Masako Nakahashi

High thermal conductivity aluminum nitride ceramic substrates and packages

Breakthrough technologies for achieving a whole line of AlN products for wider use in the electronics market are described. These products are: (1) plain substrates; (2) metallized substrates; (3) direct bond copper (DBC) substrates; (4) substrates for thin-film circuits; (5) substrates for thick-film circuits; and (6) cofired multilayer packages. The basic properties of AlN and problems with AlN from the manufacturing process point of view are summarized. The discussion of the breakthrough technologies needed for AlN applications focuses on four problem areas: the realization of the highest thermal conductivity by sintering, pin/lead brazing, the metallization problem for the cofired case and the postfired case, and polishing for a thin-film circuit. AlN applications and market trends are discussed. >

Interfacial reactions between titanium film and single crystal α-Al2O3

Titanium is commonly used to join metals and ceramics by active metal brazing methods. In this work, titanium was sputter deposited on to single-crystal α-Al2O3 substrates and the interfacial reactions between the titanium film and the Al2O3 substrate were studied. Al2O3 was reduced by titanium when samples were annealed at 973 and 1173 K for 300 s in an argon gas flow. Metallic aluminium was produced at the interface, and this diffused from the interface into the titanium film. At 1173 K, the intermetallic compound Ti3Al and the intermediate titanium oxides, such as Ti2O and TiO, were formed. The Al0 diffusion is important in stimulating interfacial reactions.

Solid-state reactions of the Ag-Cu-Ti thin film-Al2O3 substrate system

A new interpretation of the reaction mechanism between active metal thin-film filler and ceramic substrate is proposed. The authors predict the possibility of prebonding reactions, prior to melting of the filler, at the interface of the system described above. To prove this, solid-state reactions of Ag–Cu–Ti thin films on sapphire substrates have been studied with Auger electron spectroscopy (AES) and x-ray diffraction (XRD). Reaction process and products have been clarified at the temperature just below the melting point of the filler. It is evident that Cu 3 Ti 3 O (diamond structure of Fd 3 m ) is formed by the reaction between Cu 3 Ti and O which results from the reduction of sapphire. It seems that Cu 3 Ti 3 O contributes to bonding between metals and sapphire as an intermediate phase.

Phase transformation of yttria-stabilized zirconia plasma-sprayed coatings in a humid atmosphere

The tetragonal to monoclinic phase transformation resulting from the hydrothermal ageing of 4–20 mass % yttria-stabilized zirconia plasma-sprayed coatings formed from commercial powders has been studied with respect to the Y2O3 distribution inside each coating. The phase transformation was prevented when the nominal Y2O3 concentration was greater than 8 mass % with its point to point distribution ranging between 6.82 to 9.90 mass %. It is suggested that a close correlation exists between the durability of the tetragonal phase in a humid atmosphere and the Y2O3 distribution in the tetragonal zirconia coatings. A content of 6.3–6.8 mass % Y2O3 was calculated to be necessary to prevent the transformation.

Joining of ceramics to metals (1): Interfacial reactions between ceramics and metals

(1996). Joining of ceramics to metals (1): Interfacial reactions between ceramics and metals. Welding International: Vol. 10, No. 10, pp. 765-770.

Solid-State Reactions of a 3D-Transition Metal-Ti/Al 2 O 3 System

An interfacial mechanism for reactions between a Me-Ti thin film (Me=3d transition metals; Cu,Ni) and an A1 2 O 3 substrate is newly proposed. It has been clarified that Me 3 Ti 3 O (diamond cubic of Fd3m), which is formed as an intermediate phase in both the Cu-Ti/Al 2 O 3 and Ni-Ti/Al 2 O 3 systems, is responsible for the bonding between Me and A1 2 O 3 . The solid-state reactions of the Me-Ti bilayer film/Al 2 O 3 system were studied with Auger electron spectroscopy (AES) and X-ray diffraction (XRD) to clarify the interfacial reaction between Me-Ti and the A1 2 O 3 substrate. Me 3 Ti 3 O was observed at the interface between A1 2 O 3 and Me after annealing. Me 3 Ti 3 O was formed by oxidation of the Me-Ti compounds. The oxygen which reacted with the Me-Ti compounds has been found to be generated from the reduction of the A1 2 O 3 substrate.

Diffusion-preventive Al2O3 layer growth at the interface of plasma-sprayed niobium and FeCrAlY in a tungsten fibre-reinforced high-temperature superalloy composite

The growth mechanism of a diffusion-preventive layer formed at elevated temperatures (∼1500 K) between the plasma-sprayed niobium layer and the plasma-sprayed FeCrAlY matrix in a tungsten fibre-reinforced high-temperature superalloy composite (Nb-coated W fibre/FeCrAlY composite) was studied. The diffusion-preventive layer was identified as α-Al2O3 by scanning electron microscopy/electron probe microanalysis, energy dispersive X-ray spectrometry analysis, and X-ray diffraction. Heat-treatment experiments were implemented systematically and it was found that the Al2O3 layer was also formed at the plasma-sprayed Nb/rolled FeCrAl interface. No Al2O3 layer, however, was formed either at the rolled Nb/plasma-sprayed FeCrAlY interface or at the rolled Nb/rolled FeCrAl interface. In these cases, an intermetallic compound layer was formed instead. A growth mechanism is proposed in which the Al2O3 is attributed to a chemical reaction between the residual oxygen in the plasma-sprayed niobium and aluminium in FeCrAlY or FeCrAl. The magnitude of the driving force was evaluated by a new model based on thermodyanamics. Numerical calculations have shown that the proposed growth mechanism is thermodynamically reasonable.