Pierre-Marie Geffroy1, Jean-Frangois Silvain2 and Jean-Marc Heintz2
1CNRS, Science des procedes ceramiques et de traitements de surface, Limoges 2CNRS, Institut de la Chimie et de la Matiere Condensee de Bordeaux
France
1. Introduction
Carbon fibres reinforced copper matrix composites (Cu/C composites) offer an excellent thermal conductivity and a low coefficient of thermal expansion. Then, these composites are compromising heat dissipation materials for electronic application.
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The modern electronic devices consist of a variety of metallic, ceramic, plastic or composite components. The large difference of coefficient of thermal expansion (CTE) between ceramic substrates, such as Al2O3 and AlN, and heat dissipation materials, such as Cu and Al, and Si and GaAs semiconductors, induces thermal stresses resulting in failures at the interfaces between the different layers of the devices (fig. 1). In high power dissipation packages, thermal management is an important issue to prevent thermal damage of sensitive components on the silicon ship, especially for high density electronic packaging. Thermal management is thus one of the critical aspects in design of multichip modules to ensure reliability of electronic devices with high packing and power densities. In this context, there is an increasing demand of new heat dissipation materials having low CTE combined with high thermal conductivity, such as Cu/C composites.
Heat sink
Fig. 1. Design of microelectronic devices with peak stress in solder joint.
thermal conductivity, such as Al/SiC or Cu/W composites, have improved the reliability of electronic devices [Luedkte, 2004]. However, these composites are often too expensive for many applications. In addition, their machinability and the elaboration of thin sheets remain still very difficult and expensive.
Carbon fibres reinforced copper matrix composites corresponds to a good compromise between thermo mechanical properties and thermal conductivity [Korb et al., 1998]. Their main advantages are the following properties (Table 1):
i. lower density than copper,
ii. very good thermal conductivity,
iii. low coefficient of thermal expansion,
iv. good machinability.
Other advantages of copper/carbon fibre composites are adaptive thermal properties, which can be adjusted with the nature and the volume ratio of carbon fibres.
|
Function |
Materials |
CTE 10-6 °С-1 (RT- 250°C) |
Thermal conductivity W. m-i. K-i at 25°C |
Density |
|
Chips |
Si |
4.2 |
150 |
2.3 |
|
GaAs |
5.9 |
45 |
5.32 |
|
|
Heat sinks |
Copper |
17 |
400 |
8.95 |
|
Aluminum |
23 |
230 |
2.7 |
|
|
Aluminum /63 % SiC |
8 |
165 |
3 |
|
|
Copper/85 % W |
6 |
180 |
17 |
|
|
Copper /40 % Carbon fibres (Pitch) |
17 1 9-12 // |
140-160 1 > 210 // |
6.11 |
|
|
Substrates |
Al2O3 |
6.7 |
20-35 |
3.9 |
|
AlN |
4.5 |
170-250 |
3.26 |
|
Table 1. Properties of different electronic device materials (//: in plane properties; 1: through-thickness properties). |
The purpose of this chapter is to present the main research results during this last decade on the elaboration and properties of Cu/C composites. First, the different elaboration route of Cu/C composites is presented in this chapter. Then, the main physical properties of Cu/ C composites are discussed, and a particular attention is given on the improvement of interface copper/carbon and thermal properties of Cu/ C composites. Finally, the main potential applications of Cu/ C composites are introduced, and their performances in focused applications are discussed at the end of the chapter.
