Development of low thermal expansion - high conductivity nanocomposites.

摘要

Heat dissipation and thermal expansion mismatch are important issues in many electrical and electronics applications. The thermally induced stresses that arise due to poor thermal management and the thermal expansion mismatch among different board materials can lead to premature failure of electronic assemblies. The solution to the heat dissipation and thermal mismatch problems may lie in the development of low thermal expansion, high conductivity materials. Materials such as Cu-Invar, Cu-Mo, and various metal-ceramic composites have successfully been employed in applications such as heat sinks and core constraining layers in circuit boards, but many of these materials have specific limitations such as high processing costs and anisotropic properties.; Homogeneous alloys with intimately mixed components may offer the desired thermal and electrical properties at manufacturing costs much lower than those of the materials currently in use. In addition, homogeneous alloys produced by chemical synthesis and powder processing techniques can offer isotropic thermal, electrical, and mechanical properties, which may be of benefit for future applications where low coefficient of thermal expansion (CTE) and high conductivity are desired.; In this dissertation, novel solution-based synthesis techniques aimed at the production of nanocrystalline alloys and composites are explored. Low thermal expansion, high conductivity materials such as Cu-Fe-Ni, Cu-Mo, Ag-Mo and Ag-Fe-Ni are chemically synthesized, processed, and characterized. In most of the systems investigated, homogeneous alloys of a high conductivity phase and a low CTE phase were produced.; The Fe and Ni in the Cu-Fe-Ni system combined to form a low CTE Invar-like phase, and CTE values for Cu-Invar alloys ranged from 17.3 × 10 −6°C−1 for pure Cu to 1.85 × 10−6°C−1 for Invar. The electrical and thermal conductivity of the Cu-Fe-Ni alloys, however, was low due to the incorporation of Fe and Ni into the Cu-rich phase. Aging heat treatments caused only marginal improvements in the conductivity of the Cu-Fe-Ni alloys.; Cu-Mo, Ag-Mo, and Ag-Fe-Ni alloys exhibited improved conductivity compared to the ternary Cu-Fe-Ni alloys as a result of lower solute contents in the high conductivity (Cu) and (Ag) phases, and the thermal expansion values in these systems were close to rule of mixtures approximations. Metal-aluminum borate ceramic systems were also investigated, but samples with high sintered densities were not obtained due to metal-ceramic phase incompatibility.