Investigation of sacrificial layers for 3D LTCC structures and some preliminary results

Modern advanced 3D microelectronic packages are in many cases made as multilayer ceramic modules with integrated electronic components and sub-circuits. The Low Temperature Co-Fired Ceramics (LTCC) technology is considered as one of more advanced technologies for fabrication of these structures. The increasing versatility of LTCC technology applications is a consequence of such attractive features of this technology as possibility of creation of three-dimensional structures as many of applications demand possibility of structuring of channels, cavities and reaction chambers, membranes and free-standing beams within LTCC ceramics. To obtain these buried structures without delamination and/or sagging during lamination processes (compressing of green LTCC foils at around 70°C) so called sacrificial layers are often used. During lamination sacrificial layers (screen printed thick film pastes or tapes) support buried cavities. During firing layers must burn out before LTCC tapes are densely sintered to enable the diffusion of air into structures. Six different carbon based materials (four pastes and two tapes) were evaluated. The thermo gravimetrical analysis (TGA) was used to determine the optimised burn-out temperatures and times. LTCC test structures were designed to evaluate the “quality” of buried cavities with different sacrificial materials and with different processing parameters.