Thermal Performance Comparison and Metallurgy of Direct Copper Bonded AlN, Al2O3 and BeO Assemblies - ISHM '92 Proceedings

Description

Presented is a direct empirical comparison of direct bonded copper (DBC) Al2O3, AlN and BeO. A packaging structure incorporating a field effect transistor mounted onto two-sided DBC ceramic was fabricated with thermocouples carefully placed to measure the temperature difference between the top chip surface and bottom of the metalized-substrate. A 2D computer simulation was used to predict the ideal thermal conductivity of a substrate layer for a given temperature difference. The measure and predicted temperature differences were compared, and a resulting equivalent thermal conductivity (Ke) was determined which included interfacial and void effects. Results show that BeO has a substantially higher Ke than AlN at 8°C but both have lower values at 27°C due to the strong inverse temperature dependence of Ke. The Ke for Al2O3 actually increases from that at 27°C because of heat spreading in the thick metalization. The Ke is the actual value a designer should use for the ceramic at the corresponding operating temperature.