AlSiC
Encyclopedia
AlSiC, pronounced "alsick", is a metal matrix composite
consisting of aluminium
matrix with silicon carbide
particles. It has high thermal conductivity
(180–200 W/m K), and its thermal expansion
can be adjusted to match other materials, e.g. silicon
and gallium arsenide chips and various ceramic
s. It is chiefly used in microelectronics
as substrate
for power semiconductor device
s and high density multi-chip module
s, where it aids with removal of waste heat
.
Several variants exist:
and Direct Bonded Copper aluminium nitride. It is also compatible with some low temperature co-fired ceramic
s, e.g. Ferro A6M and A6S, Heraeus CT 2000, and Kyocera GL560. Its density at 25 °C is 3.01 g/cm3.
AlSiC composites are suitable replacements for copper
-molybdenum
(CuMo) and copper-tungsten
(CuW) alloys; they have about 1/3 the weight of copper, 1/5 of CuMo, and 1/6 of CuW, making them suitable for weight-sensitive applications; they are also stronger and stiffer than copper. They are stiff, lightweight, and strong. They can be used as heatsinks, substrates for power electronics (e.g. IGBTs and high-power LED
s), heat spreaders, housings for electronics, and lids for chips, e.g. microprocessor
s and ASICs
. Metal and ceramic inserts and channels for a coolant
can be integrated into the parts during manufacture. AlSiC composites can be produced relatively inexpensively (USD 2-4/lb in large series); the dedicated tooling however causes large up-front expenses, making AlSiC more suitable for mature designs. Heat pipe
s can be embedded into AlSiC, raising effective heat conductivity to 500–800 W/m K.
AlSiC parts are typically manufactured by near net shape
approach, by creating a SiC preform by metal injection molding
of an SiC-binder slurry, fired to remove the binder, then infiltrated under pressure with molten aluminium. Parts can be made with sufficiently low tolerances to not require further machining. The material is fully dense, without voids, and is hermetic. High stiffness and low density appears making larger parts with thin wall, and manufacturing large fins for heat dissipation. AlSiC can be plated with nickel
and nickel-gold
, or by other metals by thermal spraying
. Ceramic and metal insets can be inserted into the preform before aluminium infiltration, resulting in a hermetic seal. AlSiC can be also prepared by mechanical alloying
. When lower degree of SiC content is used, parts can be stamped from AlSiC sheets.
The aluminium matrix contains high amount of dislocation
s, responsible for the strength of the material. The dislocations are introduced during cooling by the SiC particles, due to their different thermal expansion coefficient.
A similar material is Dymalloy
, with copper-silver alloy instead of aluminium and diamond
instead of silicon carbide. Other materials are copper reinforced with carbon fiber
, diamond-reinforced aluminium, reinforced carbon-carbon
, and pyrolytic graphite.
Metal matrix composite
A metal matrix composite is composite material with at least two constituent parts, one being a metal. The other material may be a different metal or another material, such as a ceramic or organic compound. When at least three materials are present, it is called a hybrid composite...
consisting of aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
matrix with silicon carbide
Silicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
particles. It has high thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
(180–200 W/m K), and its thermal expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
can be adjusted to match other materials, e.g. silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
and gallium arsenide chips and various ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
s. It is chiefly used in microelectronics
Microelectronics
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture of very small electronic components. Usually, but not always, this means micrometre-scale or smaller,. These devices are made from semiconductors...
as substrate
Substrate (semiconductor)
Substrate is a solid substance onto which a layer of another substance is applied, and to which that second substance adheres. In solid-state electronics, this term refers to a thin slice of material such as silicon, silicon dioxide, aluminum oxide, sapphire, germanium, gallium arsenide , an alloy...
for power semiconductor device
Power semiconductor device
Power semiconductor devices are semiconductor devices used as switches or rectifiers in power electronic circuits . They are also called power devices or when used in integrated circuits, called power ICs....
s and high density multi-chip module
Multi-Chip Module
A multi-chip module is a specialized electronic package where multiple integrated circuits , semiconductor dies or other discrete components are packaged onto a unifying substrate, facilitating their use as a single component...
s, where it aids with removal of waste heat
Waste heat
Waste heat sometimes called Secondary heat or Low-grade heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found. Energy is often produced by a heat engine, running on a source of high-temperature heat...
.
Several variants exist:
- AlSiC-9, containing 37 vol.% of A 356.2 aluminium alloyAluminium alloyAluminium alloys are alloys in which aluminium is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories...
and 63 vol.% silicon carbide. Its thermal conductivity is 190–200 W/m K. Its thermal expansion roughly matches gallium arsenide, siliconSiliconSilicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, indium phosphide, alumina, aluminium nitrideAluminium nitrideAluminium nitride is a nitride of aluminium. Its wurtzite phase is a wide band gap semiconductor material, giving it potential application for deep ultraviolet optoelectronics.-History:...
, silicon nitrideSilicon nitrideSilicon nitride is a chemical compound of silicon and nitrogen. If powdered silicon is heated between 1300° and 1400°C in an atmosphere of nitrogen, trisilicon tetranitride, Si3N4, is formed. The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen...
