The Effect of Processing Parameters on the Physical and Microwave Electrical Properties of Low Temperature Co-fired Ceramics

Abstract

Low Temperature Co-fired Ceramics (LTCC) represent a multilayer electronic packaging technology with the ability to incorporate many electrical components such as conductive, resistive, and dielectric materials, into a single monolithic package. Example devices would include capacitors, inductors, resistors, antennae, transformers, hybrid circuits, etc. In general, the LTCC package consists of a glass/ceramic dielectric and compatible conductive inks (Au, Ag, etc.). The dielectrics and conductors are patterned/laminated to form the desired 3D structure and then co-fired to complete densification. The resulting monolithic block is mechanically robust with a high density of (often buried) electrical components. Typically, LTCC systems have found implementation in circuitry utilizing the RF and microwave frequency ranges. In general, the material design and processing parameters, and knowledge of how these affect the final mechanical and electrical properties of the LTCC package are needed for successful circuit design. The electronic performance of an LTCC dielectric/conductor system (Ferro L8) was investigated as a function of processing parameters (peak fire temperature, temperature ramp rate, furnace air flow, etc.). Comparisons were also made between multiple manufacturing sites as the mentioned processing parameters vary slightly from site to site even with nominally identical set points due to differences in furnace design, fab layout, etc. Material properties of fired parts such as effective permittivity and electrical losses were measured both on bare dielectric using resonant cavity methods and on the dielectric/conductor system as a whole using microstrip transmission line methods to frequencies as high as 50 GHz. Correlations were made between electrical performance and models based on material properties. The effects of varied processing parameters and processing sites were also studied and used to help establish process understanding and improvement with respect to high frequency electrical performance. As an example, optimization of electrical performance could be achieved by adjusting the nominal furnace temperature set point at a specific site where losses were slightly high even with identical processing parameters to those at another manufacturing site.