Local jet impingement boiling heat transfer

Multichip modules provide shorter interconnection lengths between the chips, higher speeds and lower costs. This higher system performance is the driving force for advances in MCM packaging technology. A potential limitation is the ability to remove heat from these packages. With higher chip densities, the thermal management of multichip modules poses a real challenge to the package manufacturer. There is a need to define the junction-to-ambient and junction-to-case thermal resistances for multichip modules in a more rigorous manner while reducing the number of thermal tests needed to evaluate an MCM and provide information to predict junction temperatures under arbitrary powering up of the individual dice. For high reliability, it is critical that maximum specified operating junction temperatures are not exceeded. Experiments were performed for nonuniform powering up of an MCM mounted on a vertical board in natural and forced convection. The package tested was a 208-lead Amkor PMCM. The average chip temperature due to multiple sources within the module was considered as the reference temperature for evaluating the junction temperature rise of the particular chip. The concept of superposition of temperatures was found to capture the effect of the background heating of the chip due to its neighbors as well as the individual power dissipation from the chip in question. This approach offers a more refined methodology for evaluation of nonuniformly powered multichip modules compared to previous methods.

Methodology for thermal evaluation of multichip modules

Experiments have been performed using water and FC-77 to investigate heat transfer from an in-line 1 x 10 array of discrete heat sources, flush mounted to protruding substrates located on the bottom wall of a horizontal flow channel. The data encompass flow regimes ranging from mixed convection to laminar and turbulent forced convection. Buoyancy-induced secondary flows enhanced heat transfer at downstream heater locations and provided heat transfer coefficients comparable to upstream values. Upstream heating extended enhancement on the downstream heaters to larger Reynolds numbers. Higher Prandtl number fluids also extended heat transfer enhancement to larger Reynolds numbers, while a reduction in channel height suppressed buoyancy driven flows, thereby reducing enhancement. The protrusions enhanced the transition to turbulent forced convection, causing the critical Reynolds number to decrease with increasing row number. The transition region was characterized by large heater-to-heater variations in the average Nusselt number.

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Liquid Immersion Cooling of a Longitudinal Array of Discrete Heat Sources in Protruding Substrates: I—Single-Phase Convection

Direct cooling with inert, dielectric liquids may well become the technique of choice for the thermal management of future electronic systems. Due to the efficiency of phase-change processes and the simplicity of natural circulation, nucleate pool boiling is of great interest for this application.

Fundamentals of Nucleate Pool Boiling of Highly-Wetting Dielectric Liquids

By virtue of their compatibility with conventional packaging schemes, channel flows are well suited for cooling planar, multi-chip arrays. For example, chips may be mounted on one (or more) walls of a rectangular channel, while cooling is provided by flow of a liquid through the channel. Alternatively, cooling may be provided by microchannels manufactured in the chip itself. This paper focuses primarily on hydrodynamic and thermal conditions associated with liquid flow through a rectangular channel for which one wall houses an array of chips. Both single-phase mixed and forced convection cooling are considered, as are the benefits to be derived from using extended surfaces for heat transfer enhancement. Existing results provide a useful knowledge base for cooling system design, and depending on the Reynolds number, single-phase channel flows may be used to dissipate chip heat fluxes over a range from approximately 2 to 100 W/cm2. Consideration is also given to flow conditions associated with microchannels and their applicability to electronic cooling.

Application of channel flows to single-phase liquid cooling of chips and multi-chip modules

This book presents the papers given at a conference on thermal conduction in electronic components. Topics considered at the conference included an historical overview of electronics thermal control, heat pipes and immersion cooling of microelectronics, the direct air cooling of electronic components (empirical studies), the numerical analysis of air-cooled electronic components, and the thermal analysis of multichip modules and electronic components.

A. Bar Cohen

Papers

Heat transfer in electronic equipment 1986