Thermal management enhancement for GaAs devices using CVD diamond heat spreaders in a plastic package environment

Long term package reliability is becoming an increasing concern as IC clock speeds and power densities increase while simultaneously the package foot print decreases. Significant contributors to increasing the reliability and performance of plastic packages are reducing the package/junction temperature (Tj) and improving the integrity of the interfaces between the encapsulating polymer and the constituent package materials. CVD diamond, with its superior thermal conductivity, low density and high electrical resistivity offers an attractive alternative to traditional metal heat spreader materials to insuring a low junction temperature and therefore long time between failures. Considering these goals and the ubiquitous performance, reliability, and economic requirement, GaAs devices were encapsulated in a plastic package with CVD diamond substrates as the thermal management platform. Both GaAs flip-chip with polymer underfill and conventional face up chip-wire configurations were evaluated. This paper will highlight the effect of chemical termination of the CVD diamond surface on encapsulant polymer adhesion using x-ray photoelectron spectroscopy, surface energy measurements, and boiling water immersion/peeling tests. Additionally, the enhanced thermal and reliability (mechanical/environmental) performance of plastic packaged GaAs devices using "optimally terminated'' CVD diamond will be discussed.