PCB News - Anti-static discharge methods 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. By adjusting the PCB layout and wiring, it is possible to prevent ESD well. Use multi-layer PCBs as much as possible. Compared with double-sided PCBs, the ground plane and power plane, as well as the closely arranged signal line-ground line spacing can reduce the common mode impedance. And inductive coupling, making it reach 1/10 to 1/100 of the double-sided PCB. There are components on the top and bottom surfaces, and there are very short connecting lines.

Static electricity from the human body, the environment, and even electronic equipment can cause various damages to precision semiconductor chips, such as penetrating the thin insulating layer inside the components; destroying the gates of MOSFET and CMOS components; and the triggers in CMOS devices are locked ; Short-circuit reverse-biased PN junction; Short-circuit forward-biased PN junction; Melt the welding wire or aluminum wire inside the active device. In order to eliminate electrostatic discharge (ESD) interference and damage to electronic equipment, a variety of technical measures need to be taken to prevent it.

In the design of the PCB board, the anti-ESD design of the PCB can be realized through layering, proper layout and installation. In the PCB 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.

Use multi-layer PCBs as much as possible. Compared with double-sided PCBs, the ground plane and power plane, as well as the tightly arranged signal line-ground spacing can reduce the common mode impedance and inductive coupling, making it 1/of the double-sided PCB. 10 to 1/100. Try to put each signal layer close to a power layer or ground layer. 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.

For double-sided PCBs, tightly interwoven power and ground grids are 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. Make sure that each circuit is as compact as possible.

put all the connectors aside as much as possible

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

On all PCB layers below the connector leading to the outside of the chassis (which is easy to be directly hit by ESD), place a wide chassis ground or polygonal fill ground, and connect them together with vias at approximately 13mm distances.

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.

During PCB assembly, 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.

Between the chassis ground and circuit ground of each layer, the same "isolation zone" should be set; if possible, keep the separation distance 0.64mm. At the top and bottom layers of the card near the mounting holes, along the chassis ground every 100mm The wire connects the chassis ground and the circuit ground with a 1.27mm wide 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.

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.