A cross section of the iCoupler planar transformer die is shown here. On the top is a gold coil that has been applied to the polyimide insulation. Below the polyimide insulation is the bottom coil which is made from the top metal of the CMOS process. The key to the high voltage isolation performance for iCoupler digital isolators is the thick 20 micron polyimide insulation. The polyimide is a uniform low-stress, thick-film layer that is applied to the CMOS wafers in a clean room environment in a low-cost high-volume standard IC process. The 20 micron of iCoupler polyimide is rated for a working voltage of 400 volts RMS for 50 years and a surge rating of greater than 10kV meeting VDE reinforced isolation requirements which no thin film silicon dioxide integrated isolator technology can achieve. Polyimide provides large breakdown strength, high thermal and mechanical stability, excellent chemical resistance, good ESD performance and low relative permittivity. The physical dimensions for the iCoupler transformer isolation provides Common-mode transient immunity which is 2 to 3 times better than what can be achieved with optocouplers. These polyimide based iCoupler solutions have been in volume production since 2001 and have shipped over 600 million channels of isolation to thousands of customers providing a high level of reliability in a wide variety of applications.