Fabrication of SiC preform for SiC/Al composite in electronic packaging

The relationship between blend ratio (the volume fraction of larger particle size) and rheological properties of concentrated suspensions is of great importance since it is the key to obtain high solid suspensions. The rheological properties of bidisperse aqueous suspensions made of two SiC powders with different particle size (d/sub (0.5)/=1.63 /spl mu/m and 18.43 /spl mu/m, respectively) has been studied as a function of blend ratio. The results showed that the value of critical blend ratio, at which the viscosity is minimized, is in close relation to the shear rate applied. At shear rates below 10 S/sup -1/, the critical /spl xi/ was greater than 70%, but at shear rates from 10 S/sup -1/ to 500 S/sup -1/, /spl xi/ turned out to be 50%. The change of shear region from shear-thinning behavior to shear-thickening behavior may be used to account for the variation of critical /spl xi/. Dynamic oscillatory tests showed that the increment of blend ratio /spl xi/ leads to the change of suspension from nearly an elastic response to a liquid like one. It was also found that the addition of solidum metasilicate increased the strength of the SiC preform and the preform can be demolded without permanent deformation.