If you need to keep a sql server backup independent of the sequence of conventional backups it can be acheived with copy only backups. A copy-only backup will not impact the overall backup and restore procedures for the database and is created independently of the regular scheduled conventional backups.
A copy-only full backup is not supported within SQL Server Management Studio. The script below should be used:-
BACKUP DATABASE database_name
TO DISK = 'F:\oneoffbackups\database_name_date_time.bak'