In PCB design, the anti ESD design of PCB can be realized by layering, proper layout, routing and installation. In the design process, the majority of the design changes can be limited to components only through prediction. By adjusting the layout and wiring of PCB, ESD can be well protected.
From human, environment and even electronic equipment for electrostatic semiconductor chip precision will cause various injuries, such as through the internal components of thin insulating layer; a gate MOSFET lesion and CMOS components in the CMOS device; trigger lock; short PN junction reverse biased p-n junction is short; the bias; melting active devices in welding wire or wire. In order to eliminate the interference and damage of electrostatic discharge (ESD) to electronic equipment, a variety of technical measures should be taken to prevent it.
In the design of the PCB board, the anti ESD design of PCB can be realized through layering, proper layout, routing and installation. In the design process, the majority of the design changes can be limited to components only through prediction. By adjusting the layout and wiring of PCB, ESD can be well protected. Here are some common precautions.
The use of multilayer PCB as much as possible, compared with double PCB, ground plane and power plane, and closely spaced signal earth line spacing can reduce common mode impedance and inductive coupling, so as to achieve the double PCB 1/10 to 1/100. Signal each signal layer as close as possible to a power or ground layer. For the top and bottom surfaces, there are components, PCB with very short links, and many filling sites, which can be considered using inner lines.
For double-sided PCB, a tightly interleaved power and ground grid are used. The power cord is close to the ground wire and connects as much as possible between the vertical and horizontal lines or between the filling areas. One side of the grid size is less than or equal to 60mm, and if possible, the grid size should be less than 13mm. Make sure each circuit is as tight as possible. Put all the connectors aside as far as possible. If possible, introduce the power cord from the center of the card and away from the area directly affected by the ESD.
On all PCB layers under the connector that leads to the outside of the enclosure (easily hit by the ESD), place a wide enclosure or polygon and connect them at intervals of about 13mm. The mounting holes are positioned on the edge of the card, and the top and bottom pads of the unimpeded solder are connected to the chassis of the chassis around the mounting hole.
When PCB is assembled, do not apply any solder on top or bottom pads. Use a screw with an embedded washer to achieve close contact between the PCB and the metal case / shield or the rack on the ground.
The same "isolation zone" shall be provided between the chassis and the circuit of each floor; if possible, keep the interval of 0.64mm.
At the top and bottom of the card, near the mounting hole, connect the chassis to the circuit with 1.27mm wide wires every 100mm along the chassis ground wire. Adjacent to these connection points, a pad or mounting hole for mounting is placed between the chassis and the circuit. These ground connection can be used to keep the blade open, open, or jump beads / high frequency capacitance.
If the circuit board is not placed in a metal case or shield, it is not possible to solder the solder on the top of the circuit board and the ground wire of the lower chassis, so that they can be used as the discharge electrodes of the ESD arc.
Set a ring around the circuit in the following manner:
(1) in addition to the edge connector and the chassis, a circular path is placed 4 weeks across the perimeter.
(2) ensure that all layers have a circular width greater than 2.5mm.
(3) the rings are joined together at intervals of 13mm.
(4) the public connection of the ring with the multilayer circuit is common.
(5) for double sided panels mounted in metal enclosures or shielding devices, the ring shall be connected to the circuit in public. Double sided circuit should be no shielding ring connected to the chassis, the ground can not resist ring coated, so that the ring can act as a ESD discharge rod, in a ring (all layers) a position on at least put a 0.5mm wide gap, which can avoid the formation of a large loop. The distance of signal wiring from the ring shall not be less than 0.5mm.
