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Sagging of suspended or laminated structures is a common problem in the processing of Low Temperature Co-Fired Ceramics (LTCC). These glass-ceramic composites are susceptible to plastic deformation upon lamination, or under the stress of body forces once the glass transition temperature of the glass binder is reached during processing. We have designed and fabricated, using the conventional methods of LTCC fabrication, meso-scale structures (ranging in size from 100 mm to 1 cm) to quantify and seek control strategies for this problem. We have implemented bridge structures and membranes to emulate most of the conventional structures encountered during packaging or sensor (actuator) device fabrication.We have observed that when an LTCC tape with holes larger than 400 µm in diameter is laminated, the tapes above and below deform into the cavity. For smaller diameters, deformation is negligible. Bridging structures can be compensated for the potential effect of body forces by screen-printing a thick film over-layer which exert internal tensile stresses on sintering. This can often yield straight bridges. The use of fugitive phase materials, which disappear or flow during firing, is another way of supporting bridging structures. Several of these strategies have been explored, and results are presented.

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Ceramic tape technology was initially developed for efficiently manufacturing interconnects and hybrid microelectronics circuitry through sequential printing and firing of conductor, resistor and/or dielectric paste formulations onto a substrate. Recently, it has been recognized that ceramic tapes can also be used as an efficient and convenient medium for the manufacturing of meso-scale electro-mechanical systems. In the green (pre-fired) state, the ceramic tapes consist of alumina particles, glass frit, and organic binder; and they are soft, pliable, and easily machinable. In each layer, one can machine flow conduits and mechanical devices and print electronic circuits. Very many layers can be stacked together to form complicated, three-dimensional, monolithic structures. These layers can be laminated and sintered. During the sintering process, the organic binder burns out, the glass flows, and the material hardens. It is possible to cast tapes of various ceramic composition to obtain desirable properties. The paper describes mechanical, chemical, and thermal machining of prefired Low Temperature Co-fired Ceramic Tapes (LTCC); the dimensional changes occurring during the lamination and sintering processes; the use of sacrificial layers to prevent the sagging of internal suspended structures during the lamination and firing processes; the bonding of tapes to alumina, silicon, glass, and metals to form a hybrid technology; and the manufacturing of microchannels and a flow sensor in ceramic tapes. Packaging is widely considered to be the Achilles heel of silicon-based MEMS technology since it is difficult to interface silicon MEMS devices with each other and fabricate relatively large, three-dimensional structures. Low Temperature Co-fired Ceramic Tapes (LTCC), the packaging material of choice in the electronics industry, hold the promise of alleviating some of these difficulties.

We have simulated the scattering of UV light in a photo-formable ceramic tape and experimentally measured the transport mean free path (random walk step) between scattering events. After processing the tape we have achieved features size of 70 μm in a 150 μm-thick tape. We were able to predict and control the undercut due to scattering of the light by alumina grains. The experimental verification of the model utilizes a modified version of diffuse-Transmission Spectroscopy (DTS) using the material development characteristics as a sensor. The technique involves the measurement of absorption coefficient by measuring the sample thickness as a function of energy. We also simulated the effect of changing the number density of scatter centers in side-wall morphology.