Improvement scheme of electronic factory plug-in. According to the relevant public information, the foolproof measures to prevent reverse insertion should be controlled by a fixture, because the length of the positive and negative pins of led is different, so this characteristic should be used to control. The PCB is placed on a fixture with holes, and the drilling depth is the key. The drilling depth of the positive and negative pins is slightly larger than the exposed length of the pins after passing through the PCB, and the positive pin is longer than the negative pin. When the LED is reversely connected, the long positive pin is pushed up by the shallow negative pin.