Proposal for thermal evaluation for high density mounting technology

On high-density-mounting circuit boards, heat generated in the junction of the VLSI IC flows through the package to the printed-circuit card, heats up the lead pins of the surrounding VLSIs, and raises their junction temperature T_j. The conventional thermal resistance between the junction and ambient air, θ_j-a, cannot be used to estimate these thermal effects. A quantity representing the thermal resistance between the junction and the surface, θ_j-s, which can deal with these effects, is proposed. An analysis approach that allows T_j of surface-mounted devices to be predicted using measured surface temperatures is described. Experimental results that are in good agreement with theory are presented