tailieunhanh - Heat Transfer Handbook part 100

Heat Transfer Handbook part 100. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | 986 HEAT TRANSFER IN ELECTRONIC EQUIPMENT the lateral conductivity and the transverse through the thickness conductivity is sufficient to achieve the desired accuracy. As in all discretized thermal models the error inherent in this technique is inversely proportional to the volume represented by each resistor. Because the copper and dielectric layers in the board may not be continuous due to the presence of traces and vias it is very difficult to model the conduction in this layer in full detail. If nc is the number of cutouts holes for interconnection and etched copper in the copper layers and dc is the diameter of each cutout a conduction factor forconduction normal to the copperlayers may be defined as Kn WL - . WL where W and L are the width and length of the printed circuit board respectively. The factor Kn simply represents the fraction of the conduction area missing due to the cutouts. Similarly a conduction factof for toe in-a nand dueotton may be finked as k W -ncdc W The thermal resistance of each of the layers making up the printed circuit board in the normal direction can be written as v Rn KpkXLW 13 56 where 8x and kx are the thickness and thermal conductivity of layer x. Similarly the thermal resistance of each of the layers in the iniplane direction can be written as RP ------L------ x Kpkx U 7 The thermal resistances of the various layers are in series in the normal direction and in parallel in the in-plane direction. Using the law of electrical resistances the total resistance R. in the normal direction can be written as R. V kenLW kxLW where e is the total thickness of the interposer or motherboard and ken is the equivalent normal thermal conductivity. Similarly the total resistance Rp in the in-plane direction can be written as -1 k-PW W Rp L L 7 LENGTH-SCALE EFFECTS ON THERMOPHYSICAL PROPERTIES 987 Equations and can be used to estimate the equivalent in-plane and normal thermal conductivities for the .

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