Meso (Intermediate)-Scale Electromechanical Systems for the Measurement and Control of Sagging in LtcC Structures

Abstract

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.

Carbon burnout and densification of self-constrained LTCC for fabrication of embedded structures in a multi-layer platform

“…One of the fabrication challenges is that the embedded structures tend to deform and sag during lamination and/or co-firing. [1][2][3][4] This sagging of the embedded structures is due to the non-elastic deformation of the suspended LTCC laminates over the structures subjected to a high lamination pressure (10.3-20.7 MPa) during lamination. During co-firing, LTCC materials undergo debinding and sintering.…”

“…2 However, it was necessary to chemically etched away the glass after sintering and complete removal was difficult. Screenprinted thick film that shrinkage-matched with LTCC was also used as supporting structures to compensate for the deformation induced by the body force during sintering.…”

“…Screenprinted thick film that shrinkage-matched with LTCC was also used as supporting structures to compensate for the deformation induced by the body force during sintering. 2 To support the embedded structures during lamination and sintering, an insert that could be removed after sintering was used. 10 However, a major limitation is that lamination with the insert is not feasible in fabricating enclosed structures.…”

“…These fugitive materials include waxes, 11 polymeric materials, 7,11,12 and carbon materials. 1,2,4,13 Waxes and polymeric materials were completely burnt out before the sintering of LTCC laminate, thus no support was provided to the structure during sintering. Controlling of carbon burnout inside the embedded structures provides the opportunity to maintain the carbon as supporting material for the structure during sintering.…”

“…Since carbon burnout could be suppressed under an inert atmosphere, switching between inert and oxidizing atmospheres was used to control the carbon burnout. 1,2 Another alternative way to control the carbon burnout was by tailoring carbon materials with different carbon particle sizes to ensure complete burnout before pore elimination in LTCC. 4 For the potential of supporting the embedded structures during both lamination and sintering, lamination with carbon material is one of the popular approaches in realizing structures in a LTCC platform.…”