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.
Metal-matrix composites for space applications
From the onset of the space era, both organic-matrix and metal-matrix composites (MMCs), with high specific stiffness and near-zero coefficient of thermal expansion (CTE), have been developed for space applications. Of the organic-matrix composites, graphite/epoxy (Gr/Ep) has been used in space for truss elements, bus panels, antennas, wave guides, and parabolic reflectors in the past 30 years. MMCs possess high-temperature capability, high thermal conductivity, low CTE, and high specific stiffness and strength. Those potential benefits generated optimism for MMCs for critical space system applications in the late 1980s.1,2 The purpose of this article is to detail the history, status, and opportunities of MMCs for space applications.
Using Activity Theory in Developing Instructial Tools for Project Management Studies
Competence and skills of the project manager are significant to project success. The skills needed in project managersâ work cannot be learned only by reading the books or a lecture hall; one learns them by practice. Therefore, an important challenge for educational institutions is to develop pedagogical practices that allow students to participate in working life projects and to confront real-life problems. Project-based learning (PBL) offers a model that enables students to practice the skills and competences needed in working life projects by utilizing real-world work assignments in time-limited projects. Using PBL method alone does not necessarily guarantee learning result. In order to be successful, PBL method requires effective and competent supervision and guidance of students as well as appropriate tools for instruction. In this study the concepts from activity theory (AT) are applied to development tools for supervising project-based learning.