Mikroe MCU CARD for STM32 STM32F405ZG allows very simple installation and replacement of the microcontroller unit (MCU) on a development board. The new MCU Card standard ensures the absolute compatibility between the development board and any of the supported MCUs, regardless of their pin number and compatibility. MCU Cards are equipped with two 168-pin mezzanine connectors, allowing them to support even MCUs with extremely high pin count. Their clever design allows very simple usage, following the well-established plug & play concept of the Click board™ line.