A General Method for the Connection of a Component Thermal Model to a Board

Abstract

In this paper, a generalized method for the connection of a thermal component model in board-and system-level thermal simulations is presented. The method allows for the definition of uniform heat flow connections as well as the standard uniform temperature interface regions. The use of uniform heat flow ports will be shown to better handle cases where large temperature gradients are present in the base model. The two methods of connecting the component model will be evaluated using two different models. First, a simple example will be presented to illustrate the nonphysical behavior introduced by the use of uniform temperature connections. Second, a model of an electronic package will be used to evaluate the relative merits of the two connection methods with respect to board thermal conductivity and boundary conditions present on the board and the package. It will be shown that the results from use of uniform heat flow connections are generally better than from use of uniform temperature regions with respect to predicting junction and board temperatures.

Algorithmic Approach for Thermal Port Definition

“…Referring to definitions given in [4], the equations describing board or component model present a thermal network characterizing a numerical thermal model in steady-state condition. Therefore, the equation for the board model including port heat fluxes to the linking nodes is (1) where is the thermal conductance matrix, is the vector of unknown temperatures (including linking nodes), is the source vector of internal power generations and boundary conditions, and is a selector matrix that maps the port currents of the component model into the board model.…”

“…Solving (2) for and substituting into (3), the expression for the heat flow through ports in terms of the port temperatures is found (4) Further, by defining an attachment conduction matrix and a source vector in the form…”

“…As explained in [4], the solution of (1) with and being added into is associated with the augmentation of the lefthand-side matrix by dense and matrices and the righthand side by . This augmentation might slow down the solution, or make it even impossible-primarily when large number of ports are considered into the component model.…”

“…These ports provide thermal links and heat exchange between components. Successful modeling of such a thermal link mainly depends on: 1) thermal port geometry and configuration [1], [2], where a careful selection of these parameters might accomplish high accuracy in the range of 5% [3] and 2) the method of connection [4]. As shown in [1]- [5], a commonly used connection method is based on the assumption of a uniform temperature (UT) across each port region.…”

“…A more general formulation of connection methods was presented in [4], where the use of uniform heat flow (UHF) ports allows temperature variation within the port surface, thus permitting good predictability even in cases with higher degree of nonuniformity in temperature distribution. It was concluded that UHF ports are generally superior to UT ports.…”