This is the official flag that ST has stopped actively promoting this exact WLCSP variant for new production builds. For an existing BOM line, this means the part remains available through the independent channel for ongoing production support, but any new board spin should target a current-recommended STM32F4 device. The NRND status does not trigger an immediate last-time-buy deadline, but it does put the clock on long-term availability — qualify an alternate before the next allocation cycle tightens supply.
168 MHz Cortex-M4 with 1 MB Flash — what it delivers
The 1 MB of on-chip Flash and 192 KB of SRAM give it the memory headroom for a real-time control stack with a modest communications protocol layer — think motor drive with field-oriented control, or a multi-protocol gateway handling CAN, USB OTG, and Ethernet simultaneously. The 72 I/O lines, mapped through the 90-ball WLCSP, provide enough GPIO for parallel display interfaces or a sensor array without external port expanders.
90-WLCSP — footprint and rework considerations
This gives the smallest footprint for the 72-I/O count, but it demands a controlled SMT process: the solder balls are directly on the die pads, so the board-side pad design, solder paste volume, and reflow profile must match ST's WLCSP application note. The package is not rework-friendly — a misaligned placement typically scrapes the board. For a production line already running WLCSP, this is a known process; for a first-time user, budget for a prototype build to validate the stencil and profile.