Hi, we are using Cyclone II EP2C50 series FPGAs for one of the control product. We are using CRAM CRC check inbuilt feature for any SEU, It is observed in recent years the CRC errors got increased.

This FPGA is used in module with proper grounded metal casing and controlled environment w.r.t atmosphere (there almost four layers metallic enclosures from sun expose). Really doubt can cosmic rays ...