Considering the anti-static characteristics of different shell materials in the design stage is the key to solving ESD problems, Lei MAO EMC brother will detail the anti-static design skills for metal structural equipment, plastic structural equipment and other special cases.

First, anti-static design of metal structure equipment

Metal structure equipment is the preferred material in many industrial applications because of its good electrical conductivity. However, this property also makes it vulnerable to electrostatic discharge. In order to effectively deal with this problem, metal structure equipment can be divided into two categories according to whether it is grounded:

A type of equipment: metal structure equipment, metal shell ground

For this type of equipment, the core principle of solving ESD problems is to quickly discharge electrostatic current. Discharge points of such equipment: housing, connector housing, indicator light, reset button, dip switch, power switch, etc.;

Specific measures include:

Determine the electrostatic discharge path: Lay out the device cover and draw a straight line from the discharge point to the ground point to determine the electrostatic discharge path.

Check path patency: Ensure that no structural holes cause the electrostatic field to radiate into the device, and that the discharge point and ground point are on the same structural part.

Dealing with internal cable interference: Change the cable routing mode away from the discharge path or slot; A magnetic loop is added to the signal line to cut off the common mode current induced by static electricity.

Metallization of ground terminal: In order to ensure a large area of lap, metallization is performed around the screw fall.

Connector protection: Ensure that the metal housing of the connector is in good contact with the device housing to avoid sensitive circuits near the interface connector.

Port protection paradigm

Panel, display, keyboard ESD troubleshooting

² The best and most effective way is to paste an insulating film on the surface of the keyboard and display screen so that static electricity cannot be discharged in these parts.

² Add magnetic ring on the control line for electrostatic pulse suppression.

² For screens with shielded metal mesh, the metal mesh should be well overlapped with the structural parts.

Type II equipment: metal structure equipment, the shell is not connected to the ground

Such equipment, such as MP3 players, although the housing is not grounded, but still need to take appropriate measures to prevent ESD damage. The main discharge points of such devices: shell, connector shell, indicator light, reset button, dip switch, power switch, etc., so these places should be dealt with when electrostatic problems occur.

Discharge to the device enclosure. In the case shown in the following figure, there is no electrical connection between the circuit in the device and the metal enclosure, and the cable in the device is grounded at the far end.

Treatment measures: make it connected to the external grounded line and the shell, and use the twisted pair to transmit the signal.

Discharge to the equipment shell, the circuit in the equipment and the metal shell are electrically connected, and the circuit cable in the equipment is grounded at the far end;

Remove the connection between the circuit and the enclosure, and connect it to the outer grounded line and the enclosure.

Remove the connection between the circuit and the housing, and use the twisted pair to transmit the signal.

Second, the anti-static design of plastic structure insulation shell equipment

Plastics are widely used in consumer electronics as non-conductive materials, but their insulating properties make ESD protection more challenging. For such devices, the following points are particularly important:

1. Insulation enclosures

The electrostatic test is mainly for the insulation shell (air discharge), metal connector shell (direct discharge) and plastic connector shell (air discharge).

The solution is as follows:

Space isolation: Keep a sufficient distance between the board and the insulation housing, especially the PCB board near the holes must be far away from the structural holes.

l Surface film: Attach an insulating film to the surface of the keyboard and display screen to prevent electrostatic discharge.

l Control line with magnetic ring: inhibit electrostatic pulse.

l Shielded mesh bonding: For screens with shielded metal mesh, ensure that the metal mesh is well bonded to the structural parts.

2. Contact discharge of metal connector shell

When the metal shell is not the return point of the signal line (such as the RS-232 serial port), the following solution is recommended:

l The board divides the PGND and GND areas.

l Connector The metal shell is connected to the PGND and connects to the ground through the ground cable. There is no connection between PGND and GND.

l Each signal line suppresses the static pulse of PGND connected TVS tube.

Third, anti-static design under special circumstances

In addition to the above categories, there are some special scenarios that require special attention:

l Internal conductive components extend out of the housing

If the system has internal conductive parts sticking out of the housing, these parts should be properly shielded and ESD coupling should be reduced with good grounding.

l PCB board level antistatic design

PCB design process can be layered, reasonable layout and wiring, and correct installation to achieve ESD resistance. For example, a series resistance at a high input impedance port enhances protection.

l Electrostatic shielding and magnetic shielding

Sensitive devices are protected from ESD by electrostatic shielding. Electrostatic shielding usually uses a well-conductive metal sheet to block the transmission of electric field force lines. It is worth noting that the distributed capacitor C02 can be formed even if it is not grounded after shielding, so as to play a role in voltage division and reduce interference voltage.

Four, ESD device key parameter requirements

1) Silicon-based materials:

2) Polymer materials:

3) Ordinary pressure sensitive:

Five. Leiditech Electronic professional lightning anti-static:

In short, for the anti-static design of different shell materials, it is necessary to comprehensively consider the characteristics of the equipment and its actual application environment. Whether it is metal or plastic material, its core is to achieve rapid discharge of electrostatic current through reasonable structural design and material selection.

In the specific implementation process, a variety of protection means should be flexibly used to meet the needs of different scenarios. Leiditech has been deeply engaged in the field of EMC electrostatic protection for many years, and has written more than 200 pages of "Electromagnetic compatibility 100 Questions 100 Answers" and interface anti-static solution dictionary. Welcome to LeidITech emc brother for requests.

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.