Electronic products are everywhere in modern times. From smartphones and tablets for everyday use to precision instruments in the industrial sector, stability and reliability are of Paramount importance. Electrostatic discharge (ESD), as a key factor affecting the performance of electronic products, can lead to equipment failure, data loss and even permanent damage. Among them, air discharge and contact discharge are the two most commonly used methods in ESD testing, and there are many differences between them in the test principle, application scenario, and test effect. In-depth comparison helps to optimize ESD protection design and improve product quality.

Contact electrostatic tip and air discharge round tip

一、Comparison between air discharge and contact discharge

The main differences between air discharge and contact discharge are listed below：

The standard stipulates that contact discharge is the preferred test method, and air discharge is used in situations where contact discharge cannot be used (such as the surface coated with an insulating layer, computer keyboard gaps, etc.). For most products or equipment with metal shells or external interfaces, these two test methods are usually required by the user。

二、ESD immunity test standard IEC61000-4-2/GB-T 17626.2 test grade

GB/T 17626.2-2018(China National standard), IEC 61000-4-2:2008 + A1:2023 (International Electrotechnical Commission standard) the content of both are technically equivalent, GB/T is equivalent to the IEC standard. The voltage levels of the two test methods are shown in the table below. The higher the level, the more stringent.

三、Protection strategy

1、Contact discharge protection strategy

l Low impedance grounding design: Conductive components such as metal shells and interfaces are grounded through multiple points, and the grounding impedance must be less than 1 Ω。

l Transient current shunt: Parallel TVS diode at the interface (such as USB, HDMI) (response time < 1ns),

Add ESD protection devices (e.g. PESD, TVS array) at power input/output。

Shanghai Leiditech sorted out a variety of interface protection into the "EMC EMC community" small program, you can consult reference。

l PCB loop area: Reduce the PCB power supply and signal loop area。

l Structural design strengthening: insulation isolation of metal components: exposed metal (buttons, screws) is isolated from the internal circuit through insulation gaskets. Use conductive foam to fill the gaps in the housing to prevent ESD intrusion through the gaps。

2、Air discharge protection strategy

l Insulation and shielding design: surface insulation treatment and electromagnetic shielding。

l Reduced coupling path: gap and aperture control, common mode interference suppression. Shell gap width < 0.5mm (avoid arc penetration), or design labyrinth structure to extend the discharge path. The heat dissipation hole adopts the honeycomb structure, the aperture is < 1mm and the metal screen is added. The signal line uses a common mode choke (CMC) to suppress high-frequency radiation interference。

l Hardware and software cooperation protection: MCU program adds Watchdog (Watchdog) and status self-test, automatic reset after ESD trigger. The key data store adopts ECC verification or dual backup mechanism to prevent data tampering。

Test and verification: The pre-test uses electrostatic gun to scan the surface of the equipment and identify weak points. Shanghai Leimao has electrostatic surge test laboratory, which can provide free test and verification. If necessary, please contact EMC brother or sales staff。

Shanghai Leiditech laboratory electrostatic test equipment free test

四、Sum up：

In short, the core of contact discharge protection is "dredging", which quickly releases energy through low-impedance grounding and transient suppression devices. Air discharge protection: The core is "isolation", using shielding and insulation to block the arc path and reduce coupling interference.

Shanghai Leimo EMC brother summed up the need to combine two strategies in real life:

Metal enclosure equipment: ground + shield + interface TVS

Plastic housing equipment: anti-static coating + internal shield + common mode choke +TVS.

Leiditech is committed to becoming a leading brand in the supply of electromagnetic compatibility solutions and components, supplying ESD, TVS, TSS, GDT, MOV, MOSFET, Zener, inductors and other products. Lei MAO has an experienced R & D team, can provide personalized customized services according to customer needs, to provide customers with the best quality solutions.