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|Surface Characteristics of LTCC Substrates fabricated by pressure-assisted sintering|
|Keywords: LTCC, pressure-assisted sintering, surface quality|
|Low temperature co-fired ceramics (LTCC) are frequently used substrate materials in microsystems technology. The possibility to integrate conducting lines and passive devices into a multilayer substrate facilitates miniaturization and reduces efforts for subsequent packaging. However, due to shrinkage and distortion conventionally co-fired substrates do not fulfill increased requirements regarding planarity and dimensions precision without subsequent machining. Improved substrates with excellent planarity and zero lateral shrinkage can be produced by pressure-assisted constrained sintering. This approach is appropriate for single modules as well as for panel production. In preparation of the sintering process the green multilayer has to be sandwiched between release tapes, typically alumina green tapes, in order to separate the LTCC from the pressing tool. Thereby surface properties of the sintered substrate, such as structure, roughness or thin film capability, are significantly affected. The objective of the study presented is to evaluate which surface qualities can be achieved by pressure-assisted sintering of a commercial LTCC green tape (DuPont™ GreenTape™ 951). Sinter-pressed substrates, fired with release tapes with different particle sizes either laminated or simply placed on the surface, are characterized by surface roughness and thin film capability. The latter is evaluated be the measurement of sheet resistance of different metal thin films on the surfaces. Planarity of sinter-pressed and conventionally sintered substrates is evaluated and compared by scanning optical profilometry. Furthermore, the use of vitreous carbon as pressing plate is tested to substitute the alumina release tape for the production of LTCC substrates with average surface roughness below 50 nm, zero lateral shrinkage and high planarity.|
BAM Federal Institute for Materials Research and Testing