In PCB board design, effective ESD protection can be achieved through strategic layering, proper layout, and meticulous installation. During the design phase, most adjustments involve adding or reducing components based on predictive analysis, which effectively mitigates ESD risks. Below are some recommended preventive measures:

1. Utilize multi-layer PCBs whenever possible. Compared to double-sided PCBs, multi-layer boards with dedicated ground and power planes, along with closely spaced signal lines, can significantly reduce common-mode impedance and inductive coupling, typically achieving ratios of 1/10 to 1/100 compared to double-sided PCBs. It’s advisable to place each signal layer adjacent to a power or ground layer. For densely packed PCBs with components on both sides, short interconnection lines, and ample fill areas, consider utilizing inner layer traces.

2. For double-sided PCBs, employ densely intertwined power and ground grids where power lines run closely parallel to ground lines. Maximize the number of connections between vertical and horizontal lines or fill areas. Keep the grid size on each side equal to or less than 60mm, ideally aiming for less than 13mm where feasible. Ensure compact circuitry design for each module.

3. Below connectors leading outside the chassis (vulnerable to ESD), place broad chassis ground traces or polygonal fills on all PCB layers, interconnected via vias spaced approximately 13mm apart.

4. Position mounting holes along the card edge and connect top and bottom pads directly to the chassis ground without solder resist around these holes. During PCB assembly, avoid applying solder to these pads; instead, use screws with integrated washers to ensure secure contact between the PCB and the metal chassis or shielding layer.

5. Maintain a consistent “isolation zone” between the chassis ground and circuit ground across all layers, aiming for a separation distance of 0.64mm where possible. Near mounting holes on the top and bottom layers, use 1.27mm wide traces to connect the chassis ground and circuit ground every 100mm. Adjacent to these connection points, provide pads or mounting holes for potential installation of magnetic beads or high-frequency capacitors to manage ground connections, which can be selectively cut or bridged as needed.

6. If the circuit board will not be enclosed in a metal chassis or shield, avoid applying solder resist to the top and bottom chassis ground traces. This allows these traces to function as discharge electrodes for ESD arcs.

7. Implement a ring ground around the circuit as follows:

– Surround the entire periphery with a circular ground path, excluding only the edge connectors and chassis ground.

– Ensure the ring ground width on all layers exceeds 2.5mm.

These measures collectively enhance the PCB’s resilience against ESD, ensuring robust performance in diverse operational environments.

(3) Connect the ring grounds 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, connect the ring ground to the common ground of the circuit. For unshielded double-sided circuits, connect the ring ground to the chassis ground. Avoid applying solder resist to the ring ground to enable it to function as an ESD discharge bar. Introduce at least one 0.5mm wide gap in a specific location on the ring ground (across all layers) to prevent forming a large loop. Ensure that the distance between signal wiring and the ring ground is no less than 0.5mm. In areas susceptible to direct ESD, place a ground wire near each signal wire.

(7) Typically, place series resistors and magnetic beads on the receiving end. For cable drivers prone to ESD, consider placing series resistors or magnetic beads on the driving end as well.

(8) Install a transient protector 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. Directly connect the signal and ground wires from the connector to the transient protector before connecting them to other parts of the circuit. Place a filter capacitor at the connector or within 25mm of the receiving circuit.

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

(2) Connect the signal wire and ground wire to the capacitor first, then to the receiving circuit.

(3) Ensure that the signal line is kept as short as possible.

(4) When the length of the signal wire exceeds 300mm, lay a ground wire in parallel.

(5) Ensure that the loop area between the signal line and its corresponding return path is minimized. For long signal lines, alternate the position of the signal line and ground line every few centimeters to reduce the loop area.

(6) Drive signals from the center of the network into multiple receiving circuits. Ensure that the loop area between the power supply and ground is minimized, and place a high-frequency capacitor close to each power supply pin of the integrated circuit chip.

(7) Place a high-frequency bypass capacitor within 80mm of each connector. Whenever possible, fill unused areas with ground plane, and connect the filled ground plane across all layers at intervals of 60mm. Ensure to connect to ground at two opposing ends of any large ground plane filling area (approximately greater than 25mm * 6mm).

(8) When the length of an opening on the power supply or ground plane exceeds 8mm, use a narrow trace to bridge the two sides of the opening. Ensure that reset lines, interrupt signal lines, or edge-triggered signal lines are not placed close to the edge of the PCB.

Connect mounting holes to the circuit common ground or isolate them as needed.