The challenge of ceramic/metal microcomposites and nanocomposites

The objective of this review is to study the effect of minor alloying and impurity elements, typically present in electronics manufacturing environment, on the interfacial reactions between Sn and Cu, which is the base system for Pb-free soldering. Especially, the reasons leading to the observed interfacial reaction layers and their microstructural evolution are analysed. The following conclusions have been reached. Alloying and impurity elements can have three major effects on the reactions between the Sn-based solder and the conductor metal: Firstly, they can increase or decrease the reaction/growth rate. Secondly, additives can change the physical properties of the phases formed (in the case of Cu and Sn, ɛ and η). Thirdly they can form additional reaction layers at the interface or they can displace the binary phases that would normally appear and form other reaction products instead. Further, the alloying and impurity elements can be divided roughly into two major categories: (i) elements (Ni, Au, Sb, In, Co, Pt, Pd, and Zn) that show marked solubility in the intermetallic compound (IMC) layer (generally take part in the interfacial reaction in question) and (ii) elements (Bi, Ag, Fe, Al, P, rare-earth elements, Ti and S) that are not extensively soluble in IMC layer (only change the activities of species taking part in the interfacial reaction and do not usually participate themselves). The elements belonging to category (i) usually have the most pronounced effect on IMC formation. It is also shown that by adding appropriate amounts of certain alloying elements to Sn-based solder, it is possible to tailor the properties of the interfacial compounds to exhibit, for example, better drop test reliability. Further, it is demonstrated that if excess amount of the same alloying elements are used, drastic decrease in reliability can occur. The analysis for this behaviour is based on the so-called thermodynamic–kinetic method.

Impurity and alloying effects on interfacial reaction layers in Pb-free soldering

The variations with time of the contact angle formed by molten pure aluminium or Al-Si alloys with single crystalline SiC were measured by the sessile drop method in a vacuum of 10−4 to 10−5 Pa at temperatures ranging from 933 to 1200 K. In the Al/SiC system, a “non-wetting-wetting” transition was observed at a temperature that decreases as time increases. After holding times of about 2 h, contact angles were stabilized to acute angles even at the aluminium melting point. Although additions of silicon to aluminium were in such amounts as to prevent Al4C3 formation at the interface, wettability in both pure Al/SiC and Al-Si alloys/SiC systems was not observed to differ appreciably.

Wettability of SiC by aluminium and Al-Si alloys

Chemical bonding, chemical reaction, and the interfacial structure of metal/ceramic interfaces are reviewed with particular emphasis placed on Al and Ti alloys bonded to Al2O3 and SiC ceramics. It is shown that a number of important properties of metal/ceramic interfaces such as the wetting behaviour and work of adhesion can be predicted qualitatively from simple bonding models based on the elements in the metal and ceramic. A variety of chemical reactions can occur at metal/ceramic interfaces and equilibrium thermodynamics is useful in predicting possible reactions. The kinetics of reaction at metal/ceramic interfaces generally follow a parabolic rate law and reaction layers thicker than about 1 μm usually have a deleterious effect on interface strength. Interfacial energy minimisation dominates the atomic structure of metal/ceramic interfaces with the result that close packed planes and directions in the metal, ceramic, and reaction product when present, are often parallel across the interface. ...

Bonding, structure, and properties of metal/ceramic interfaces: Part 1 Chemical bonding, chemical reaction, and interfacial structure

Silicon carbide fibres and their potential for use in composite materials. Part 1

The wettability of alumina by ternary alloys of copper, titanium and aluminium, gallium gold, indium, nickel or silver has been investigated using sessile drop tests conducted in vacuum at 1050–1250° C. Substantial additions of titanium are known to induce copper to wet alumina due to the formation of a titanium rich reaction product at the alloy/ ceramic interface, but the present work has shown that the concentration of titanium can be reduced by the addition of ternary alloying elements. Additions of indium are very beneficial, of aluminium, gold or silver are moderately beneficial, and of gallium or nickel are of negligible benefit or detrimental. These observations, and previous work with copper-tin-titanium alloys [1] can be interpreted in terms of effects on the activity of titanium which it is argued will be enhanced if the ternary alloying element has a low surface energy and is readily saturated by titanium. The correlation of the experimental wetting observations with the surface energy and titanium solubility data for the ternary alloying elements provides a basis for the rational development of reactive metal brazes for joining unmetallized ceramics.

The wetting of alumina by copper alloyed with titanium and other elements

With $a$ major increase in the integration of renew-able energy sources, along with the use of solar inverters, the need for smart inverter technology is higher than ever. It is desirable for these smart inverters to have high power density, operate with maximum efficiency, and provide grid services such as voltage and frequency regulation. The power delivery of these grid-supporting inverters can be regulated through output current control, which is varied based on sensed grid conditions. This paper details the analysis, design, and hardware testing of a 3-ϕ smart inverter that monitors grid conditions and dynamically alters the active and reactive power fed to the grid as needed, thus providing grid services through voltage and frequency regulation. Controller design calculations are presented, and simulation results of transient conditions are provided. Experiments on a 1 kVA hardware prototype using a grid emulator show proof-of-concept for a highly efficient 3-ϕ smart solar microgrid inverter.

M. J. Waite

Papers

The wetting of alumina by copper alloyed with titanium and other elements

Design and Control of Three-phase Smart Inverter Using Gate-drive Integrated Gallium Nitride (GaN) Devices for Solar Energy Integration