PCB immunity standard

The purpose of this test is primarily to verify the resistance to electrostatic discharge (ESD) caused by the proximity or contact of an object or person or device. The internal charge of an object or person can accumulate an electrostatic charge that reaches a voltage higher than 15 kV. Experience has shown that many unexplained failures and damages are likely to be caused by ESD.

  The instrumentation (EUT) is used to obtain ESD activity by discharging from the ESD simulator to the surface of the EUT and near the EUT. The severity of the discharge is clearly defined in the product standards and EMC test plans prepared by the manufacturer. The EUT checks for malfunctions or disturbances in all of its operating modes. The pass/fail criteria must be defined in the EMC test plan and determined by the manufacturer of the product.

  PCB resistance to transient conductivity

  The purpose of this test is primarily to verify the EUT's resistance to transient short duration shocks that may be caused by inductive loads or contactors with fast rise times. The fast rise time and repetitive nature of such test pulses cause these spikes to easily penetrate the EUT's circuitry and may interfere with the operation of the EUT. Transients directly affect the permittivity of the total power and signal lines.

  In other PCB immunity tests, the EUT should be monitored according to pass/fail criteria using a general operational configuration.

  PCB anti-electromagnetic field radiation

  The purpose of this test is to verify the product's immunity to radios, radios, mobile GSM/AMPS phones, and various PCB electromagnetic fields from industrial electromagnetic sources. If the system is not shielded, electromagnetic field radiation can be coupled to the interface cable and enter the circuit through the conductive path; or it can be directly coupled to the wiring of the printed circuit.

  When the amplitude of the RF electromagnetic field is sufficiently large, the induced voltage and the demodulated carrier can affect the normal operation of the device.

  PCB anti-radiation test operation

  The operation of this test is usually the longest and most difficult, requiring very expensive instruments and considerable experience. Compared to other PCB immunity tests, the manufacturer's defined success/failure criteria and written test plans must be sent to the test room. When the EUT is sent to the radiation field, the EUT must be placed in normal operation and the most sensitive mode.

  Normal operation must be established in the test room when the EUT is exposed to a graded interference field that exceeds the required frequency range of 80 MHz to 1 GHz. Some PCB immunity standards start at 27MHz.

  Severity rating

  This standard typically requires 1V/m, 3V/m or 10V/m for PCB immunity levels. However, the specifications of the device may have their own requirements on specific "problem (interference) frequencies". It is the manufacturer's interest to determine how well the PCB's radiation resistance level is appropriate.

  Unified site requirements

  The new PCB immunity standard EN50082-1:1997 refers to IEC/EN61000-4-3. IEC/EN61000-4-3 requires a unified test environment based on test samples. The test environment was implemented in a watt-free, anechoic room consisting of a ferrite absorber that was used to block reflections and resonances to create a uniform test site indoors. This overcomes the sudden and often non-repeatable test errors caused by reflections and field gradients in conventional unlined rooms. (The semi-anechoic room is also an ideal environment for measuring radiated emissions that require accurate indoor abnormal conditions).

  Construction of a semi-anechoic room An RF absorber should be arranged on the walls and ceiling of a semi-anechoic room. Mechanical and RF design specifications should accommodate heavy ferrite bricks that are placed on the roof of the room. The ferrite bricks are placed on the dielectric material and attached to the top surface of the room. In a room without a lining, the reflection of the metal surface will cause resonance and standing waves, which will create peaks and troughs in the strength of the test space. The field gradient can be as much as 20 to 40 dB in a typical unlined room, and this will result in a sudden failure of the test sample in a very low field. The resonance of the room results in a very low test repeatability and a high probability of "over testing". (This may cause the product to be overdesigned.) The new field-required PCB anti-interference standard IEC1000-4-3 compensates for these serious defects.

  Generate hardware and software requirements for the test site

  High-power wideband RF amplifiers are used to drive wideband transmit antennas with frequency ranges in excess of 26MHz to 2GHz, which is 3 meters away from the equipment being tested. Fully automated testing and calibration under software control provides the best possible operation, providing greater flexibility for testing and full control of all key parameters such as scan rate, frequency pause time, modulation and field strength. Software hooks allow for synchronization of monitoring and stimulation of the functionality of the EUT. Interactive functionality is required in actual testing to enable real-time changes to EMC test software and EUT parameters. This user access feature allows for fast recording of all data in order to effectively evaluate and classify the EMC performance of the EUT.

  Pyramid Absorber The traditional pyramid (cone) absorber is effective, but the size of the pyramid makes it impossible to test small available space in a room. For lower frequencies of 80 MHz, the length of the pyramid absorber should be 100 cm, and to operate at a lower 26 MHz frequency, the length of the pyramid absorber should exceed 2 m. Pyramid absorbers also have disadvantages, they are fragile, easily destroyed by collisions, and are flammable. It is also impractical to use these absorbers on the floor of a room. Because of the heat of the pyramid absorber, a field strength greater than 200 V/m will continue to exceed a certain period of time and will pose a high risk of fire.

  Ferrite tile absorber

  Ferrite tiles are space efficient, yet they add significant weight to the roof, walls and doors of the room, so the mechanical structure of the room becomes very important. They work effectively at low frequencies, but when the frequency is above 1 GHz, their operation becomes relatively inefficient. The ferrite tile is very dense (100mm x 100mm x 6mm thick) and can withstand field strengths in excess of 1000V/m without the risk of fire.

  Difficulties in PCB radiation resistance testing

  Since the auxiliary device used to operate the EUT provides a stimulus signal to monitor its own performance, such that it must itself be anti-jamming to the sensitive field, this is an inherent difficulty in running radiation sensitivity testing. This often causes a lot of difficulties, especially in the case of auxiliary equipment, which requires a lot of cables and interfaces that are connected to the EUT through the perforated test room. All cables that pass through the test room must be shielded and/or filtered to shield the test field from them, thus avoiding a reduction in the shielding performance of the test room. A compromise on the shielding performance of the test room will cause the test site to inadvertently leak into the surrounding environment, which may interfere with the use of the spectrum. RF filters that use data or signal lines are not always feasible, such as when there is a lot of data or when a high-speed data link is used.