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Experimental data confirm the utility of the following simple equation in predicting the spin coating behavior of polyimide precursor solutions: in which c PI h k t =time, and: w h = CPokP1wP2tP3 (1) = polymer solution solids weight fraction: = fitted coefficient (Greek letter beta); = film thickness after cure or solvent removal: = polymer solution kinematic viscosity, centistokes; = wafer spin speed, rpm (Greek letter omega). SPIN SPEED WAFER < VISCOUS DRAG > CENTRIFUGAL FORCE I POLYMER ! SOLUTION WAFER h = FILM THICKNESS AT TIME t dh = DIFFERENTIAL FILM THICKNESS OF A FLUID ELEMENT m. I. Fluid mechanics, viscous laminarflow.

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The following models describe the effect of temperature and shear rate on the viscosity of polyisoimide solutions.Data was obtained for 20, 30, and 40% polyisoimide solutions in 20:80 tetrahydrofuran/diglyme and for a 30% solution in N-methyl-pyrrolidone at temperatures of 25". 35". 55", and 75°C. The measurements were taken on a Brookfield cone and plate viscometer at shear rates ranging from 9.59 to 383.4 reciprocal seconds. Experimental data fits model (1) reasonably well. In some cases, model (2) provides a better fit. This model accounts for temperature dependencies in the power law shear-thinning exponent.The coefficients p depend on the material lot that is being tested even though the lot molecular weights are very close. Slight differences in acid functional group concentrations for this particular material are a possible explanation.