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Microwave characteristics of alumina-glass composite multi-layer substrates with co-fired copper conductors
Abstract
This paper presents ceramic multi-layer substrates for mobile communication using alumina-glass composite ceramics and co-fired copper conductors. Electrical characteristics in GHz frequencies of the substrate, copper conductor, transmission line, via hole and coupling between the striplines were evaluated. The results showed that the ceramic multi-layer substrate had good electrical characteristics enough for GHz-band applications. Using the ceramic multi-layer substrates, one can drastically reduce the size of RF circuit boards for mobile communication equipment.
High frequency electrical properties of a high wiring density organic substrate `ALIVH TM', which has any layer inner via holes structure, and Flip Chip interconnection between pads on semiconductor chips and transmission lines using SBB TM technology were characterized. The dielectric constant, the loss tangent, the transmission loss, and the via hole characteristics of the ALIVH substrate were measured from 1 GHz to 4 GHz frequency range. Flip Chip interconnecting region using the SBB technology was also measured using a resonant method and simulated using the FEM method of HFSS. The equivalent circuits of the via hole and the Flip Chip interconnection were evaluated. Both of the ALIVH substrate and the SBB Flip Chip interconnecting technology were found to be good enough to apply to high speed digital systems up to 1 GHz.
The purpose of the present study is to fabricate alumina glass composites by melt infiltration with better dimensional control through reducing both the presintering and infiltration temperature. Main efforts were put to develop glasses that are chemically compatible with alumina. After extensive investigations, a glass of 21SiO2–24B2O3–35Al2O3–15Li2O–5CaO wt.% was successfully developed. The glass shows good chemical compatibility with alumina at elevated temperatures and low viscosity above 900 °C. Dense alumina glass composites can be fabricated by the melt infiltration process at 950 °C, which is 150 °C lower than the current state-of-art. Investigations showed improved net-shape capability for the newly developed composites, where the total linear shrinkage for the sintering and infiltration at 950 °C is less than 0.1%, as compared with the shrinkage of 0.5% induced by the presintering and infiltration at 1100 °C. Preliminary mechanical tests showed that the fracture strength and toughness of the composites are 303 MPa and 3.4 MPa m1/2, respectively. The lower processing temperature and the better dimensional control are the major advantages for the newly developed alumina glass composites.
High-permittivity ceramics make it possible to noticeably miniaturize passive microwave devices. These ceramics must fulfil the requirements of high permittivity, very low dielectric losses and an extremely low temperature dependence of permittivity to yield temperature-stable resonators. Recent progress has been made in understanding the physics of microwave ceramics, particularly the property-structure relationship, in developing new materials with higher permittivity, better temperature stability and considerably lower sintering temperature, and in making co-fired multilayer devices possible, as well as in developing new microwave devices such as oscillators, antennas and band-pass filters.
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