The STMicroelectronics STM32L412TBY6TR is a 32-bit ARM Cortex-M4 MCU from the STM32L4 ultra-low-power series, clocked at 80 MHz with 128 KB Flash and 40 KB SRAM. The 36-ball WLCSP (2.58 x 3.07 mm) saves significant board area compared to a QFN, but requires a controlled SMT process and underfill if the board sees vibration or thermal cycling.
Memory and peripherals — fitting the firmware and the bus
The WLCSP package's solder-joint reliability at temperature extremes depends on the PCB's coefficient of thermal expansion — a board with a matched CTE or a small die-to-board ratio is recommended for repeated -40°C cycles.