84 MHz Cortex-M4 in a 49-ball WLCSP
The STM32F401CCY6TR is an STM32F4-series ARM Cortex-M4 microcontroller in a 49-WLCSP package, rated for 84 MHz operation. This part is typically specified for space-constrained designs where a full LQFP package won't fit, such as wearable sensors, portable instrumentation, or compact IoT nodes.
The 64 KB SRAM is shared between code data and DMA buffers; if your application uses USB OTG with double-buffered endpoints, budget at least 8 KB for the USB FIFO. The 10-channel 12-bit ADC (10x12b) is adequate for reading a handful of analog sensors, but don't plan on simultaneous sampling — it's a single SAR with a mux.
The base product number STM32F401 covers a range of Flash and SRAM densities in the same WLCSP footprint, so if a project later needs more memory, a pin-compatible upgrade within the family is possible without a board spin.
49-WLCSP — what the package means for assembly
The 49-WLCSP (Wafer-Level Chip-Scale Package) has no leads — the solder balls are directly on the die. The 0.4 mm ball pitch demands a Class 3 PCB capability for reliable solder joints; a standard 0.5 mm pitch board house may struggle with yield. For rework, a hot-air station with a fine nozzle and a preheat plate is needed — a standard soldering iron won't touch it.