in your verification you are using
$_POST['search']
but in your usage you are using
$_POST['search_pad']
that is not the problem.
The main problem is a classic rookie mistake :)
$sql = "SELECT * FROM tbl_masterlist";
$sql .= "where p0_product = '{$search_term}' ";
$sql="SELECT * FROM tbl_masterlistwhere p0_product = 'search term'";