Suggestions for EMC design of PCB layout

2023-09-19 10:32

Accordingto the PCB design process, after the PCB layout was completed, a rigorousreview process is required to determine whether the designed product meets theESD or EMI requirements. Excluding schematic design, PCB design generallyrequired to review both layout and wiring. DYC Electronics will introduce EMCdesign suggestions for PCB layout.


EMC Design Layout InspectionRecommendations

1. Suggestions for overalllayout inspection

1) Analog, digital, power, and protection circuits should beseparated, and there should be no overlap on the three-dimensional surface;

2) High speed, medium speed, and low speed circuits should beseparated;

3) Strong current, high voltage, and strong radiation componentsshould be kept away from small current, low voltage, and sensitive components;

4) Multi layer board design must have separate power and groundplanes;

5) For heatsensitive components (including liquid electrolytic capacitors and oscillators),try to stay away from high-power components, heat sinks, and other heat sourcesas much as possible.

2. Suggestions forinterface and protection layout inspection

1) The sequence of general power supplylightning protection devices is: varistor → fuse → suppression diode → EMIfilter → inductance or common mode inductance, and for any missing componentsin the schematic diagram, the layout should be extended accordingly;

2) The general order of protective devicesfor interface signals is: ESD (TVS transistor) → isolation transformer → commonmode inductance → capacitance → resistance. For any missing components in theschematic diagram, a sequential layout is carried out;

3) The level conversion chip (such asRS232) should be placed close to the connector (such as the serial port);

4) Devices that are susceptible to ESDinterference, such as NMOS and CMOS devices, should be kept as far away fromareas that are susceptible to ESD interference (such as the edge area of asingle board) as possible.

3. Suggestions forchecking clock circuit layout

1) The filter of the clock circuit(preferably using a "π" type filter) should be close to the powerinput pin of the clock circuit;

2) The layout of crystals, oscillators,and clock distributors should be kept away from high-power components, heatsinks, and other heating devices;

3) Crystals, oscillators, and clockdividers should be as close as possible to related IC devices;

4) The distance between the oscillator andthe board edge and the interface device should be greater than 1 inch.

4. Suggestion forchecking the layout of switching power supply

1) Switching power supply should be keptaway from AD/DA converters, analog devices, sensitive devices, and clockdevices;

2) Strictly follow the requirements of theschematic diagram for PCB layout, and do not randomly place the capacitors ofthe switching power supply;

3) The PCB layout of the switching powersupply should be compact, and the input/output should be separated.

5. Suggestion forchecking the layout of capacitors and filter components

1) In principle, each power pin should beplaced with a 0.1uf small capacitor, and an integrated circuit should be placedwith one or more 10uf large capacitors, which can be increased or decreasedaccording to specific circumstances;

2) Capacitors must be placed close to thepower pins, and capacitors with smaller capacitance values should be placedcloser to the power pins;

3) The EMI filter should be close to theinput port of the chip power supply.

6. Suggestions forstack inspection

1) Multilayer boards (four or more layers)have at least one continuous and complete ground plane used to control theimpedance and signal quality of the PCB;

2) Place the power supply plane and groundplane close to each other;

3) Try to avoid two signal layers beingadjacent to each other as much as possible. If the distance between the twosignal layers is increased, and the wiring should be misaligned and notoverlapped. Otherwise, later wiring may cause crosstalk;

4) Avoid adjacent power supply planes,especially those caused by signal layer power supply laying;

7. Other designinspection suggestions

1) When the entire machine is designed asa floating equipment, it is recommended not to design each interfaceseparately;

2) When the machine casing is made ofmetal, the power supply is three holes, and it is required that the metalcasing must be well connected to the ground.