PCB circuit board so that the adjustment of wiring can effectively prevent static electricity

Sometimes, some static electricity phenomenon occurs on the circuit board, and this phenomenon will have a certain impact on the circuit board. For example, static electricity can penetrate the thin insulating layer inside the components,2 oz copper thickness in mm damage the gate of the MOSFET and CMOS components, resulting in CMOS devices in the trigger lock, short-circuit reverse-biased PN junctions, short-circuit forward-biased PN junctions, and even melt the soldering wire or aluminum wire inside the active device and other issues. These are various damages to precision semiconductor chips caused by static electricity inside the human body, environment or electronic devices.

In order to eliminate electrostatic discharge (ESD) on electronic equipment interference and damage, we need to take a variety of technical means of prevention. In fact, engineers in the design of PCB circuit boards often through layering, proper layout wiring and mounting to achieve the anti-ESD design of the PCB. By prediction, the vast majority of design modifications can be limited to the addition or subtraction of components. By adjusting the PCB layout and wiring, can be well protected against ESD. the following is a compilation of some common preventive measures.

First, try to use multilayer boards. As opposed to the ground and power planes of a double-sided board and the tightly spaced signal lines - ground, multilayer boards can reduce common mode impedance and inductive coupling to 1/10 to 1/100 of a double-sided board. try to place each signal layer next to a power or ground layer. For high-density PCBs with components on both the top and bottom surfaces, with very short connecting wires, and many filled grounds, consider using inner layer wires.

For double-sided boards, use tightly interwoven power and ground grids. The power lines are close to the ground lines, and as many connections as possible are made between vertical and horizontal lines or infill areas. The grid size on one side should be less than or equal to 60mm, and if possible, the grid size should be less than 13mm.

Ensure that each circuit is as compact as possible.

Try to keep all connectors on one side.

If possible, bring power cables in from the center of the card and away from areas susceptible to direct ESD.

On all PCB layers below the connectors leading out of the chassis (which are susceptible to direct ESD), place wide chassis grounds or polygonal filler grounds, and then connect them together with via holes at approximately 13mm intervals.

Place mounting holes on the edges of the card, and connect the top and bottom pads around the mounting holes to the chassis ground with soldermask-free pads.

Do not apply any solder to the top or bottom pads during PCB assembly. Use screws with embedded washers to achieve tight contact between the PCB circuit board and the metal chassis/shield or bracket on the ground plane.

Provide the same "separation zone" between chassis ground and circuit ground on each layer. Keeping the separation distance at 0.64mm is relatively good.

On the top and bottom of the card, near the mounting holes, connect the chassis ground to the circuit ground with 1.27mm wide wires along the chassis ground at 100mm intervals. Adjacent to these connections, pads or mounting holes for mounting are placed between chassis ground and circuit ground. These ground connections can be scored with a razor blade to maintain an open circuit, or jumpered with a bead/high-frequency capacitor.

Solder resist should not be applied to the top and bottom chassis grounds of the circuit board if the board is not placed in a metal chassis or shielded device so that they can act as discharge electrodes for ESD arcs. To provide a ring ground around the circuit in the following manner:

(1) Place a ring ground path around the entire perimeter except for the edge connectors as well as the chassis ground.

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

(3) Connect the ringlands with over-holes every 13 mm.

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

(5) For double-sided panels mounted in a metal chassis or shielded unit, ring ground should be connected to the circuit common ground.plated through hole vs via For unshielded double-sided circuits, connect the ring ground to chassis ground. The ring ground should not be coated with solder resist so that the ring ground can act as an ESD discharge bar. Place at least a 0.5mm wide gap somewhere on the ring ground (all layers) to avoid forming a large loop. Signal cabling should not be less than 0.5mm away from the ring ground.