How to enhance the anti-static ESD function of PCB copy board
In the design of PCB board, the anti-ESD design of PCB can be achieved through layering, proper layout, wiring and installation. In the design process, most design modifications can be limited to adding or reducing components through prediction. By adjusting the PCB layout and wiring, ESD can be well prevented.
Static electricity from the human body, environment and even inside the electronic equipment can cause various damages to precision semiconductor chips, such as penetrating the thin insulation layer inside the components; damaging the gate of MOSFET and CMOS components; locking the trigger in the CMOS device; short-circuiting the reverse biased PN junction; short-circuiting the forward biased PN junction; melting the welding wire or aluminum wire in the active device. In order to eliminate the interference and damage of electrostatic discharge (ESD) to electronic equipment, a variety of technical means need to be taken to prevent it.
In the design of PCB board, the anti-ESD design of PCB can be achieved through layering, proper layout, wiring and installation. In the design process, most design modifications can be limited to adding or reducing components through prediction. By adjusting the PCB layout, ESD can be well prevented. Here are some common preventive measures.
Use multi-layer PCBs as much as possible. Ground planes and power planes, as well as closely spaced signal lines and ground lines can reduce common-mode impedance and inductive coupling to 1/10 to 1/100 of that of double-sided PCBs. Try to keep each signal layer close to a power or ground layer. For high-density PCBs with components on both the top and bottom surfaces, very short connecting lines, and many fills, consider using inner layer lines. For double-sided PCBs, use tightly interwoven power and ground grids. Keep power lines close to ground lines, and connect as many as possible between vertical and horizontal lines or fill areas. The grid size on one side is less than or equal to 60mm, and if possible, the grid size should be less than 13mm.
Make sure each circuit is as compact as possible.
Put all connectors on one side as much as possible.
If possible, route power PCB traces from the center of the card and away from areas that are directly exposed to ESD.
On all PCB layers below connectors that lead out of the chassis (where they are directly exposed to ESD), place wide chassis ground or polygon-filled ground and connect them together with vias every approximately 13mm.
Place mounting holes on the edge of the card and connect them to the chassis ground with top and bottom pads without solder mask around the mounting holes.
When assembling the PCB, do not apply any solder to the top or bottom pads. Use screws with built-in PCB washers to achieve close contact between the PCB and the metal chassis/shield or bracket on the ground plane.
Set the same “isolation zone” between the chassis ground and circuit ground on each layer; if possible, keep the spacing distance at 0.64mm.
On the top and bottom layers of the card, near the PCB mounting holes, connect the chassis ground and circuit ground with 1.27mm wide wires every 100mm along the chassis ground line. Adjacent to these connection points, place mounting pads or mounting holes between the chassis ground and circuit ground PCB. These ground connections can be cut with a blade to keep them open, or jumpered with beads/high-frequency capacitors.
If the board will not be placed in a metal chassis or PCB shield, do not apply solder mask to the top and bottom chassis ground lines of the board so that they can act as discharge electrodes for ESD arcs.
To set up a ring ground around the circuit in the following way:
(1) Place a ring ground path around the entire periphery, except for the edge connection to the PCB board and chassis ground.
(2) Make sure the width of the ring ground is greater than 2.5mm on all layers.
(3) Connect the ring ground with vias every 13mm.
(4) Connect the ring ground to the common ground of the multi-layer PCB copy board circuit.
(5) For double-sided PCB copy boards installed in metal chassis or shielding devices, the ring ground should be connected to the circuit common ground. For unshielded double-sided circuits, the ring ground should be connected to the chassis ground. No solder resist should be applied to the ring ground so that the ring ground can act as an ESD discharge rod. At least a 0.5mm wide gap should be placed somewhere on the ring ground (all layers) to avoid the PCB copy board from forming a large loop. The distance between the signal wiring and the ring ground cannot be less than 0.5mm.