Factors Affecting the Operational Thermal Resistance of Electronic Components

Abstract

The thermal resistance of electronic components is known to often differ considerably between standard test conditions and those found in service. One way to correct for this is to use multi-parameter thermal resistances. Another, presented here, is to adjust the junction-to-ambient thermal resistance to account for operational conditions. For forced convection applications, two factors are proposed; the first accounts for any upstream aerodynamic disturbance and the second addresses purely thermal interaction. Thus if an upstream powered component interacts with a downstream component, the two factors are combined. It is shown that both factors may be quantified in terms of readily measured temperatures and then used as coefficients to adjust the standard thermal resistance data for operational conditions. To overcome the misconception that the currently published single-value thermal resistances are solely a property of the electronic package, thermal resistance is redefined to include both the resistance of the package and the part of the printed circuit board (PCB) covered by the component thermal footprint. This approach is applied to a symmetrical array of board mounted 160-lead devices and data showing how the factors vary with component position, nondimensional power distribution and Reynolds number is presented. Based on data a new method of generating operational component thermal resistances is proposed. [S1043-7398(00)00603-4]