Heat sink materials

Electronic. Diamonds have been used as thermistors and radiation detectors, but inhomogeneities within the crystals have seriously limited these appHcations where diamond is an active device. This situation is rapidly changing with the availabiHty of mote perfect stones of controUed chemistry from modem synthesis methods. The defect stmcture also affects thermal conductivity, but cost and size are more serious limitations on the use of diamond as a heat sink material for electronic devices. 

To remove this unwanted heat (also known as thermal management), it is often necessary to use hybrid circuits and bulky heat-dissipation devices or complicated and expensive refrigeration. Metals with good thermal conductivity, such as copper or aluminum, are presently used as heat sink materials but, since being metals they also have high electrical conductivity, they require an electrical-insulation barrier. 

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. 

G.A. Lane, J.S. Best, E.C. Clarke et al., Solar Energy Subsystems Employing Isothermal Heat Sink Materials, ERDA Contract No. NSF-C906. The Dow Chemical Company, Midland, MI, 1976. 

The mass of heat sink material required to satisfactorily condense the rocket gas flow for a specified run time is a function of several rocket parameters and heat sink material properties. To a suitable approximation, the specific impulse of the rocket fuel determines the amount of energy per unit fuel mass that must be removed by the heat sink, and the fuel mass flow is determined by the ratio of rocket thrust to specific impulse. The heat capacity of the heat sink material along with the allowable material temperature rise during the rocket firing imply the required heat sink mass ... 

Beryllium is also used as a missile part and in other weapons. Owing to both its high thermal conductivity and high electrical resistivity, it is also used as a heat-sink material in electronic devices requiring good electrical insulation properties. In conclusion, some 60% of beryllium consumption is as a constituent of alloys and oxides in electronic parts and some 20% in the same form for electrical components. Approximately 13% is consumed as an alloy, oxide, or metal in aerospace and defense applications, while the balance is used as an alloy, metal, or oxide for other purposes. 

RCO combines both energy saving approaches to achieve the best overall energy efficiency for an oxidation abatement system. RCO systems can provide the high heat recovery efficiency of an RTO system and with special catalyst-coated media installed on top of the heat sink material RCO systems can also provide VOC destruction at lower temperatures than those associated with catalytic oxidation to further reduce energy requirements. 

Figure 7.19 shows a schematic diagram of an RCO system. The basic operation of an RCO system is essentially the same as an RTO unit, with the only difference being lower oxidation temperatures. Thus, essentially all RTO units can be converted to RCO simply by placing a catalyst layer on top of the heat sink material. Also, since oxidation reactions occur at the catalyst rather than in the oxidation chamber, the volume of the oxidation chamber in an RCO unit can be significantly smaller than that in an RTO unit. " ... 

Design considerations for these applications must include thermally conductive parts (heat sinks) for removing heat from the circuitry involved. The circuitry may or may not be encapsulated. In confined circuitry, as on a printed-circuit board, nonencapsulated heat sinks bonded in place are one solution. In this case, aluminum is usually the preferred heat-sink material because of its lightweight and high thermal conductivity. If good dielectric properties are required, a high concentration of inorganic or mineral fillers can be used. 

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