Apple logic board package 820-3115 revision B in a small 152 KB ZIP archive. The 820-xxxx format is Apple's own board numbering, with the trailing letter indicating revision, so a revision B file should be matched to a revision B board. No Mac model or content list appears in the name; at this size it is most likely a boardview. Open the extracted layout in a boardview viewer to locate parts, trace rails and nets, and probe test points when hunting shorts or missing voltages.
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 @ITHINKHS. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.
Built-in OS tools7-Zip