PCB Technical - Summarize the anti-ESD measures in PCB design

In the design of the PCB board, the anti-ESD design of the PCB can be realized through layering, appropriate layout and installation. In the design process, the vast majority of design modifications can be limited to the addition or reduction of components through prediction. By adjusting the PCB layout and routing, ESD can be well prevented. The following are some common precautions.

1. Use multilayer PCBs as much as possible

Compared with the double-sided PCB, the ground plane and the power plane, as well as the closely arranged signal line-ground spacing can reduce the common mode impedance and inductive coupling, making it reach 1/10 to 1/100 of the double-sided PCB. Try to put each signal layer close to a power layer or ground layer as much as possible. For high-density PCBs with components on the top and bottom surfaces, short connection lines, and many fills, you can consider using inner layer lines.

2. For double-sided PCBs, tightly interwoven power and ground grids should be used.

The power line is close to the ground line, and as many connections as possible between the vertical and horizontal lines or the filled area. The grid size on one side is less than or equal to 60mm. If possible, the grid size should be less than 13mm.

3. Ensure that each circuit is as compact as possible.

4. Put all the connectors aside as much as possible.

5. Set the same "isolation zone" between the chassis ground and the circuit ground on each layer; if possible, keep the separation distance 0.64mm.

6. When assembling the PCB, do not apply any solder on the top or bottom pads.

Use screws with built-in washers to achieve close contact between the PCB and the metal chassis/shielding layer or the support on the ground plane.

7. If possible, introduce the power cord from the center of the card and keep it away from areas that are directly affected by ESD.

8. On all PCB layers below the connector that leads to the outside of the chassis (which is easily hit by ESD), place a wide chassis ground or polygonal filling ground, and connect them with vias at intervals of about 13mm. Together.

9. Place mounting holes on the edge of the card, and connect the top and bottom pads with no solder resist around the mounting holes to the chassis ground.

10. On the top and bottom layers of the card near the mounting holes, connect the chassis ground and the circuit ground with a 1.27mm wide wire every 100mm along the chassis ground wire. Adjacent to these connection points, place pads or mounting holes for mounting between the chassis ground and the circuit ground. These ground connections can be cut with a blade to keep the circuit open, or jumper with magnetic beads/high-frequency capacitors.

11. If the circuit board will not be placed in a metal chassis or shielding device, solder resist should not be applied to the top and bottom chassis ground wires of the circuit board, so that they can be used as discharge electrodes for ESD arcs.

12 To set a ring ground around the circuit in the following way:

(1) In addition to the edge connector and the chassis ground, a circular ground path is placed around the entire periphery.

(2) Ensure that the annular ground width of all layers is greater than 2.5mm.

(3) Connect annularly with via holes every 13mm.

(4) Connect the ring ground to the common ground of the multilayer circuit.

(5) For double panels installed in metal cases or shielding devices, the ring ground should be connected to the common ground of the circuit. For unshielded double-sided circuits, the ring ground should be connected to the chassis ground. Solder resist should not be applied to the ring ground, so that the ring ground can act as an ESD discharge bar. Place at least one at a certain position on the ring ground (all layers) 0.5mm wide gap, so you can avoid forming a large loop. The distance between the signal wiring and the ring ground should not be less than 0.5mm.

13. In the area that can be directly hit by ESD, a ground wire must be laid near each signal line.

14. The I/O circuit should be as close as possible to the corresponding connector.

15. Circuits that are susceptible to ESD should be placed near the center of the circuit so that other circuits can provide them with a certain shielding effect.

16. A transient protector is usually placed at the receiving end. Use a short and thick wire (length less than 5 times the width, preferably less than 3 times the width) to connect to the chassis ground. The signal wire and ground wire from the connector should be directly connected to the transient protector before being connected to other parts of the circuit.

17. Generally, series resistors and magnetic beads are placed on the receiving end. For those cable drivers that are easily hit by ESD, you can also consider placing series resistors or magnetic beads on the drive end.

18 Place a filter capacitor at the connector or within 25mm from the receiving circuit.

(1) Use a short and thick wire to connect to the chassis ground or the receiving circuit ground (the length is less than 5 times the width, preferably less than 3 times the width).

(2) The PCB signal line and ground line are connected to the capacitor first and then to the receiving circuit.

18. Make sure that the PCB signal line is as short as possible.

19. When the length of the signal wire is greater than 300mm, a ground wire must be laid in parallel.

20. Ensure that the loop area between the PCB signal line and the corresponding loop is as small as possible. For long signal lines, the positions of PCB signal lines and ground lines must be exchanged every few centimeters to reduce the loop area.

21. Drive signals from the center of the network into multiple receiving PCB circuits.

22. If possible, fill the unused area with land, and connect the filling grounds of all layers at a distance of 60mm.