| Si_p/Al composite has been widely concerned as a new kind of electronic packaging material for its excellent comprehensive properties, such as low density, high thermal conductivity, low thermal expansion coefficient which can be controlled. Si_p/Al composite not only is more machinable than SiCp/Al composite but also has good welding property.The Si_p/Al electronic packaging materials were fabricated by dry-pressing molding and vacuum gas pressure liquid metal infiltration. How the binders affect Si preform's bend strength and how to adjust the porosity of the preform were studied. The variability of the microstructure and property of the Si_p/Al composite with the process of the vacuum gas pressure infiltration and the hot treatment were also studied. The effects of the oxidized, nitrified and carbonized treatments of Si performs on the properties of the composite were investigated for the first time. Conclusions are drawn as follows:(1) Si preform green bodies were achieved by using the three kinds of binder mixtures: polycarbosilane and paraffin mixture, polysiloxane and ethyl cellulose mixture, and acid phosphate and polyvinyl alcohol mixture (including acid phosphate and amyloid mixture). Preforms fabricated by polycarbosilane and paraffin mixture had the highest bend strength.(2) It was found that the porosity in Si preform decreased with the increasing of the molding preasure, and the change came to slow as the pressure increase. Under 80MPa molding preasure, the volume of Si_p/Al composite decreased 10% when 30% amyloid or Al powder were blended into Si powder. The volume of Si_p/Al composite could be adjusted between forty percent and sixty percent.(3) The extend of Si perform resolved into molten Al, which affected the dimension, the microstructure and the properties of Si_p/Al composite decreased with the decrease of the liquid aluminum and the perform temperature and the increase of the amount of Si in Al matrix during the process of the vacuum gas pressure infiltration.(4) The hermeticity and the thermal expansion coefficients of Si_p/Al composite did not changed a lot, while thermal conductivity increased, with the extend of Si perform resolved into molten Al. The thermal conductivity of Si_p/Al composite would decrease obviously, if the microstructure of Si_p/Al composite were affected seriously. The bend strength decreased with the increase of the Si particles'dimension.(5) The configuration evolution of Si particle in Si_p/Al during 420℃heat treatment was as follows: the corners and edges of the silicon particles dissolved, the small silicon particles disappeared and the big silicon particles became bigger and reticular. It was also discovered that, after heat treatment at 420℃for one hour, the hermeticity of Si_p/Al composites did not change obviously, while the bend strength, thermal conductivity and coefficients of thermal expansion of the composite decreased obviously; after heat treatment at 600℃for four hours, the lacunae in Si_p/Al composites increased obviously, which greatly affected the properties of the composites.(6) When the performs were oxidated at 1100℃for one hour, the thermal expansion coefficients and the bend strength of Si_p/Al composite did not change a lot, but the thermal conductivity decreased about fifteen percent.(7) When the performs were nitrified at 1200℃for one hour, the thermal conductivity and the bend strength of Si_p/Al composite increased, while the hermeticity and the thermal expansion coefficients did not changed a lot. But the thermal conductivity of Si_p/Al composite decreased obviously, when the performs were nitrified at 1200℃for three hours or 1300℃for one hour.(8) When the performs were carbonized at 1300℃for one hour, the thermal conductivity and the bend strength of Si_p/Al composite increased, while the hermeticity and the thermal expansion coefficients did not changed a lot. The thermal conductivity of Si_p/Al composite decreased obviously, when the carbonized time was prolonged to three hours. |
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