Thermal resistance measurements and finite element calculations for ceramic hermetic packages

An experimental and numerical characterizations of the heat transfer from a 40 pin leadless chip carrier (LCC) ceramic hermetic package (CHP) are presented. The junction-to-case thermal resistance, θ_jc, has been measured with the package bottom attached to a heat sink and with the package convectively cooled in a fluid bath. The results of these measurements are compared to the predictions of numerical finite-element calculations, and the dependence of θ_jc on the thermal properties of the package materials is discussed. For the heat sink case, θ_jc is dominated by the thermal resistances of the package ceramic and the die-attach layer. A simple analytic linear heat flow model can be used to predict θ_jc. In the case of the fluid-cooled packages, both the measurements and calculations show that θ_jc is not a very useful parameter for characterizing heat transfer from a ceramic LCC. In practical situations, the junction-to-ambient temperature drop will depend mainly on the details of the convective cooling at package surfaces