To reduce the Current consumption I decided to design a RTC into my design. 

This RTC can disable the complete Power supply with an MOSFet.

With this little trick the Quiescent current drops dramtically when the keyboard is not in Use.

According to the datasheet this leads to a low current of 50nA when the design is not in use.

This RTC Chips wakes up based on the the resistors designed around the Delay Pin.

With this Resistors you define the sleep period between the Mikrocontroller shall not get any POWER

Once operation of the keyboard is finished the Microcontroller can send a "Done" Signal to the RTC to send it to sleep earlier than defined by the resistors.