Memory budget and peripheral set
With 8 KB of RAM and 16 KB of Flash, the firmware footprint is tight — this part is sized for a single control loop, a Modbus RTU slave, or a BLE coexistence handler, not a full RTOS with a TCP/IP stack. The 1 KB EEPROM is a genuine hardware block (not emulated Flash) that survives 100k write cycles, which simplifies field-calibration and configuration storage.
The STM32L031G4U6 comes in a 28-pin UFQFPN package measuring 4 mm × 4 mm — a compact, thermally efficient land-grid array with an exposed pad for heat sinking. The 21 I/O lines are enough for a handful of sensor inputs, a serial display, and a few control outputs, but you won't have spare pins for a parallel memory bus or a large switch matrix.