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.