SQL Server credentials - Maximum Password size
Passwords are case-sensitive. Passwords should always be at least 8
  characters long, and cannot exceed 128 characters. Passwords can
  include a-z, A-Z, 0-9, and most non-alphanumeric characters. Passwords
  cannot contain single quotes, or the login_name.


https://msdn.microsoft.com/en-us/library/ms189751.aspx