Low-temperature Co-fired Ceramic Green Tape Research Articles

Application of composite binders in the fabrication of LTCC green tape based on the borosilicate glass/Al2O3 system with optimized Ca/Mg ratios

This study aimed at developing a high-performance low temperature co-fired ceramic (LTCC) green tape with good sintering characteristics and dielectric properties based on a borosilicate glass/Al2O3 system. First, the Ca/Mg ratio in the glass composition was optimized to modify the microstructure, sintering density, and dielectric properties. Subsequently, composite binders of various molecular weights were employed in the tape casting slurries, to improve the performance of the green tapes. Following a comprehensive analysis of the multiple necessary performance parameters, we concluded that the glass/Al2O3 composite with Ca/Mg = 4.30 sintered at 875 °C presented a dense microstructure with outstanding sintering characteristics and dielectric properties (density of 3.14 g/cm3, permittivity of 8.02 and dielectric loss of 11 × 10−4 (10 MHz)). The application of composite binders with 60% B20H and 40% B79 yielded a green tape with a high density (1.94 g/cm3), smooth surface (Ra = 213 nm), and good workability. In addition, the thermal and mechanical properties of the optimized composite were practical for electronic packaging applications. This positive assessment of the co-firing compatibility between the composite and Ag electrodes augments its application potential for LTCC technology.

Influence of CaO–B2O3–SiO2 crystallizable glass on microstructure and microwave dielectric of LiMg0.9Zn0.1PO4 ceramics for LTCC substrate applications

The low temperature co-fired ceramic (LTCC) material was developed with the LiMg0.9Zn0.1PO4 ceramic added CaO–B2O3–SiO2 crystallizable glass via the traditional solid-state reaction process. The addition of CBS glass can reduce the sintering temperature of LiMg0.9Zn0.1PO4 ceramic from 950 °C to 850 °C without an obvious degradation of the microwave dielectric properties as the low-loss phases CaSiO3 and CaB2O4 phases were crystallized during sintering. The LiMg0.9Zn0.1PO4-15 wt% CBS2 glass composite sintered at 850 °C for 15 min exhibited the εrvalue was 6.7, the Q × f value was 40,100 GHz at 15 GHz, and the τf value was −44 ppm/°C. The LTCC green tape based on the optimized LiMg0.9Zn0.1PO4-CBS2 glass composite composition was obtained by the standard tape-casting process. Tapes with Ag conductor paste printed were laminated and co-fired at 850 °C which revealed the good compatibility between the ceramic and silver. The sintered ceramic demonstrated the CTE value of 8.5 ppm/°C (25 °C–300 °C), the maximum thermal conductivity of 5.6 W/M·K at 25 °C and the flexural strength of 180 MPa, indicating it was a promising LTCC substrate material.

Fabrication of Microstructures in LTCC Technology Using Selective Laser Ablation

This paper presents a technique and initial conditions for the laser ablation of microstructures in a low temperature co-fired ceramic (LTCC) technology. It is demonstrated that 2.5-D microstructures can be realized cost effectively and precisely by deploying the proposed technique in which an infrared laser is used to carefully ablate portions of unfired LTCC green tape. A demonstration prototype consisting of three gears and their mounting platform is realized along with a detailed description of the attendant micromachining process. The ablated surface is examined using a scanning electron microscope and a surface profiler. The optimization of the laser parameters required to equalize the surface roughness of the ablated material to that of an unmachined LTCC substrate is also described.

Design of an LTCC Structure for a Micro-Ceramic Combustor

Advanced micro- or macro-systems are in some cases made with multilayer ceramic technology. Low-Temperature Co-fired Ceramic (LTCC) technology is considered as one of the more suitable technologies for the fabrication of ceramic micro-systems that integrate screen-printed, thick-film electronic components as well as three-dimensional buried structures, for example, cavities and channels. One of the applications is a ceramic combustor. The chemical energy of the fuel is converted into thermal energy in a chemical micro-combustor through a burning process, while the accompanying high temperatures and, frequently, high pressures impose harsh conditions on the combustor structure. Therefore, the combustor must be carefully designed not only from the functional, thermal and chemical points of view, but also with respect to the mechanical strength. The combustor device was prepared by laminating of Du Pont 951PX LTCC green tapes. The fabricated 3D LTCC structures with buried cavities and channels including two inlets (for fuel and air), the evaporator for the fuel, the mixing system of the channels (for mixing the evaporated fuel and air), the distribution channels and eight microburners were realized. The main parts are eight micro-burners realized as buried cavities. In the burners a platinum-based catalyst was deposited to assist the oxidation, i.e., the burning, of the methanol with the air. Thickfilm, platinum-based heaters and temperature sensors are incorporated within the structure. The device was tested with different flow rates of liquid methanol (1 ml/h to 5 ml/h) and air (7 l/h to 15 l/h). The obtained temperatures were between 250°C and 450°C.

