**2.8 Controlling the thickness**

The thickness of the casted PI film depends on several factors such as the viscosity, molecular weight of the PAA solution, and the spin speed of spin coater. Varying PI film thickness in the range of 10–150 μm can be achieved by using a spin coating method. Two different viscosity solutions of PAA are used to obtain PI films as shown in **Figure 8**. The film thickness decreases with increasing spin rate. To avoid the bubbles and the accumulation of excessive blocks of PAA solution, spin cycle time should increase because prolonger spin times improve film coating uniformity, but at the same time, it can reduce the film thickness.
