Various physical parameters of solvents within two component, PMMA + Solvent films are analyzed for their impact upon the coating uniformity of spin deposited PMMA films. Towards this end, a model is presented for describing the surface behavior of spin-on films during the latter stages of deposition, correlating the tendency of a film toward non-uniform deposition to physical characteristics of the spin-on solution. A finite difference solution to this model is presented for two-component, spin-on films that is shown to effectively predict the uniformity of the resulting thin-film layers. The model is then used to determine the impact of specific film parameters upon the predicted spin-on uniformity of the film. Based upon these results, the interdependency between evaporation rate, solvent viscosity, surface tension and rotation rate in determining the uniformity of the spin-on film is evaluated by comparing the model predictions against those found in actual spin-on, two component films. The results from this model are used to provide a physical explanation for why certain surface non-uniformities begin to develop during spin coating.