header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private",false); // required for certain browsers 
header("Content-type: application/csv");
header("Content-Disposition: filename=\"filename.csv\";");
header("Content-Transfer-Encoding: binary");

Force download (CSV) file

PHP