How to prevent static electricity in PCB design

Friction caused by daily activities such as walking and dressing will generate static electrostatic voltage of different amplitude values, but its energy will not harm the human body. However, for electronic components, this static energy cannot be ignored. of.

In a dry environment, the voltage of human static electricity (ESD) easily exceeds 6~35kV. When the components on the electronic device, PCB or PCB are touched by hand, the component or equipment will suffer instantaneous static discharge, which will cause the components or equipment to receive equipment or equipment. Interference, even damage to PCB devices or components.

Static electric voltage generated by different behaviors:

Static electricity generated by the human body in daily life
way	Static voltage/Kv
	humidity10%-20%	humidity65%-90%
Walking on the carpet	35	1.5
Walking on vinyl flooring	12	0.25
Working on a workbench	6	0.1
Open the B-fired resin packaging material	7	0.6
Pick up a regular polyethylene bag	20	1.2
Sit on the gas gathering vinegar foam chair	18	1.5

How static electricity is generated

Static electricity is a kind of electrical energy. It exists on the surface of the object. It is a phenomenon produced by positive and negative charges when local imbalances occur. For example, if rubbing is called, it is a static discharge phenomenon.

The problem of static electricity has always plagued many electronic products. The electromagnetic field generated by the discharge current is severely interfered with the circuit through capacitor coupling, inductive coupling or spatial radiation coupling. Therefore, in the early stages of PCB design, we must consider static electricity. Protection issues.

There are three main reasons for static electricity:

1. Mo: In daily life, after contact with any two different materials is separated, it can generate static electricity, and the most common way to generate static electricity is to rub raw electricity.

2. Induction: For conductive materials, because electrons can flow freely on its surface, such as placing it in an electric field, because the same sex is reprimanded, the opposite sex is sucking, and positive electrons will be installed to generate static electricity;

3. Transmission: For conductive materials, because electrons can flow freely on its surface, such as contact with electrical objects, charges will be transferred to generate electrostatic electricity.

How to design anti-static electricity on PCB

The PCB layout principle generally uses the electrostatic protection device as close to the input or connector as possible. The distance between the electrostatic protection device and the protection line should be designed as short as possible.

For PCB design, it is very important to set a certain isolation distance at the edge of the static discharge edge. For rack products, the breakdown distance of the electrostatic voltage per thousand volts is about 1mm. 3~5mm insulation area can withstand 3~5kV static voltage.

1. Static Power Protection Design for Low Speed Plate

1）The wiring needs to be horizontal and vertical to minimize the signal line side by side;

2）If space permits, the thicker the wiring, the better;

3) Wiring according to the design concept of high-speed circuit;

4) Avoid processing important signal lines on PCB edges, such as clocks, reset signals, etc.;

5) The conduction ring of all PCB boards, including the power supply and ground line, should be as small as possible;

6) Single-sided or double-sided panels. If there is no power plane, a ground wire must be followed by the power supply line;

7) Try to use multi-layer wiring.

 

2. High-speed static electricity protection design

1) The wiring requires a good horizon.

2) Keep sufficient distance, such as filter, optocoupler, AC power cord and weak signal line;

3) Long-distance wiring plus low-pass filter (C, electrostatic device, RC, LC);

4) Isolation (increase shielding cover) to avoid the protected wires and unprotected wires running side by side;

5) Avoid using the same circuit as other devices to connect to the public location.

 

3. Prevent universal methods for preventing static electricity

1) Keep the ground intact, increase the leakage area of the ground, evenly spread the copper, keep the resistance of the ground unchanged, and the horizontal state of the horizontal state is stable;

2) Surrounding land design, surrounded by data cable land;

3) holes in the ground, the better, and the ground is closely connected together.

4) Install an optocoupler or transformer on the PCB, and isolation and shielding in combination with the medium can inhibit the static discharge impact;

5) You can perform a single point ground with the PCB GND with the shell to prevent voltage coupling of the voltage generated by the electrostatic discharge current on the chassis.

6) If the PCB area is allowed, and the matching channels of the whole machine system are very good, the grounding protective ring can be set around the PCB, which can be treated with naked copper, and a lot of perforated connections can be used.