4 Mbit FRAM at 108 MHz — the SPI speed ceiling
The CY15B104QSN-108SXI is a 4 Mbit non-volatile FRAM from Infineon's Excelon-Ultra series, organized as 512K x 8 bits. FRAM writes are non-volatile and do not require a page-erase cycle like NOR flash. The write energy is lower, and the write endurance is effectively unlimited for field logging — no wear-leveling scheme needed at the application layer.
No special reflow profile beyond the standard JEDEC level — rework with hot air is straightforward.
ROHS3 compliant per the manufacturer's declaration.