Al/SiC carriers for microwave integrated circuits by a new technique of pressureless infiltration
Materials with high thermal conductivity and thermal expansion coefficient matching with that of Si or GaAs are being used for packaging high density microcircuits due to their ability of faster heat dissipation. Al/SiC is gaining wide acceptance as electronic packaging material due to the fact that its thermal expansion coefficient can be tailored to match with that of Si or GaAs by varying the Al:SiC ratio while maintaining the thermal conductivity more or less the same. In the present work, Al/SiC microwave integrated circuit (MIC) carriers have been fabricated by pressureless infiltration of Al-alloy into porous SiC preforms in air. This new technique provides a cheaper alternative to pressure infiltration or pressureless infiltration in nitrogen in producing Al/SiC composites for electronic packaging applications. Al-alloy/65vol% SiC composite exhibited a coefficient of thermal expansion of 7/spl times/10/sup -6/ K/sup -1/ (25/spl deg/C-100/spl deg/C) and a thermal conductivity of 147 Wm/sup -1/K/sup -1/ at 30/spl deg/C. The hysteresis observed in thermal expansion coefficient of the composite in the temperature range 100/spl deg/C-400/spl deg/C has been attributed to the presence of thermal residual stresses in the composite. Thermal diffusivity of the composite measured over the temperature range from 30/spl deg/C to 400/spl deg/C showed a 55% decrease in thermal diffusivity with temperature. Such a large decrease in thermal diffusivity with temperature could be due to the presence of micropores, microcracks, and decohesion of the Al/SiC interfaces in the microstructure (all formed during cooling from the processing temperature). The carrier showed satisfactory performance after integrating it into a MIC.
Aluminum Silicon Carbide (AlSiC) For Cost-Effective Thermal Management And Functional Microelectronic Packaging Design Solutions
Aluminum Silicon Carbide (AlSiC) metal matrix composite (MMC) materials have a unique set of material properties that are ideally suited for electronic packaging applications requiring thermal management solutions. The AlSiC coefficient of thermal expansion (CTE) value is compatible with direct IC device attachment for the maximum thermal dissipation (AlSiC thermal conductivity 170 – 200 W/mK). The low material density of AlSiC (3 g/cm) makes it ideal for weight sensitive applications such as portable devices over traditional thermal management materials such as CuMo (10 g/cm) and CuW (16 g/cm). Structural packaging requirements are satisfied by the material strength and stiffness that are both approximately three times greater than Al-metal. Additionally, AlSiC is a hermetic material that can be used to give protection to environmentally sensitive electronic components. Also, this composite material is electronically conductive providing EMI/RFI shielding. The AlSiC material and functional electronic packaging geometries are produced using Ceramics Process Systems Corporation's QuickSetTM/QuickCastTM net-shape fabrication process. This net-shape packaging fabrication process is capable of producing complex geometrical packaging features without the need for costly machining. Additionally, functional packaging features such as feedthrus, sealrings and dielectric substrates are incorporated in AlSiC during fabrication using the CPS Concurrent IntegrationTM technique eliminating the need for the traditional assembly and brazing or soldering operations. The ideal AlSiC material properties coupled with net-shape fabrication and Concurrent IntegrationTM processes cost-effectively provide high-performance thermal management solutions in functional packaging designs. This paper will review the AlSiC material properties contrasted to traditional heat-sinking materials. AlSiC fabrication processing flow will also be reviewed and discussed. Functional packaging designs and application solutions will be illustrated through CPS AlSiC product examples.
Developments in the processing and properties of particulate Al-Si composites
In the past ten years, materials R&D has shifted from monolithic to composite materials, adjusting to the global need for reduced weight, low cost, quality, and high performance in structural materials. This article reviews developments in the molten processing of particulate Al-Si alloy composites and their respective properties. Existing and emerging processing innovations are discussed, and the reinforcement phases in prominent R&D activities are identified. The vortex (or mixing) method continues to be the most popular processing method in use because of its ease of operation, total production cost, and suitability, while the infiltration, compocasting (or rheocasting), in-situ, and spray atomization and codeposition techniques receive less attention.