Design guidelines and synthesis of a low dielectric constant inorganic composite for high performance microelectronic packaging

This thesis is on theoretical and experimental studies of a controlled porosity inorganic composite using hollow ceramic microspheres. It evaluated the microsphere geometry issues and physical/electrical properties important to achieving a maximum reduction of the dielectric constant of the resulting composite with a minimum loss in strength. A layered sphere Bruggeman effective-medium model was developed, which describes well, the expected dielectric constant of the composite. The model incorporates the aspect ratio of the microsphere and takes into account the dielectric constant of the hollow sphere wall. While porosity reduces the dielectric constant of the composite, strength is lost with the introduction of porosity. A semi-empirical expression which incorporates an empirical strength-porosity relation and a fairly rigorous treatment of the influence of residual stresses resulting from the thermal expansion mismatch between the sphere wall and the matrix. Calculations of fracture toughness due to the residual stresses are consistent with the variation of experimental strength data. Based on these models, one may identify materials with desirable physical and electrical properties and define sphere geometries so as to maximize the reduction of dielectric constant while minimizing the attendant loss of strength. Finally, this thesis presents an emulsion/water extraction synthesis method for preparing hollow ceramic microspheres suitable for use in the composite. A phenomenological model was developed to correlate the size and aspect ratio of the hollow microspheres to the important process variables. The prediction of the model is in good agreement with the experimental observations. Feasibility and limitations of this synthesis method for preparing various compositions of small size hollow ceramic microspheres are demonstrated.U of I OnlyETDs are only available to UIUC Users without author permissio