Materials for thermal management of electronic devices

Thermal aspects are becoming increasingly important for the reliability of the electronic components due to the continuous progress of the electronic industries such as the higher output power and the higher level of integration of ICs. To achieve long life and reliable performance of these components, it is necessary to keep the operating temperature of the electronic device within specified limits. Therefore, the effective thermal management is a key issue for packaging of high performance semiconductors. It can be realized by active or passive cooling methods. In the case of passive cooling materials working as heat sink and heat spreader should have a CTE of 4-8 ppm/K and a high thermal conductivity. This paper will review the recent developments of copper matrix composites reinforced with diamond or graphite in order to obtain a composite material having a thermal conductivity higher than 400W/mK in case of copper/diamond and copper/graphite. The Cu-based composites were fabricated by a powder metallurgical method (powder mixing with subsequent pressure assisted consolidation). In order to design the interfacial behaviour between copper and the reinforcement different alloying elements were added to the copper matrix. The thermophysical properties will be displayed and discussed as a function of the reinforcements as well as the alloying elements used for composite preparation. Additionally active cooling methods using thermoelectric materials (Pelletier cooling) can also be realized. The main challenge is to improve the thermoelectric properties (figure of merit - ZT) as well as mechanical properties. Today thermoelectric nanocomposites with remarkably improved properties can be produced via thin film technologies. In this paper recent results of the preparation of polycrystalline thermoelectric materials based on Bi2Te3 will be presented. The manufacturing technique is based on the preparation of powders via milling of melt ingots and subsequent sintering using spark plasma sintering as a fast sintering technique to get polycrystalline bulk materials. Properties will be presented and compared with conventional single crystals used up to now.