Aluminum Nitride Heat Sink

Aluminum nitride has outstanding thermal conductivity and is an electrical insulator and heat sink in competition with beryllium oxide and more recently polycrystalline diamond (see Ch. 13). 

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CVD plays an increasingly important part in the design and processing of advanced electronic conductors and insulators as well as related structures, such as diffusion barriers and high thermal-conductivity substrates (heat-sinks). In these areas, materials such as titanium nitride, silicon nitride, silicon oxide, diamond, and aluminum nitride are of particular importance. These compounds are all produced by CVD. 1 1 PI... 

Beryllia (BeO) is an excellent heat-sink material which is presently widely used but is being phased out because it presents acute safety problems.It is being replaced by aluminum nitride which extensively produced by CVD, mostly in Japan (see Ch. 10, Sec. 2).P2]... 

Diamond is an electrical insulator with the highest thermal conductivity at room temperature of any material and compares favorably with beryllia and aluminum nitride. P3]-P5] jg undoubtedly the optimum heat-sink material and should allow clock speeds greater than 100 GHz compared to the current speed of less than 40 GHz. 

Thermally conductive adhesives may be filled with metal, ceramic, or inorganic particles. Silver-filled epoxies have high thermal conductivities, but may not be used where there is a risk of electrical shorting. In such cases, epoxies or other polymers filled with electrically resistive, but thermally conductive materials such as aluminum nitride, boron nitride, alumina, or beryllia must be used. Some applications for thermally conductive adhesives include attachment of power devices, heat sinks, large components such as capacitors and transformers, large ceramic substrates, and edge connectors. 

Aluminum nitride was first produced and identified in 1907 but it is only since the 1980 s that its cost has been sufficiratly reduced to permit the developm t of industrial applications. Japan is the major supplier. Several American companies have recently entered in the competition to supply heat sinks for the electronic industry. 

The aluminum nitride/boron nitride (AIN/BN) composite material is of considerable interest in modem technological applications because of its excellent mechanical, chemical and physical properties. Aluminum nitride and boron nitride are essentially chemically inert materials, stable at elevated temperatures. Furthermore, they are electrically nonconductive, yet possess high thermal conductivity, together widi optical transparency over a wide spectral range, and have excellent dielectric properties. These properties make the AIN/BN composites suitable as an electromagnetic window material, grinding media, heat sink, as well as electric and stmctural materials. 

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