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Question: What is the maximum overlay thickness for CapSense® sensors?
There is no specific maximum value for overlay thickness. You should select the overlay material and thickness depending on the following factors:
The sensitivity of your CapSense system is directly proportional to the overlay material and thickness.
Cfinger = (εo εr A) / D
εo = free space permittivity
εr = dielectric constant of overlay
A = area of finger and sensor pad overlay
D = overlay thickness
A thicker overlay lowers finger capacitance, which in turn lowers finger response. A thicker overlay can also increase parasitic capacitance. However, the overlay must be thick enough to prevent breakdown during an ESD event. Remember that you can increase finger response by increasing button size to compensate for thicker overlays. The following table gives the minimum overlay thickness for different materials.