Abstract

The latest commercial applications for microelectronics use GaAs material for RF Power Amplifier devices. This leads to the necessity of identifying low cost packaging solutions with high standards for reliability, electrical and thermal performance. A detailed thermal analysis for the wirebonded GaAs devices is performed using numerical simulations. The main interest of the study focuses on the impact of die attach thermal conductivity (1.0 to 7.0 W/mK), substrate’s top metal layer thickness (25 to 50 μm), and via wall thickness (25 to 50 μm) on GaAs IC device overall thermal performance.

The study uses a 2-layer organic substrate; the die attach thickness is 15μm. The peak temperatures reached by PA stages range from 102.7°C to 113.5°C, below the prohibitive/critical value of 150°C (based on 85°C ambient temperature). The increase of die attach thermal conductivity (3 times) led to a slight decrease in peak temperatures (up to 5°C) and the decay is much larger between the cases with 1 and 2.4 W/mK. The largest temperature differences were obtained by varying the thermal via thickness, as opposed to only increasing the top metal layer thickness. The peak temperatures and corresponding junction to ambient thermal resistances are documented. It is determined that for the same die attach thickness, for a thermal conductivity larger than 7 W/mK, the impact on the PA’s peak temperature is insignificant.

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