To calculate mean time between failures (MTBF), use 1/FIT.
The reliability stress tests are conducted according to the conditions specified at JEDEC Solid State Technology Association's reliability test methods for packaged devices (JESD22), except for Group B and D tests in which DSCC's test methods, MIL-STD-883 are followed.
Reliability-based testing and the related published data does not apply to engineering samples (ES parts).
2) Expected lifetime of a Xilinx Device:
All products meet >20 year life at 85°C.
All XC E/I-grade products meet > 10 year life at 100°C(1).
All XA and XQ products meet >10 year life at 100°C, and >3 year life at 125°C.
The recommended maximum operating temperature for high-bandwidth memory is 95°C.
For longer or more accurate prediction of product life specific to your application, please contact your FAE and the Xilinx quality team.