Transient liquid phase diffusion bonding (TLPDB) is a joining process that has been applied for bonding many

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

lic and

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

systems which cannot be bonded by conventional fusion

welding Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing Fusion welding, fusion. Welding is distinct from lower ...

techniques. The bonding process produces joints with a uniform composition profile, tolerant of surface

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

s and geometrical defects. The bonding technique has been exploited in a wide range of applications, from the production and repair of

turbine engine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directi ...

s in the

aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astrona ...

industry, to

nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced b ...

plants, and in making connections to integrated circuit dies as a part of the

microelectronics Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre-sc ...

industry.

Process

The process differs from

diffusion bonding Diffusion bonding or diffusion welding is a solid-state welding technique used in metalworking, capable of joining similar and dissimilar metals. It operates on the principle of solid-state diffusion, wherein the atoms of two solid, metallic surfac ...

, in which

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

occurs when a

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...

represent element from an interlayer moves into lattice and grain boundaries of the substrates at the bonding temperature. Solid state diffusional processes lead to a change of composition at the bond interface and the dissimilar interlayer melts at a lower temperature than the parent materials. Thus a thin layer of liquid spreads along the interface to form a joint at a lower temperature than the melting point of either of the parent materials. This method differs from brazing in that it is "isothermally solidifying". While holding the temperature above the filler metal melting point, interdiffusion shifts the composition away from eutectic, so solidification occurs at the process temperature. If sufficient interdiffusion occurs, the joint will remain solid and strong well above the original melt process temperature. This is why it is termed "transient liquid phase." The liquid solidifies before cooling.

Interlayer

In this technique it is necessary to select a suitable interlayer by considering its

wettability Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. This happens in presence of a gaseous phase or another liquid phase not miscible with th ...

, flow characteristics, high stability to prevent reactions with the base materials, and the ability to form a composition having a remelt temperature higher than the bonding temperature. The joining technique dates back to ancient times. For example,

copper oxide Copper oxide is a compound from the two elements copper and oxygen. Copper oxide may refer to: * Copper(I) oxide (cuprous oxide, Cu2O) * Copper(II) oxide (cupric oxide, CuO) * Copper peroxide (CuO2) * Copper(III) oxide (Cu2O3) * Copper(IV) oxide ...

painted as an interlayer and covered with

tallow Tallow is a rendering (industrial), rendered form of beef or mutton fat, primarily made up of triglycerides. In industry, tallow is not strictly defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain techn ...

glue Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...

to hold

gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...

balls on to a gold article were heated in a

reducing flame In pyrology, flames are affected by the fuel introduced and the oxygen available. A flame with a good oxygen-fuel ratio is called a neutral flame. The color of the flame is semi-transparent purple or blue. This flame is optimal for all intentions, ...

to form a eutectic alloy alloy at the bond area.

Kinetics

There are many theories on the kinetics of the bonding process but the most common theory divides the process into four main stages. Tuah-poku, I., Dollar, M., Massalski, T.B. " A study of the transient liquid phase bonding process applied to Ag/Cu/Ag sandwich joint". Metallurgical Transactions A. 19(A) (1988), 675-686 The stages are: # dissolution of the interlayer # homogenization of the liquid # isothermal solidification # homogenization of the bond region

References

{{wafer bonding Metallurgy Welding