Design and Fabrication of an LTCC Structure for a Microceramic Combustor

Advanced microsystems or macrosystems are in some cases made with multilayer ceramic technology. Low-temperature cofired ceramic (LTCC) technology is considered to be one of the more suitable technologies for the fabrication of ceramic microsystems that integrate screen-printed, thick-film electronic components as well as three-dimensional buried structures, for example, cavities and channels. One of the applications is a ceramic combustor. The chemical energy of the fuel is converted into thermal energy in a chemical microcombustor through a burning process, while the accompanying high temperatures and, frequently, high pressures, impose harsh conditions on the combustor structure. Therefore, the combustor must be carefully designed not only from the functional, thermal, and chemical points of view, but also with respect to the mechanical strength. The combustor device was prepared by lamination of Du Pont 951PX LTCC green tapes. The fabricated 3D LTCC structures with buried cavities and channels including two inlets (for fuel and air), the evaporator for the fuel, the mixing system of the channels (for mixing the evaporated fuel and air), the distribution channels and eight microburners were realized. The main parts are eight microburners realized as buried cavities. In the burners, a platinum-based catalyst was deposited to assist the oxidation, that is, the burning, of the methanol with the air. Thick-film, platinum-based heaters and temperature sensors are incorporated within the structure. The device was tested with different flow rates of liquid methanol (1 mL/h to 5 mL/h) and air (7 L/h to 15 L/h). The temperatures obtained were between 250°C and 450°C.

Cold Chemical Lamination—New Bonding Technique of LTCC Green Tapes

The low‐temperature co‐fired ceramic (LTCC) technology enables fabrication of sensors, actuators, microfludic devices2 and fuel cells. The structures consist of screen‐printed components, gas/liquid channels, reactive chambers and mixers. The lamination process determines the quality of such devices. Thermo‐compression is the most popular bonding method. The LTCC green tapes are joined together at high temperature (up to 80°C) and high pressure (up to 30 MPa) for 2 to 15 minutes. The method allows good encapsulation of the LTCC structures, but the channels geometry is strongly affected by elevated temperature and pressure. Cold Chemical Lamination (CCL) is a new LTCC green tapes bonding technique, which allows for fabrication of 3D modules. A solvent‐based method is used in the CCL lamination instead of the thermo‐compression process. A special liquid agent is screen‐printed on the green tape in the CCL method. The liquid melts the tape surface. Then the tapes are stacked and compressed at room temperature by a printing roll. The influence of the CCL and the thermo‐compression methods on the chamber's geometry quality as well as basic electrical properties of screen‐printed resistors (sheet resistance Rφ standard deviation of sheet resistance σR, variability coefficient of sheet resistance VR, and long‐term stability) are analyzed and compared in this paper. The bonding quality is examined by a scanning electron microscope (SEM).

Particle Shape and Size Effects on Anisotropic Shrinkage in Tape‐Cast Ceramic Layers

The particle shape of a commercial low‐temperature cofired ceramic (LTCC) composite powder was determined quantitatively in the as‐received and milled state using a new particle image analyzer. All grades of the milled powder with average particle sizes of 3.0, 2.4, and 1.8 μm, respectively, exhibit a considerable stretched particle shape, because 40% of their particles have circularity values below 0.95. On the basis of the fast particle image analyzer, the influence of the raw materials on particle alignment during tape casting was investigated using “design of experiments” (DOE). In the cast LTCC green tapes, the degree of particle orientation was measured and correlated with the information from the particle shape analyses and with other material and process factors from the DOE. The results showed that the degree of particle alignment correlates significantly with the measured particle shape and size; more than 80% of the particles were oriented in the casting direction if their shape factor was below 0.5. The particle orientation causes shrinkage anisotropy. The use of a coarser LTCC powder with an average particle size d50 of 3.0 μm instead of 1.8 μm increased the sintering anisotropy factor of LTCC tapes and laminates significantly from 1.0% to 1.85% and from 3.6% to 7.6%, respectively. The use of more binder or less solvent led to higher shrinkage anisotropies too. The casting velocity showed only a minor effect on the degree of particle orientation and sintering anisotropy, which is due to the shorter shearing period in which particle rotation can take place.