How to achieve anti-ESD design of PCB
2023-12-20
In the design of PCB boards, the ESD-resistant design of PCBs can be achieved through layering, proper layout and mounting. During the design process, predictions can limit the vast majority of design changes to the addition or removal of components. By adjusting the PCB layout and routing, ESD can be well protected.
Static PCB reading electricity from the human body, the environment, and even the inside of the electrical PCB copy board will cause various damage to the precision semiconductor chip, such as penetrating the thin insulation layer inside the component, damaging the gate of the MOSFET and CMOS components, locking the flip-flop in the CMOS PCB copy board, short-circuit reverse biased PN junction, short-circuit positive PCB copy board biased PN junction, PCB copy board melting the solder wire or aluminum wire of the PCB copy board in the active device. In order to eliminate the interference and damage of electrostatic discharge (ESD) to electronic equipment, a variety of technical means are required to prevent it.
In the design of the PCB, the anti-ESD design of the PCB can be achieved through layered and appropriate layout, PCB copying, layout and installation. During the design process, predictions can limit the vast majority of design changes to the addition or removal of components. By adjusting the PCB layout and wiring, it is possible to prevent PCB copy board ESD. Here are some common precautions.
Whenever possible, multilayer PCBs are used, with ground and power planes and tightly packed signal-ground spacing reducing common-mode impedance and inductive coupling to 1/100 of a double-sided PCB compared to double-sided PCBs. Try to keep each signal layer close to a power or ground plane. For high-density PCBs that have components on both the top and bottom surfaces, have very short connection lines, and have many filled grounds, consider using inner lines. For double-sided PCBs, tightly intertwined power and ground grids are used. The power cord is close to the ground wire, and between the vertical and horizontal wires or the fill area, as much as possible. The size of the grid PCB on one side should be less than or equal to 60mm, and if possible, the grid size should be less than 13mm.
Make sure that each circuit PCB copy board is as compact as possible.
Set all connectors aside as much as possible.
If possible, introduce the power PCB copy line from the center of the card and away from areas that are susceptible to direct ESD impacts.
Place wide chassis or polygonal fills on all PCB layers below the connectors that lead to the outside of the chassis (which are prone to PCB copy boards being directly hit by ESD) and connect them together with vias at intervals of approximately 13mm.
Place the PCB copy board on the edge of the card and place the mounting holes, and connect the top and bottom pads of the PCB copy board without solder mask to the chassis around the mounting holes.
When assembling a PCB, do not apply any solder to the top or bottom pads of the PCB. Use screws with built-in PCB washers to achieve close contact between the PCB and the metal chassis, PCB/shield, or bracket on the ground plane.
The same "isolation zone" is set between the chassis ground and circuit ground on each level, and if possible, the separation distance is 0.64mm.
At the top and bottom layers of the card near the mounting holes of the PCB, connect the chassis ground and circuit ground together with 1.27mm wide wires along the chassis ground every 100mm. Adjacent to these connection points, pads or mounting holes are placed between the chassis floor and the circuit floor PCB copy board for mounting. These ground connections can be cut open with blades to keep an open circuit, or patched with beads/high-frequency capacitors.
If the board will not fit into a metal chassis or PCB shielding device, solder masks should not be applied to the ground wires of the top and bottom chassis of the board, so that they can act as discharge electrodes for the ESD arc.
To set up a ring around the circuit in the following PCB row arrangement:
(1) In addition to the edge connecting the PCB reader and the chassis floor, put a circular ground path around the entire perimeter.
(2) Make sure that the width of the annular ground of all layers is greater than 2.5mm.
(3) Ring the connection every 13 mm with vias.
(4) Connect the ring ground with the common ground of the multilayer PCB copy board circuit.
(5) For double-sided PCB boards installed in metal chassis or shielding devices, the ring ground should be connected to the circuit in a common way. Unshielded double-sided circuits should be connected to the chassis ground in a ring shape that cannot be coated with solder mask so that the ring can act as a discharge rod for the ESD, and a gap of at least 0.5mm wide should be placed somewhere on the ring ground (all layers) to avoid a large loop on the PCB copy board. The distance between the signal wiring and the ring ground should not be less than 0.5mm.
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