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Gas-assisted wafer cooling/heating system is one of the key technologies for manufacturing microelectronic devices. The heat conduction in the gap between wafer and susceptor is modeled here as a one- or two-dimensional (1-D or 2-D) rarefied gas problem. The simulation is performed for monatomic and diatomic gases by means of the Direct Simulation Monte Carlo (DSMC) method. In the 1-D case the gas heat conductivity is obtained for various factors (gas species, surface temperature, energy accommodation coefficient) as a function of the Knudsen number. All numerical data obtained can be summarized by a simple equation: Smoluchowski's equation extended to the free molecular regime. In the 2-D case, the DSMC method is applied to the heat transfer between rough and smooth surfaces. The effect of surface roughness on heat conduction is clarified.

The thermal resistance of a surface-mount, plastic quad flat package was determined over a range of heating powers, air velocities and package orientations. The package was placed in a low-speed wind tunnel which could be rotated in a vertical plane, thereby altering the orientation of the package with respect to the gravity vector. Findings indicated the limits of mixed convection for an horizontal package and of orientation effects for package/tunnel orientations from buoyancy-opposing to buoyancy-assisting.

The impact of chip-mounting attachment on the thermal resistance of GaAs power field effect transistor (FET) modules was studied. The thermal resistance was determined for various GaAs chip thickness by an electrical procedure employing temperature of Schottky-barrier in the GaAs metal semiconductor FETs. The thermal resistance of low-cost epoxy-mounted GaAs chips, applicable for uniplanar monolithic microwave ICs was observed not to increase even up to a chip thickness of 250 microns, while that of AuSn-mounted GaAs chips increased.

A local heat transfer coefficient model is employed for finite element analysis used for determining local temperature and thermal stress response in a convective ceramic ball grid array surface mount package. Comparison of the results with those calculated from the constant heat transfer coefficient model and isothermal model revealed substantial differences. The constant h model results into an underestimation of the temperature at the trailing edge of the package.

Forced convective heat transfer from a micro-finned surface to a fluorocarbon liquid FX3250 was studied. The heat transfer surface is constructed from copper and has 20 longitudinal fins. Results indicated that the sensitivity of heat transfer performance to the change in channel height depends on the kind of heat transfer surface. Findings are in agreement with the heuristic assumption that the increased flow velocity in the free flow area above the fins in higher-height channels result into high heat transfer coefficients on the fin tips, making up for the decrease in heat transfer in the grooves.

An analytical solution for a system composed of a vertical, parallel-plate, isothermal heat sink and a chimney is shown. A ridge of maximum total heat transfer is seen with respect to the plate spacing and heat-sink height. The ridge indicates that heat-sink height may be decreased without degrading the thermal performance for natural air cooling. The flow behavior of optimal systems shows that systems with and without chimneys dissipate maximum heat when the velocity profiles within the heat sink are fully developed and developing, respectively.

A liquid-filled cooling environment can be used to improve the heat dissipation performance of a multichip module (MCM) package. Findings showed that cooling performance improved by two to four times compared to the dry package because of the superior thermal characteristics of dielectric liquids compared to air. Findings also revealed that for any given external boundary condition, the permissible power dissipation did not vary much under various liquid conditions.

Numerical analyses were conducted on manifold microchannel (MMC) heat sinks. MMCs are different from conventional microchannel heat sinks in that the flow length is substantially decreased to a small fraction of the total length of the heat sink. There were areas close to the inlet in which heat transfer was very high. Secondary maxima in heat transfer were observed at the base of the microchannel under the inlet and at the top of the microchannel close to the outlet at very high inlet velocities.

The problem of estimating the geometrical parameters of a heat sink for maximum heat dissipation of power semiconductor devices (PSD) is considered. To this end, an experiment to investigate heat exchange 'in cooling channels under forced movement of dielectric coolant.' The experiment involves 'liquid boiling on finned surfaces' for removing high-intensity heat fluxes from cooled PSD components.

In recent years, straightforward air cooling of semiconductor devices has gradually been replaced by methods using liquid coolants, especially water cooling. In this paper, more advanced cooling devices for hockey-puck-type and module-type semiconductors are suggested. An established heat sink made of aluminum nitride for the water cooling of hockey-puck-type semiconductors has been used as a basis for the development of high-performance heat sinks for increased heat flux densities. By means of thermal and fluid dynamics simulation tools the internal geometry has been optimized with regard to improved heat transfer and reduced pressure drop. The simulation results have been confirmed by a number of experiments using various measuring techniques. As an alternative cooling method for semiconductor modules, a modified baseplate comprising a number of fins for direct water cooling has been suggested. For an intelligent temperature management control algorithms have been developed, resulting in a prototype application-specific integrated circuit which has been implemented for test purposes. Index Terms--Aluminum nitride heat sinks, computational fluid dynamics simulation, controller, heat transfer, semiconductors, thermal management, traction inverters, water cooling.

This paper deals with the thermal management of a TBGA chip carrier package. In TBGA packages the backside of the chip is available for heat sink or heat spreader (cover plate) attach. By attaching a heat sink directly to the chip and using a thin layer of high thermal conductivity adhesive, a very low internal thermal resistance can be achieved. The package is attached to an organic card and placed vertically in a channel. A three-dimensional conjugate heat transfer model is used, accounting for conduction and radiation in the package and card and convection in the surrounding air. A simplified turbulence model is developed to predict temperatures in the low Re turbulence regime. A parametric study is performed to evaluate the effects of card design, air velocities, interconnect thermal conductivities and thermal radiation on the chip junction temperatures. An experimental study was also conducted to verify the model. Even though the geometry is highly complex due to the multilayer construction of the module and the card, agreement between the model and the experimental measurement is excellent. It was shown that radiation heat transfer can be an equally significant mode as convection in the natural convection regime. [S1043-7398(00)01302-5]

An experimental study of forced convection in impinging flow, using fluorocarbon FX3250 and a simulated electronic chip, was performed. A test section consisting of a 35 mm long, 1 mm wide slot nozzle in a 2 mm thick plate offset 2 mm from the heat source was used. The simulated chip array consisted of five foil strip (4 mm wide) heaters, positioned with the center strip directly beneath the slot nozzle. The velocity of the coolant was varied from 0.53 to 5 m/s, and the subcooling in the range from 2 to 21 K. The experiments were conducted focusing on two cases. First, only the center strip was heated. Second, all the heaters were energized, and the strip-by-strip variations of heat transfer were measured. The critical heat flux (CHF) on the center strip, determined by sensing the onset of oscillations and subsequent rapid rise of foil temperatures, was found considerably lower than those predicted by the existing correlations. It is pointed out that the thermal mass of the test heater could be an important factor for the CHF. The heat transfer behavior of other strips showed channel-flow or jet-impingement mode depending on the strip location and the coolant flow rate. [S1043-7398(00)00202-4]

This paper introduces an algorithm that focuses on the placement of the power dissipating chips for multichip module applications. The main design issue is addressed on the chip placement to achieve uniform thermal distribution. Our approach to the placement problem is based on the modified force-directed placement method. The proposed thermal force-directed placement method is to relate the force equations to the power dissipation values of the individual bare chip. Examples of multichip placement are presented. The finite element simulation results are also investigated and compared with quadrisection placement methods. [S1043-7398(00)01002-1]