high temperature superconductors (HTS) has created new requirement for increasing the range of temperatures in which electronic assemblies can operate. Typically, eutectic lead-tin solders lose ductility below -150/spl deg/C. In this paper, new solder formulations were evaluated for cryogenic applications. The mechanical properties of PbIn and Sn-In solders were determined over the temperature range -200/spl deg/C to 100/spl deg/C using the uniaxial tensile test, with the following results. The strength of two types of solder increases almost linearly with decreasing temperature. However, it was evident that the Sn-In alloying solders possess higher strength than the Pb-In (50 Pb/50 In) solder at low temperatures. For both types of solder, the total elongation decreases with decreasing temperature, and all of the solders displayed superplasticity at temperatures greater than 50/spl deg/C. There was also doubling of the uniform elongation below -50/spl deg/C for all of the tested solders. The deformation and fracture processes of the solders were investigated, and their fracture mechanism is proposed.

Yanqing Liu

Papers

Chemical, structural, and mechanical properties of the LTCC tapes

Mechanical properties of Pb/Sn Pb/In and Sn‐In solders

Embedded heat exchanger in LTCC substrate

Mechanical properties of Sn-In and Pb-In solders at low temperature

LTCC substrates with internal cooling channel and heat exchanger