Basics of Electrostatic Discharge (ESD) Suppression and Testing Processes

2-1. What is CASE?

CASE is a term created by combining "Connected," "Autonomous," "Shared," and "Electricity," and is a keyword that symbolizes technological innovation in the automotive industry. These four elements work together to significantly change the way automobiles work. The current trend in the automotive industry is shifting from the conventional era of internal combustion engines (ICE) used in gasoline and diesel vehicles to smart mobility that makes full use of more advanced electronic control technologies.

With this technological innovation, automobiles have become more than just a means of transportation, but a "digital device" that processes information in real time. In particular, due to advances in autonomous driving technology and electrification, a large number of advanced electronic control units (ECUs) and integrated circuits (ICs) are installed inside vehicles, and their stable operation directly influences the safety of the entire vehicle. However, as the number of such electronic devices increases, the impact of electrostatic discharge (ESD) is becoming a more important issue.

2-2. Why is ESD Suppression Necessary?

The impact of ESD is a more direct issue for electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs) as these vehicles' driving and control systems are all controlled by electronic devices.

For example, if a high-voltage ESD is applied to an IC or ECU, there is a risk that the motor will lose control and, in the worst case, the car will become undrivable. As ESD is instantaneous, it can also cause a system malfunction or unstable operation. In addition, it can affect the memory device, which may lead to the loss of vehicle data or malfunction.

Thus, as technological innovation progresses through CASE, ESD suppression will become an essential element in ensuring the safety and reliability of automobiles. As the number of electronic devices used in vehicles increases, there is a need for measures to minimize the impact of ESD.

3-1. Main Evaluation Standards (IEC 61000-4-2 / ISO 10605)

Evaluations are carried out to accurately check the immunity and performance of components. Evaluation processes are carried out in accordance with standards such as IEC 61000-4-2 and ISO 10605, which are recognized as standardized evaluation methods. These standards are for carrying out evaluation not only at a device level for individual components but also at a system level, which is closer to the actual usage environment.

In the actual evaluation, a high voltage is applied via the contact discharge method using an ESD simulator with the capacitance and resistance shown in Table 1. Fig. 2 shows the circuit configuration of an ESD simulator with a 150 pF capacitance and a 330 Ω resistance. This method is used to check the level of voltage that a component or system can withstand as well as what failure modes can occur.

3-2. ESD Voltage Step-up Test and Repeated Application Test

The basic testing process for ESD tests is shown in Fig. 3. First, various characteristics before the test are measured as an initial measurement. Then, ESD is applied according to the specified test level of each test.
ESD voltage step-up test and repeated application test are carried out to evaluate ESD immunity. During the ESD voltage step-up test, the voltage is incrementally increased to identify the maximum voltage that a component can withstand. On the other hand, in the repeated life test, the same voltage is applied multiple times to evaluate the deterioration and durability of the component and to check the voltage level at which failures start to occur.
By combining these tests, you can check the extent to which components are affected by ESD in actual usage conditions and consider the optimum countermeasures.

3-3. Observation of Discharge Phenomena Using a Visualization Camera

The ESD visualization camera used in our test is the BV-C2950 manufactured by BlueVision Co., Ltd. Its overall specifications are shown in Table 2. Using this ESD visualization camera, the discharge phenomenon can be visualized in real time. As the camera is equipped with the function to capture near-ultraviolet rays, it can record phenomena such as discharges between terminals, which are normally invisible to the naked eye. In addition, as it can also capture discharges at low voltages, it is effective as a means of accurately grasping the location of defects and the timing of their occurrence. With the ability to accurately identify the specific location and time at which discharges occur, it can be a very useful tool for analyzing the cause of failures and improving the design.

4-1. Test Subjects

In this report, ESD tests were conducted on multi-layer ceramic capacitors (MLCCs) and multi-layer ceramic varistors (MLCVs), considering them as ESD suppression components for automotive equipment using an ESD simulator with the configuration shown in Fig. 2 and their performance was evaluated. MLCCs have conventionally been used in automotive equipment for ESD suppression, and MLCVs have been recently used in automotive interfaces such as controller area network (CAN) due to their excellent ability to ensure signal integrity (SI). Both of them are ceramic multilayer electronic components.

4-2. Changes in Characteristics of MLCCs

Fig. 4 shows a map of the allowable ESD level as a safety area from the perspective of discharge abnormalities and characteristic abnormalities (capacitance change rate and short circuit failure). The characteristics of MLCCs significantly changed when an ESD of 8 kV or more was applied. In tests at high voltages, discharges tend to occur between and inside the terminals and the immunity tends to be lower especially in small-capacitance and small-sized capacitors. In addition, it was confirmed that short circuit failures inside the capacitor and leakage current increased when ESD was applied repeatedly.

4-3. Advantages of High Immunity and No Discharge of MLCVs

Fig. 5 shows the results of comparing the suppression voltage of MLCVs. Discharges or failures did not occur up to voltages as high as 30 kV, indicating that MLCVs are very immune to ESD. This allows stable performance to be maintained even in situations affected by high voltages. In addition, the suppression voltage is kept low, which minimizes the impact on the circuit. As a result, MLCVs provide both high ESD immunity and stable suppression voltage so they are ideal for the protection of automotive electronic devices.