What are the uses of ESD testing?
When the R&D engineering team successfully develops a new electronic product, there are a lot of tests should be processed prior to the mass production. Although HBM and IEC 61000-4-2 are the more widely used standards, some brand manufacturers are asking to perform the TLP (Transmission Line Pulse) testing in recent years. Even though the test methods are different, all these test standards aim to ensure electronic products reliability. An electronic product tested by a more stringent ESD test standard before shipment can be used in a wider range of applications. Whether it is used in a humid country or in a dry, cold area where easily leads to static electricity build-up, the environmental factors will not affect consumer experiences. And it is also an effective way to increase consumer confidence and trust in such brand.
HBM (component testing) and IEC 61000-4-2 (system-level testing)
The HBM testing is used to simulate the discharge from a human body delivered to the semiconductor component. For the discharge model and waveform, please refer to the article “The Importance of ESD Protection”. Currently, most integrated circuits have passed the HBM test before shipment. Once the system is assembled, a system-level ESD testing - IEC 61000-4-2, will be carried out. The RC (resistance/capacitance) module and electrostatic discharge per IEC 61000-4-2 is 150 pF / 330 Ω, while per HBM is 100 pF / 1500 Ω. It explains that the system-level IEC 61000-4-2 standard has larger capacitance and lower discharge resistance, and the test current after calculation is approximately 5 times higher than the HBM testing. This is the reason that, even if the IC has processed the HBM testing upon leaving the factory, it still requires an additional ESD protection component (TVS) for assisting system to pass the IEC 61000-4-2 standard after assembly.
TLP (Transmission Line Pulse) Testing
The TLP, HBM and IEC 61000-4-2 are intended to simulate the ESD conditions. Comparing with the ESD simulator gun for IEC 61000-4-2 that only pass or fail is reported, the TLP testing repeatedly conducts ESD simulation from low-current to high-current conditions, and simultaneously measures the voltage and current at both ends of the test object at each discharge. The TLP measurement curve can help us to further understand the I-V characteristics and clamping voltage of TVS under ESD. The clamping voltage is the operating voltage to be measured when TVS is subjected to ESD impact. Therefore, the lower clamping voltage means the TVS is more likely to assist the device to be tested to pass the ESD testing. In addition, it allows for a further comparison of clamping voltage relationship between the IC chip and TVS. So that it can be used to presume whether the TVS is capable to successfully protect the IC chip from the ESD-related damage, and is the most indicative parameter for ESD protection component.
Advantages of using TLP testing
For a single line TVS, the clamping voltage value of TVS obtained under the corresponding ESD current can be quickly found from the TLP measurement curve. A TVS with lower clamping voltage implies better protection, and the more likely the system will comply with the IEC 61000-4-2. Therefore, the TLP measurement curve can help us to presume whether the TVS is able to meet the ESD protection requirements of the system in order to pass the IEC 61000-4-2 standard on electrostatic discharge.
TLP measurement curve of AZ5413-01F: It is observed that the clamping voltage of the TVS is about 8.5 V at 16A ESD.
As for the system product, the ESD simulator gun for IEC 61000-4-2 can quickly identify the voltage level of ESD immunity, but the TLP testing will be helpful to extract the failure point of voltage. The TLP testing can be performed on the system IC chip to measure its clamping voltage under ESD energy and it allows us to compare with the TLP measurement curve of TVS. Therefore, a TVS with lower clamping voltage will be determined based on the clamping voltage of IC chip. This may help so many R&D engineers to reduce the costs of trial-and-error and minimize the time of design correction. It can explain the reason that numerous brand manufacturers have introduced the TLP testing technique recently as the verification of ESD protection for their products.
The figure below is the TLP measurement curve comparison for Notebook USB 3.1 port with and without TVS.
The clamping voltage of 11.1V is obtained when the IC chip is exposed to 3.1A ESD energy. It means that we should choose a TVS with lower clamping voltage.
It can be seen from this measurement curve that the system is able to stay in a lower clamping voltage level under higher ESD current after adding the TVS to system’s I/O ports.
Practical cases of TLP testing
1) The specifications of ESD testing is used for the 8 kV contact discharge to the audio port of desktop. The TLP measurement curves of the three TVS components under consideration are as follows:
The real results of IEC 61000-4-2 on ESD after the installation of TVS
Above results show that a TVS with lower clamping voltage is more likely to pass the higher level of ESD test.
According to the comparison of TVS clamping voltage, it can also help us to presume the test results of IEC 61000-4-2.
2) Comparison of TLP measurement curves for Notebook HDMI port with and without TVS.
This figure also shows that, if HDMI port is equipped with TVS, the TLP curve of system will follow the TVS’s. In this way, the system is able to withstand a higher ESD current while presenting a lower camping voltage, which means a better ESD immunity and has successfully passed the ESD testing.
Analysis of TLP test results
When conducting the TLPS testing on the system, we usually find that, if the clamping voltage of the TVS is not low enough, it will cause the damage of IC and lead to test failure while the TVS has passed the test. It also shows that when we select TVS, the low clamping voltage should be the first thing to look for instead of the ESD immunity of single line TVS if we take its ESD protection into consideration. Therefore, the failure on test results of component protected by TVS (but TVS is not damaged and that shall not be our purpose of adding ESD protection components) may be avoided. Because of the advantage that TLP curve brings us, Amazing Microelectronic Corp. makes sure that you can find TLP curve among every product’s datasheet, which helps us to figure out these important information we need to know. Selecting an appropriate TVS according to its TLP measurement curve can not only prevent the costly ESD damage to the IC chip in the circuit, but also improve product reliability after mass production to minimize the failure rate in warranty period, which will greatly avoid the additional expenses of circuit design adjustment.