Question: What should be the Hardware and Firmware precaution to protect CapSense Button
Firmware precaution has been taken in CSD and CSA user module code, so there is no need to take any extra precaution in firmware.
PSoC pins provides protection against ESD up to 2KV. Using thicker overlay high level of ESD protection can be achieved. But thicker overlay also reduces the sensitivity of CapSense. Please find the minimum thickness required to withstand 12KV ESD for different overlays material on page 8 of attached application note.