The trend in electronic circuits and modules, especially for power electronics, is to a higher level of miniaturization at higher power densities. Due to this fact thermal management has become one of the most important keywords in the electronics industry in recent years. The heat dissipation of power semiconductors like IGBTs and MOSFETs can lead to circuit damages. As a consequence thermal aspects have to be considered when electronic systems are designed. The selection of materials plays an important role regarding packaging, and even the thermal behaviour of heatsinks is taken into account. Metals are the materials of choice in conventional systems, at which aluminium and copper are most frequently used due to their relatively high thermal conductivity. However, aluminium and copper have the disadvantage of a high CTE (coefficient of thermal expansion), which becomes an important factor in case of thermal cycling. Contrary to this, semiconductors like silicon have a very low CTE so that the combination of these materials with their significantly different CTE results in mechanical stresses that can cause fatal damages to the devices. This problem can be solved by using expansion controlled heatsink materials with high thermal conductivities like aluminium-graphite composites.