,
and Direct Bonded Copper aluminium nitride. It is also compatible with some low temperature co-fired ceramic
Low temperature co-fired ceramic
Low temperature co-fired ceramic devices are monolithic, ceramic microelectronic devices. In this context ‘co-fired ceramic’ means that the ceramic support structure and any conductive, resistive, and dielectric materials are fired in a kiln at the same time, and ‘Low temperature’ means that the...
s, e.g. Ferro A6M and A6S, Heraeus CT 2000, and Kyocera GL560. Its density at 25 °C is 3.01 g/cm3.
- AlSiC-10, containing 45 vol.% of A 356.2 aluminium alloy and 55 vol.% silicon carbide. Its thermal conductivity is 190–200 W/m K. Its thermal expansion roughly matches e.g. printed circuit boardPrinted circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
s, FR-4FR-4FR-4 is a grade designation assigned to glass-reinforced epoxy laminate sheets, tubes, rods and printed circuit boards . FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant .FR-4 glass epoxy is a popular and versatile high-pressure...
, and Duroid. Its density at 25°C is 2.96 g/cm3.
- AlSiC-12, containing 63 vol.% of A 356.2 aluminium alloy and 37 vol.% silicon carbide. Its thermal conductivity is 170–180 W/m K. It is compatible with generally the same materials as AlSiC-10. Its density at 25 °C is 2.89 g/cm3.
AlSiC composites are suitable replacements for copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
-molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
(CuMo) and copper-tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
(CuW) alloys; they have about 1/3 the weight of copper, 1/5 of CuMo, and 1/6 of CuW, making them suitable for weight-sensitive applications; they are also stronger and stiffer than copper. They are stiff, lightweight, and strong. They can be used as heatsinks, substrates for power electronics (e.g. IGBTs and high-power LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
s), heat spreaders, housings for electronics, and lids for chips, e.g. microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s and ASICs
Application-specific integrated circuit
An application-specific integrated circuit is an integrated circuit customized for a particular use, rather than intended for general-purpose use. For example, a chip designed solely to run a cell phone is an ASIC...
. Metal and ceramic inserts and channels for a coolant
Coolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...
can be integrated into the parts during manufacture. AlSiC composites can be produced relatively inexpensively (USD 2-4/lb in large series); the dedicated tooling however causes large up-front expenses, making AlSiC more suitable for mature designs. Heat pipe
Heat pipe
A heat pipe or heat pin is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces....
s can be embedded into AlSiC, raising effective heat conductivity to 500–800 W/m K.
AlSiC parts are typically manufactured by near net shape
Near net shape
Near net shape is an industrial manufacturing technique. The name implies that the initial production of the item is very close to the final shape, reducing the need for surface finishing...
approach, by creating a SiC preform by metal injection molding
Metal Injection Molding
Metal injection molding is a metalworking process where finely-powdered metal is mixed with a measured amount of binder material to comprise a 'feedstock' capable of being handled by plastic processing equipment through a process known as injection mold forming. The molding process allows...
of an SiC-binder slurry, fired to remove the binder, then infiltrated under pressure with molten aluminium. Parts can be made with sufficiently low tolerances to not require further machining. The material is fully dense, without voids, and is hermetic. High stiffness and low density appears making larger parts with thin wall, and manufacturing large fins for heat dissipation. AlSiC can be plated with nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
and nickel-gold
Gold plating
Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver , by chemical or electrochemical plating...
, or by other metals by thermal spraying
Thermal spraying
Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means ....
. Ceramic and metal insets can be inserted into the preform before aluminium infiltration, resulting in a hermetic seal. AlSiC can be also prepared by mechanical alloying
Mechanical alloying
Mechanical alloying is a solid-state powder processing technique involving repeated cold welding, fracturing, and re-welding of powder particles in a high-energy ball mill...
. When lower degree of SiC content is used, parts can be stamped from AlSiC sheets.
The aluminium matrix contains high amount of dislocation
Dislocation
In materials science, a dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials...
s, responsible for the strength of the material. The dislocations are introduced during cooling by the SiC particles, due to their different thermal expansion coefficient.
A similar material is Dymalloy
Dymalloy
Dymalloy is a metal matrix composite consisting of 20% copper and 80% silver alloy matrix with type I diamond. It has very high thermal conductivity of 420 W/, and its thermal expansion can be adjusted to match other materials, e.g. silicon and gallium arsenide chips...
, with copper-silver alloy instead of aluminium and diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
instead of silicon carbide. Other materials are copper reinforced with carbon fiber
Carbon fiber
Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...
, diamond-reinforced aluminium, reinforced carbon-carbon
Reinforced carbon-carbon
Carbon fibre-reinforced carbon is a composite material consisting of carbon fibre reinforcement in a matrix of graphite. It was developed for the nose cones of intercontinental ballistic missiles, and is most widely known as the material for the nose cone and wing leading edges of the Space Shuttle...
, and pyrolytic graphite.