A comprehensive summary of common PCB board design methods and measures to anti-ESD
1, as much as possible the use of multi-layer PCB
Compared to double-sided PCBs, the ground plane and power plane, as well as the closely spaced signal-to-ground spacing, reduce common mode impedance and inductive coupling to 1/10 to 1/100 the double-sided PCB. Try to place each signal layer close to a power or ground plane. For components on both the top and bottom surfaces, with very short connections and many fill-in, high-density PCBs, consider lining.
2, for double-sided PCB, to use closely intertwined power and ground grid.
Place the power cord close to the ground and connect as much as possible between the vertical and horizontal lines or fill area. The grid size on one side is 60 mm or less, and if possible, the grid size should be less than 13 mm.
3, to ensure that each circuit as compact as possible.
4, as far as possible all the connectors are aside.
5, in each floor of the chassis and circuit ground, to set the same “isolation zone”; if possible, to maintain the separation distance of 0.64mm.
6, PCB assembly, do not apply any solder on the top or bottom pads.
Use screws with built-in washers to make the PCB come into close contact with the metal chassis / shield or the bracket on the ground plane.
- If possible, introduce the power cord from the center of the card and away from areas prone to ESD
- Place wide chassis or polygons on all PCB layers leading to connectors outside the chassis (easily hit directly by ESD) and connect them with vias at a distance of approximately 13 mm together.
- Place the mounting holes on the edges of the card with the top and bottom pads of the solderless solder around the mounting holes to the chassis ground.
10, in the top and bottom of the card near the mounting hole location, every 100mm along the chassis ground and circuit ground with 1.27mm wide line connected together. Adjacent to these connection points, place pads or mounting holes for mounting between chassis ground and circuit ground. These ground connections can be razor-cut to keep open or jumpered with beads / HF capacitors.
11, If the circuit board will not be placed in a metal chassis or shielding device, the top of the circuit board and the bottom chassis ground can not be coated with solder resist, so that they can be used as ESD arc discharge electrode.
12 Place a ring around the circuit in the following way:
(1) Place an annular passage all around the periphery except for the edge connector and the chassis ground.
(2) Make sure the annular width of all layers is greater than 2.5mm.
(3) Each 13mm ring will be connected with the hole.
(4) connects the loop together with the multilayer circuit in common.
(5) A double panel mounted in a metal enclosure or shield should be connected in a loop to the circuit. The unshielded double-sided circuit should then be connected to the chassis ground in a ring shape that can not be toroidally coated so that the toroid can act as a discharge bar for the ESD, placing at least one ring somewhere on all layers 0.5mm wide gap, so you can avoid the formation of a large loop. Signal wiring from the annular distance of not less than 0.5mm.
13, in the area can be directly hit by ESD, every signal line should be laid a ground.
14, I / O circuit as close as possible to the corresponding connector.
15, for ESD-sensitive circuits, should be placed near the center of the circuit area, so that other circuits can provide them with some shielding effect.
16, usually placed in the receiver transient protection. Use short and thick wires (less than 5 times the length, preferably less than 3 times the width) to the chassis ground. The signal and ground wires coming from the connector should be connected directly to the transient protector before they can be connected to the rest of the circuit.
- It is common to place resistors and beads in series at the receiver end. For those cable drivers that are vulnerable to ESD, consider placing resistors or beads in series on the driver end.
18 at the connector or away from the receiving circuit 25mm range, to place the filter capacitor.
(1) Use a short, thick wire to connect to the chassis ground or receive ground (less than 5 times the length, preferably less than 3 times the width).
(2) Connect the signal cable and ground cable first to the capacitor and then to the receiving circuit.
18, to ensure that the signal line as short as possible.
19, the length of the signal line is greater than 300mm, be sure to parallel a cloth ground.
20, to ensure that the loop area between the signal line and the corresponding loop as small as possible. For long signal lines every few centimeters will have to replace the location of signal lines and ground to reduce the loop area.
21, from the central location of the network drive signal into multiple receiver circuits.
22, where possible, to fill the unused area, every 60mm distance will be filled with all layers connected.
23,Make sure that the loop area between the power supply and ground is as small as possible and place a high frequency capacitor near each power pin of the IC chip.
24,Place a high frequency bypass capacitor within 80mm of each connector.
25, reset line, interrupt signal line or edge trigger signal line can not be arranged near the edge of the PCB.
26, to ensure that in any large ground filling area (about greater than 25mm × 6mm) at the two opposite ends of the location to be connected with the ground.
27, the power or ground plane when the opening length exceeds 8mm, with a narrow line to connect the two sides of the opening.
28, the installation hole with the circuit connected to the public, or to isolate them.
(1) A metal bracket must be used with a metal shield or chassis to connect with a zero ohm resistor.
(2) Determine the size of the mounting holes for reliable mounting of metal or plastic brackets. Use large pads on the top and bottom mounting holes. Solder resist should not be used on the bottom pads. Ensure that the bottom pads are not soldered by wave soldering welding.
29, can not be protected signal lines and unprotected signal lines arranged in parallel.
30, pay special attention to reset, interrupt and control signal wiring.
(1) to use high-frequency filtering.
(2) Keep away from the input and output circuits.
(3) away from the edge of the circuit board.
31, PCB to be inserted into the chassis, do not install in the opening position or internal seams.
32, pay attention to the magnetic beads, the pads and the signal lines may be exposed to the wiring of the magnetic beads. Some beads behave quite well and can have an unexpected conductive path.
33, if a chassis or motherboard to be built a few boards, the most sensitive to the static electricity should be placed in the middle of the circuit board.