Antistatic discharge method for PCB circuit board design
In PCB circuit board design, anti-ESD PCB circuit board design can be realized through layering, proper layout and wiring and installation.By adjusting circuit board layout wiring, ESD can be well protected. Use a multilayer PCB circuit board as much as possible. Ground and power plane, and tightly spaced signal-ground lines reduce common mode impedance and inductive coupling to 1/10 to 1/100 of a double-sided circuit board,compared with double-sided circuit board.For the top and bottom surface are components, with very short wiring.
Static electricity from the human body, environment or even the inside of electronic devices can cause all kinds of damage to precise semiconductor chips, such as penetrating the thin insulation layer inside the components.Damaging the gate of MOSFET and CMOS components;Trigger lock in CMOS device;Short circuit reverse biased PN junction;Short circuit forward biased PN junction;Weld wire or aluminum wire inside a fusion active device.In order to eliminate the interference and damage of ESD to electronic equipment, various technical measures should be taken.
In PCB circuit board design, anti-ESD pcb design can be realized through layering, proper layout and wiring and installation.In the PCB circuit board design process, the vast majority of PCB circuit board design modifications can be limited to incremental and subtractive components by prediction.By adjusting PCB layout and wiring, ESD can be well protected.Here are some common precautions.
* Use a multilayer PCB circuit board as much as possible. Ground and power plane, and tightly spaced signal-ground lines reduce common mode impedance and inductive coupling to 1/10 to 1/100 of a double-sided PCB circuit board, compared with double-sided PCB circuit board.As close as possible to each signal layer next to a power layer or ground layer.For high-density PCB circuit boards with components on top and bottom surfaces, very short connectors, and lots of padding, consider using an inner layer.
* For double-sided PCB circuit board, tightly intertwined power and ground grids are used.Connect as many power lines as possible between vertical and horizontal lines or fill areas, close to ground.One side of the grid size is less than or equal to 60mm, if possible, the grid size should be less than 13mm.
* Make sure each circuit is as compact as possible.
* Put all connectors aside if possible.
* If possible, import the power cord from the center of the card and away from areas that are directly affected by ESD.
* On all PCB circuit board layers below the connector that leads to the outside of the chassis (which is easy to be hit by ESD directly), place wide chassis or polygonal fill fields and connect them with holes at approximately 13mm intervals.
*A mounting hole is placed on the edge of the card, and the top and bottom welding pads are connected to the chassis ground around the mounting hole with an unhindered flux.
* When PCB circuit board is assembled, do not apply any solder to the top or bottom of the solder pad.Use screws with built-in washers to achieve close contact between the PCB circuit board and the metal chassis/shield or ground surface support.
* Set the same “isolation zone” between the chassis ground and circuit ground of each floor;If possible, keep the spacing 0.64mm
* On the top and bottom floor of the card near the mounting hole, connect the chassis ground and circuit ground with 1.27mm wide wires along the chassis ground wire every 100mm.Adjacent to these connection points, a mounting pad or mounting hole is placed between the chassis ground and the circuit ground for installation.These ground connections can be cut with a blade to keep the circuit open, or with a magnetic bead/high frequency capacitor jumper
* If the PCB circuit boards are not in the metal case or shielding device, the top and bottom chassis ground wires of the PCB circuit boards shall not be coated with solder, so that they can be used as the discharge electrode of ESD arc.
to place a ring around the circuit in the following manner:
(1) in addition to the edge connector and chassis ground, put on the whole peripheral peripheral annular access.
(2) ensure that the annular width of all layers is greater than 2.5mm.
(3) connect the rings with holes every 13mm.
(4) connect the annular circuit with the common ground of the multi-layer circuit.
(5) for double panels mounted in metal chassis or shielding devices, the ring shall be connected to the circuit common ground.
Unshielded double-sided circuits shall be looped to the chassis floor, which shall not be coated with flux, so that the looped floor may serve as the discharge rod for the ESD and a minimum of 0.5mm wide clearance shall be placed at a position on the looped floor (all layers) to avoid the formation of a large loop.The distance between the signal wiring and the ring ground shall not be less than 0.5mm.
* A ground wire should be placed near each signal line in an area that can be directly hit by ESD
*I/O circuits should be as close to the corresponding connector as possible.
* Circuits susceptible to ESD should be placed near the center of the circuit so that other circuits can provide some shielding for them.
* Series resistance and magnetic beads are usually placed at the receiving end. For cable drivers that are vulnerable to ESD, series resistance or magnetic beads can also be considered to be placed at the driving end.
* A transient protector is usually placed at the receiving end.Connect the chassis floor with short, thick wire (length less than 5 times width, preferably less than 3 times width).The signal line and ground wire from the connector are connected directly to the transient protector before connecting to the rest of the circuit.
* Place the filter capacitor at the connector or within 25mm of the receiving circuit.
(1) connect the short and thick wire to the chassis ground or receiving circuit ground (length less than 5 times width, preferably less than 3 times width).
(2) the signal line and ground wire are connected to the capacitor and then to the receiving circuit.
* Make sure the signal lines are as short as possible.
* When the length of the signal line is greater than 300mm, a ground wire must be laid in parallel.
* Ensure that the area of the loop between the signal line and the corresponding loop is as small as possible.For long signal lines, the position of the signal line and ground wire should be changed every few centimeters to reduce the area of the loop.
* Drive signals from the central location of the network into multiple receiving circuits.
* Make sure that the loop area between the power supply and the ground is as small as possible, and place a high frequency capacitor close to each power pin of the IC chip.
* Place a high frequency bypass capacitor within 80mm of each connector.
* Where possible, fill unused areas with land, connecting all layers of fill space at 60mm intervals.
* Make sure to connect to the ground at two opposite ends of any large fill area (approximately greater than 25mm 6mm).
* When the opening length on the power supply or ground plane exceeds 8mm, connect both sides of the opening with a narrow line.
* Reset line, interrupt signal line or edge trigger signal line cannot be placed near the edge of PCB circuit board.
* Connect mounting holes to circuit common or isolate them.
(1) when the metal support must be used together with the metal shielding device or the chassis, a zero ohm resistance shall be adopted to realize the connection.
(2)confirm the size of the mounting hole to achieve the reliable installation of metal or plastic support. The top and bottom of the mounting hole shall be equipped with a large welding pad, and the soldering flux shall not be used on the bottom welding pad, and the bottom welding pad shall not be welded by wave soldering technology.
* Protected and unprotected signal lines cannot be arranged in parallel.
* Pay special attention to the wiring of reset, interrupt and control signal lines.
(1) high frequency filtering should be adopted.
(2) stay away from input and output circuits.
(3) keep away from the edge of the circuit board.
* PCB circuit board should be inserted into the chassis, not installed in the open position or internal seam.
* Pay attention to the wiring under the magnetic beads, between the pads and the signal lines that may touch the magnetic beads.Some beads conduct electricity so good that they can create unexpected paths.
* If a chassis or main board contains several boards, place the boards that are most sensitive to static electricity in the middle place.
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