Evaluation of the thermal and hydraulic performances of a very thin sintered copper flat heat pipe for 3D microsystem packages

EVALUATION OF THE THERMAL AND HYDRAULIC PERFORMANCES OF A VERY THIN SINTERED COPPER FLAT HEAT PIPE FOR 3D MICROSYSTEM PACKAGES

Slavka Tzanova1, Lora Kamenova2, Yvan Avenas2, Christian Schaeffer2

1Technical University of Sofia, 2INP Grenoble

ABSTRACT

The reported research work presents numerical studies validated by experimental results of a flat micro heat pipe with sintered copper wick structure. The objectives of this research were to produce and demonstrate the efficiency of the passive cooling technology (heat pipe) integrated in a very thin electronic substrate that is a part of a multifunctional 3-D electronic package. The enhanced technology is dedicated to the thermal management of high dissipative microsystems having heat densities of more than 10W/cm2. Future applications are envisaged in the avionics sector. A 2D numerical hydraulic model has been developed to investigate the performance of a very thin flat micro heat pipe with sintered copper wick structure, using water as a refrigerant. Finite difference method has been used to develop the model. The model has been used to determine the mass transfer and fluid flow in order to evaluate the limits of heat transport capacity as functions of the dimensions of the wick and the vapour space and for various copper spheres radii.

1. INTRODUCTION

Stacking electronic substrates in 3D packaging allows creating compact, lightweight and multifunctional electronic modules. This conception answers the main requirement of miniaturization of the electronics market and plays a key role in the microelectronics nowadays. Every configuration has specific thermal constraints and requires the implementation of adapted cooling techniques.
The reported research work presents numerical studies validated by experimental results of a flat micro heat pipe with sintered copper wick structure. The objectives of this research were to produce and demonstrate the efficiency of the passive cooling technology (heat pipe) integrated in a very thin electronic substrate that is a part of a multifunctional 3- D electronic package [1].

2. METHODOLOGY

The importance of the electronics cooling in the avionics sector continues to remain substantial due to ever-improving microelectronics technologies and the consequent elevated power consumption density. The reported research work involves the investigation of thermal solutions for a double sided substrate, part of a multifunctional 3-D electronic module (Figure 1). The objective is to integrate heat pipes into the double-sided electronic slices in order to satisfy the requirements for the power dissipation. Heat pipes have proven their efficiency for many applications where high heat fluxes suppress the possibility of applying conventional cooling systems [2]. Sintered copper spheres have been used for the capillary wick structure and pure water as a working fluid. Numerical investigations have been performed under steady-state conditions in order to optimize a first fabricated in the laboratory copper flat heat pipe. In detail, this paper aims to provide 2D hydrodynamic model [3], [4] for simulating the performance of the heat pipe system. Mathematical formulation of the equations that govern the physical laws inside the heat pipe is also presented. The numerical solution of the 2D model is further validated by experiments and has shown better promise over the one-dimensional models. ©EDA Publishing/DTIP 2007 ISBN: 978-2-35500-000-3

Slavka Tzanova, Lora Kamenova, Christian Schaeffer Evaluation of Thermal and Hydraulic Performance of Flat Heat Pipe for 3D Microsystem Packaging

Figure 1 Double sided substrate with integrated heat pipe

3. HEAT PIPE DESCRIPTION

The schematic diagram of the thin flat heat pipe is illustrated in Fig. 2. It consists of three basic sections - evaporator, condenser and adiabatic. Applying heat to the evaporator surface causes the liquid to vaporize. Subsequently, the pressure build-up entrains the vapour to move through the adiabatic section into the condenser, where it condenses. The liquid is then driven back to the evaporator by the capillary effect of the wick structure. Thanks to the isothermal characteristics of the vapour, there is a very small temperature gradient between the hot and the cold sections. In the presented model, the hot and the cold sources are applied as shown on Fig. 2. The total length of the heat pipe is 44 mm; its width – 30 mm and height – 2.6 mm.
The wick structure within the heat pipe provides the capillary pressure needed for the return of the liquid from the condenser to the evaporator. To achieve maximum heat transport through the heat pipe, the geometry of the wick must be optimized. This requires trade-offs between different considerations. The maximum capillary pressure generated by the wick

…(Full text truncated)…