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Research Papers

# Integrating Compact Thermal Models in CFD Simulations of Electronic Packages

[+] Author and Article Information
Rohit Dev Gupta1

Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208 016, Indiarohitdev@iitk.ac.in

Vinayak Eswaran

Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208 016, Indiaeswar@iitk.ac.in

1

Also at Dell India R&D Center, Bangalore, India.

J. Electron. Packag 130(2), 021002 (Apr 15, 2008) (9 pages) doi:10.1115/1.2837511 History: Received July 26, 2006; Revised July 10, 2007; Published April 15, 2008

## Abstract

Compact thermal models (CTMs) are simplified multi-nodal thermal resistor network representations of the detailed material and geometric structure of the electronic package. CTMs predict the thermal response of the package, in various environments, to within an accuracy of 2%. The junction temperature of the package is typically obtained by solving the linear algebraic network equations of the CTM, with the heat transfer to the ambience modeled by a convection coefficient obtained from handbooks, assuming identical ambient conditions imposed on all nodal surfaces. This approach may give misleading results as the ambience at each nodal surface can differ depending on the cooling flow patterns at that surface. In this work, a methodology is presented where the network equations of the CTM are integrated into the governing fluid flow and energy equations solved by computational fluid dynamics (CFD). The $CTM+CFD$ approach predicts a significantly (20–30%) higher junction temperature as compared to the conventional CTM network solver method, even when the convection coefficient used in the latter case is obtained more accurately from CFD, rather than from handbook correlations. It is also found that CFD computations assuming uniform flux at the package surfaces (and ignoring the internal resistance of the package) vastly under-predict the junction temperature. The new approach offers a promising alternative for electronic package thermal design and is highly advantageous where the internal geometric and material configurations are not known due to proprietary concerns.

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## Figures

Figure 1

Representation of a typical CTM

Figure 2

Cross-sectional diagram of MLF package (13)

Figure 3

CTMs of MLF package: (a) star network topology and (b) shunt network topology

Figure 4

(a) Schematic diagram of the channel with electronic package and (b) a shunt network CTM of the package, as used in the present study

Figure 5

Validation of present solver with benchmark solution of (a) Ghia (23) and (b) Moallemi (24)

Figure 6

Exit temperature profiles of air stream for different BCs

Figure 7

(a) Streamlines and (b) velocity profiles in the flow domain

Figure 8

Isotherms around the package for different BCs: (a) uniform flux, (b) star network, and (c) shunt network

Figure 9

Variation of surface temperature along package surface for constant flux case, CTM with star network, and CTM with shunt network

Figure 10

Comparison of (a) junction temperature, (b) average surface temperature, and (c) average heat dissipation for different package surfaces at Re=200

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