Почему не срабатывает “success” в ajax запросе?

вот код:

JS:

 function regUtmInDB(){
  var done = "";
  var utm_name = $("#utm_name").val();
  var manager = $("#manager").val();
  var site = $("#site").val();
  var prod_id = $("#prod_id").val();
  var age_min = $("#age_min").val();
  var age_max = $("#age_max").val();
  var gender = $("#gender").val();
  var subids = $('.subid');
  //    var s = Array;
  //    for(i=0;i<subids.length;i++){
  //            if($("#subid_"+i+"_value").val()!=""){
  //                s[i] = $("#subid_"+i+"_value").val();
  //            }  
  //        }
  $.ajax({
               url: "cart/subidReg.php",
               type: "POST",
               data: ({
                    utm_name : utm_name,
                    manager : manager,
                    site : site,
                    prod_id : prod_id,
                    age_min : age_min,
                    age_max : age_max,
                    gender : gender,
                    subids : subids
                }), 
               processData: false,
               success: function(data){
                  done = data;
                },
            });
   return done;
  }

PHP:

<?php 
if (isset($_POST["utm_name"])){
$utm_name = $_POST["utm_name"];
$manager = $_POST["manager"];
$site = $_POST["site"];
$prod_id = $_POST["prod_id"];
$age_min = $_POST["age_min"];
$age_max = $_POST["age_max"];
$gender = $_POST["gender"];
$subids = $_POST["subids"];
if($utm_name!=""){echo true;}
else{echo false;}
}else{
echo true;
}
?>