RAR archive named L640 U20, a companion to other L640 files, but only 228 bytes in size, which is too small to hold a usable firmware image or document. It is likely empty, damaged or contains only a tiny text file or placeholder. U20 is probably a component designator on the board, though the name does not say so. Test the archive and check its contents before relying on it, and look for a complete source for the chip you need.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @vinafix_bios. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.
7-ZipWinRARThe Unarchiver (macOS)