You should use leftBarBttonItem
for custom back button
UIImage *temp = [[UIImage imageNamed:@"button_back.png"] imageWithRenderingMode: UIImageRenderingModeAlwaysOriginal];
UIBarButtonItem *backButton = [[UIBarButtonItem alloc] initWithImage:temp style:UIBarButtonItemStyleBordered target:self action:@selector(action)];
self navigationItem.leftBarButtonItem = backButton;