PCB resistance to transient conductivity and PCB resistance to electromagnetic radiation

The main purpose of this test is to verify the resistance to electrostatic discharge (ESD) caused by the proximity or contact of an object or person or device. An object or a person can accumulate an electrostatic charge inside of a voltage higher than 15kv. Experience shows that many unexplained failures and damages are likely caused by ESD. By discharging from the ESD simulator to the surface of and near the EUT, the test instrument (EUT) captures ESD activity. The severity level of discharge is clearly defined in product standards and EMC test plans prepared by the manufacturer. EUT checks for functional failures or interference in all of its operational modes. Pass/fail criteria must be defined in the EMC test plan and determined by the manufacturer of the product.

PCB transient conductivity resistance

The main purpose of this test is to verify the resistance of the EUT to transient and short-duration shocks with rapid rising time that may be generated by inductive loads or contactors. The rapid rise time and repetitive nature of this test pulse results in these spikes easily penetrating EUT circuits and potentially interfering with EUT operations. Transients acting directly on the main power supply and the permittivity of the signal line. In other PCB immunity tests, the EUT should be monitored on a pass/fail basis using a general operation configuration.


Resistance of PCB to electromagnetic radiation

The main purpose of this test is to verify the product’s PCB anti-interference capability against radios, transceivers, mobile GSM/AMPS phones, and a variety of electromagnetic fields generated from industrial electromagnetic sources. If the system is not shielded, electromagnetic radiation can be coupled to the interface cable and enter the circuit through the conduction path; Or it can be directly coupled to the wiring of a printed circuit. When the amplitude of the rf electromagnetic field is large enough, the induced voltage and demodulated carrier can affect the normal operation of the device.

PCB radiation resistance Test run This test run is usually the longest and most difficult, requiring very expensive equipment and considerable experience. In contrast to other PCB immunity tests, success/failure criteria defined by the manufacturer and a written test plan must be sent to the test room. When feeding EUT into the radiation field, the EUT must be set in normal operation and the most sensitive mode.

Normal operation must be established in the test room when EUT is exposed to graded interference fields whose frequencies exceed the required 80MHz to 1GHz frequency range. Some PCB anti-interference standards start at 27MHz. Severity level this standard typically requires PCB resistance levels of 1V/m, 3V/m, or 10V/m. However, device specifications may have their own requirements for specific “problem (interference) frequencies”. The appropriate PCB radiation resistance level of the product is of interest to the manufacturer.

Unified field requirements The new PCB interference resistance 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 realized in an anechoic room with tiles arranged with ferrite absorbers to block reflection and resonance in order to establish a unified test site indoors. This overcomes the sudden and frequent non-repeatable test errors caused by reflection and field gradients in traditional unlined rooms. (A semi-anechoic room is also an ideal environment for measuring radiation emission in an indoor abnormal environment that requires accuracy).

Construction of semi-anechoic rooms RF absorbers shall be arranged on the walls and ceilings of semi-anechoic rooms. The mechanics and RF design specifications should accommodate the heavy ferrite tiles lining the roof of the room. Ferrite bricks sit on dielectric material and are attached to the top of the room. In an unlined room, reflections from the metal surface will cause resonance and standing waves, which create peaks and troughs in the strength of the test space. The field gradient in a typical unlined room can be 20 to 40dB, and this will cause the test sample to appear to fail suddenly in a very low field. The resonance of the room results in very low test repeatability and a high rate of “overtesting”. (This may lead to over-design of the product.) The new PCB anti-interference standard IEC1000-4-3, which requires the same field requirements, has remedied these serious deficiencies.

The hardware and software required to generate the test site required a high-power broadband RF amplifier to drive the broadband transmitting antenna in the frequency range of more than 26MHz to 2GHz, which was 3 meters away from the device being tested. Fully automated testing and calibration under software control provides 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 synchronization of monitoring and stimulation of EUT functionality. Interactive features are required in actual testing to enable real-time changes in EMC testing software and EUT parameters. This user access feature allows all data to be recorded quickly for effective evaluation and partitioning of EUT EMC performance.

Pyramidal absorbers Traditional pyramidal (conical) absorbers are effective, however the sheer size of the pyramid makes it impossible to test small usable Spaces in a room. For lower frequencies of 80MHz, the length of the pyramid absorber should be reduced to 100cm, and to operate at lower frequencies of 26MHz, the length of the pyramid absorber should be greater than 2m. Pyramid absorbers also have disadvantages. They are fragile, easily damaged by collision, and flammable. It is also not practical to use these absorbers on the floor of the room. Because of the heating of the pyramid absorber, a field strength greater than 200V/m over a period of time will pose a high risk of fire.

Ferrite tile absorber

Ferrite tiles are spatially efficient, however 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 well at low frequencies, but become relatively inefficient at frequencies above 1GHz. Ferrite tiles are very dense (100mm×100mm×6mm thick) and can withstand field intensities in excess of 1000V/m without risk of fire.

Difficulties in PCB radiation resistance testing Because the auxiliary equipment used to operate the EUT provides stimulus signals to monitor its own performance, it must itself be PCB-resistant to this sensitive field, which is an inherent difficulty in running a radiation sensitivity test. This often leads to difficulties, especially when auxiliary equipment is complex and requires many cables and interfaces to the EUT that are perforated through the shielded test room. All cables running through the test room must be shielded and/or filtered so that the test field is shielded from them to avoid reducing the shielding performance of the test room. Compromises in the shielding performance of the test room will result in inadvertent leakage of the test site into the surrounding environment, which may cause interference to users of the spectrum. It is not always feasible to use RF filters for data or signal lines, such as when there is a lot of data or when high-speed data links are used.