Comparison of CVD diamond to other substrate materials for thermal management

Numerical simulations were conducted using finite element analysis to compare the thermal efficiencies of four substrate materials-diamond, silicon, gallium arsenide and alumina. The maximum power that can be dissipated by conduction through the substrate, while maintaining a safe operating temperature in a device back-side bonded to the substrate, is determined. Two different power inputs-uniformly distributed over the entire die surface, and centered on 5% of the die area-are considered. For each power input, two different substrate cooling mechanisms-through the back side, and through an edge-are considered. Results indicate that, for cases where the substrate is cooled through the bottom and where power is concentrated over a portion of the die surface, the lateral thermal resistance of the die (and not the substrate) controls the maximum power that can be dissipated. For cases where the substrate is cooled through an edge and where power is applied uniformly over the die surface, the substrate´s lateral thermal resistance controls the maximum power that can be dissipated. The role of the solder layer in thermal management becomes important when high conductivity substrates and thin dice are used, or when voids are present