The electronic industry is involved in an endless search of new materials that enable electronic systems with increasing density of components, through higher heat dissipation capability, lower density, higher reliability while matching the CTE of materials currently used in electronic packaging components, ceramic substrates, Si, SiC and other semiconductors, etc. In fact, reliability appears nowadays as is one of the major problems that affect the electronics, microelectronics, telecom, automotive, and aeronautic industries. Especially, thermal management is an increasingly critical part of achieving competitive functionality in these industries since it impacts speed, size, weight and reliability of components, mainly for future components which will need to dissipate heating from electric currents and packaging densities in order of magnitude higher than those in use today. Due to the high power dissipation capability of the current and future electronic semiconductors and high reliability demand, it is mandatory to develop a new electrical conductive layer based on Cu/C functionally graded materials with adapted CTE in order to adjust the thermal stresses between the FGM ceramic and the Si wafer.
Cu/C composites are so attractive materials for thermal conduction because of its high thermal conductivity and low CTE. Their potential primary applications are heat sinks, thermal planes, and substrates (fig. 17).
Fig. 17. Two examples of machined C/Cu composite materials for a) railroad application and b) aeronautic application
4. Conclusion and outlooks
The properties of Cu/C composites depend mainly on conditions and routes process. Today, the powder metallurgy processes offer Cu/C composites with a low cost of elaboration, a low CTE and excellent thermal conductivity properties. However, physical properties obtained by power metallurgy process such as CTE and thermal conductivity are strongly anisotropic. In additional, the lack of interfacial strength between copper and carbon requires a previous surface treatment of short carbon fibres in order to improve the interface properties between copper matrix and carbon fibres. Recent research developments suggest that the thermal conductivity of these composites materials should be largely improved by using nanofibres with a higher thermal conductivity than copper (up to 400 W. m-1.K-1).