form-seriallize-files.js

(function($) {
	$.fn.serializeFiles = function() {
		var form = $(this);
		var formData = new FormData();
		var formParams = form.serializeArray();
		$.each(form.find('input[type="file"]'), function(i, tag) {
			$.each($(tag)[0].files, function(i, file) {
				formData.append(tag.name, file);
			});
		});
	    $.each(formParams, function(i, val) {
	      formData.append(val.name, val.value);
	    });
	    return formData;
	};
})(jQuery);

//exemplo:
//apiPOSTD('banner/salvar', $('#formPrincipal').serializeFiles(), apiCallback);