Showing papers on "Electronics cooling published in 1994"

Gas-assisted evaporative cooling of high density electronic modules

Abstract: Reliable operation of advanced microelectronic components in three-dimensional packaging configurations necessitates the development of cooling systems capable of removing high heat fluxes and very high heat densities. A recently patented thermal management technique, using high velocity flow of a liquid-gas mixture in the narrow channels between populated substrates, appears to provide such a thermal transport capability. A prototype, high packaging density module, relying on this approach, has been successfully operated and a research study, focusing on the heat transfer rates attainable with this technique in a single, asymmetrically-heated channel has been completed. This paper begins with a description of this gas-assisted evaporative cooling approach, its advantages in thermal packaging of microelectronics, and its implementation in a prototype high-performance computer module. Attention is then paid to theoretical considerations in the flow of gas-liquid-vapor mixtures in narrow parallel plate channels and to the design and operation of an appropriate experimental apparatus. Next, experimental results for the wall temperature, heat transfer coefficients, and pressure drops are presented and compared to theoretical predictions. The paper concludes with a discussion of the thermal packaging potential of this novel thermal management technique. >

Advanced micro air-cooling systems for high density packaging

Abstract: Future 3D electronics packaging systems will require micro cooling systems that can be integrated and permit the continued use of air as a coolant. To achieve this, new types of silicon micro heat exchangers were made using an anisotropic etching process. Various heat exchanger configurations and sizes were made using sandwich and stacking techniques. They can be used either as a heat exchanger for direct cooling with compressed air or as a heat pipe and thermosyphon for indirect cooling with fan-blown air. The performance characteristics of the various cooling systems are stated. The micro-heat-pipe can be used for power loss densities of up to 3 W/cm/sup 2/, the direct air cooling up to 15 W/cm/sup 2/ and the thermosyphon up to 25 W/cm/sup 2/. Cooling performances are achieved that are otherwise only possible with liquid cooling. The practical application of the micro cooling system is demonstrated using the example of the Pentium processor. With a power loss of 15 W, the micro cooling system is able to limit the increase in operating temperature to 15 K. The volume of the micro heat exchanger is 2.5 cm/sup 3/ and therefore considerably smaller than that of standard heat sinks. >

Microelectronics cooling and SEMI-THERM: a look back

Abstract: For the occasion of the 10th anniversary of the SEMI-THERM conference, this paper provides a look back at some of the developments that have taken place since its founding. Topics covered include thermal measurement, thermal characterization, thermal analysis and modeling, air cooling, water cooling, and immersion cooling. >

A boundary element formulation of the conjugate heat transfer from a convectively cooled discrete heat source mounted on a conductive substrate

Abstract: A novel formulation is presented for solving the conjugate heat transfer problem that arises due to a thin flush heat source mounted on a conductive substrate. The geometry is a paradigm for direct air cooling of components on conducting boards. PCB thermal algorithms based on this approach are being developed for rapid estimation of the thermal field in a direct air cooled board. The algorithms are part of a suite of tools for integrated electronic packaging design being developed at the Center for Electronic Packaging Research (CEPR). This paper presents the formulation of the approach and demonstrates its utilization for parametric studies of board level thermal management, in particular for studying the effects of board conductivity. The unique formulation allows one to couple a wide variety of flow models to the solid conduction. The solid side is modelled with a Boundary Element Method (BEM). The temperature field in the fluid side is not explicitly solved, rather, analytical "step temperature" solutions, relevant to the particular flow model, are used to express convective heat flux as a function of interface temperatures. A non-iterative solution for the conjugate problem is found by matching the temperatures and fluxes at the solid-fluid interface. Results of a parametric study of the effects of board conduction on component thermal performance are presented. >

The Effects of Channel Curvature and Protrusion Height on Nucleate Boiling and the Critical Heat Flux of a Simulated Electronic Chip

Abstract: : The quest for higher power yet smaller electronics has given rise to the need for very effective cooling of these electronics. Because one of the foremost problems in electronics cooling is achieving high heat flux cooling within small packages while expending minimal pumping power, one focus of this study was to investigate the effects of channel curvature on the CHF. Experimental data were obtained for flow rates of 1-7 m/s, subcoolings of 5-35 deg C, and radii of curvature of 25.4 and 50.8 mm. A correlation was obtained for these data which provided an excellent fit. One condition that has been ignored in the literature is the effect of the simulated heat source not being flush with the flow channel wall. In manufacturing an electronics cooling device, it will be very difficult to maintain the flush chip condition because of the dissimilar materials involved and the numerous thermal cyclings that the device will go through. Experiments showed a significant effect on CHF of the simulated heat source not being flush. A series of data was obtained for flow velocities of 1-4 m/s and subcoolings of 20-35 deg C. CHF data were obtained for a surface recessed 0.127 mm, a flush surface, and surfaces protruded 0.229, 0. 457, and 0.635 mm into the flow stream.

A parametric study of heat spreading through multiple layer substrates

Abstract: A double Fourier series technique is used to develop an analytical expression for the three-dimensional temperature field within a thin multiple layer substrate cooled by convection and heated by sources mounted on one side. The temperature distribution, in a dimensionless form, is a function of nondimensional parameters: the Biot number, aspect ratios and conductivity ratios of each layer, and the ratios of Fourier coefficients which describe the sources. A parametric study is presented to illustrate the influences of these parameters for a practical electronics cooling problem. Equivalent series and parallel orthotropic conductivity components are derived which can be used to model multiple layer structures as single layers.