PCB Blog - 10-year-old engineer summarizes PCB board wiring tricks

1. Basic Rules of PCB board Component Layout
1) Layout according to the circuit module, the related circuit that realizes the same function is called a module, the components in the circuit module should adopt the principle of nearest concentration, and the digital circuit and the analog circuit should be separated at the same time;
2) Do not mount components and devices within 1.27mm around non-mounting holes such as positioning holes and standard holes, and do not mount components within 3.5mm (for M2.5) and 4mm (for M3) around mounting holes such as screws;
3) Avoid placing vias below components such as horizontally mounted resistors, inductors (plug-ins), and electrolytic capacitors to avoid short circuits between the vias and the component shell after wave soldering;
4) The distance between the outside of the component and the edge of the board is 5mm;
5) The distance between the outside of the pad of the mounted component and the outside of the adjacent component is greater than 2mm;
6) Metal shell components and metal parts (shielding boxes, etc.) cannot touch other components, and cannot be close to printed lines and pads, and the spacing should be greater than 2mm. The size of the positioning holes, fastener installation holes, elliptical holes, and other square holes in the plate is greater than 3mm from the edge of the plate;
7) The heating element cannot be close to the wire and the thermal element; the high-heating element should be evenly distributed;
8) The power socket should be arranged around the printed board as much as possible, and the bus bar terminals connected to the power socket should be arranged on the same side. Special care should be taken not to arrange power sockets and other soldered connectors between the connectors, in order to facilitate the soldering of these sockets and connectors, and the design and tying of power cables. The arrangement spacing of power sockets and welding connectors should be considered to facilitate the insertion and removal of power plugs;
9) Arrangement of other components: All IC components are aligned on one side, polar components are marked clearly, and the polarity marking on the same printed board should not be more than two directions. When two directions appear, the two directions are perpendicular to each other. ;
10) The wiring on the board should be properly dense. When the difference in density is too large, it should be filled with mesh copper foil, and the mesh should be greater than 8mil (or 0.2mm);
11) There should be no through-holes on the patch pads, so as to avoid the loss of solder paste and cause the components to be soldered. Important signal lines are not allowed to pass between the socket pins;
12) The patch is aligned on one side, the character direction is the same, and the packaging direction is the same;
13) For devices with polarity, the direction of polarity marking on the same board should be as consistent as possible.

2. Component wiring rules

1. In the area where the wiring area is ≤1mm from the edge of the PCB, and within 1mm around the mounting hole, wiring is prohibited;

2. The power line should be as wide as possible and should not be less than 18mil; the signal line width should not be less than 12mil; the cpu input and output lines should not be less than 10mil (or 8mil); the line spacing should not be less than 10mil;

3. The normal via hole is not less than 30mil;

4. Dual in-line: pad 60mil, aperture 40mil; 1/4W resistor: 51*55mil (0805 surface mount); in-line pad 62mil, aperture 42mil; electrodeless capacitor: 51*55mil (0805 surface mount); When in-line, the pad is 50mil, and the aperture is 28mil;

5. Note that the power wire and the ground wire should be as radial as possible, and the signal wire should not be looped.

How to improve anti-interference ability and electromagnetic compatibility?

How to improve anti-interference ability and electromagnetic compatibility when developing electronic products with processors?

1. The following systems should pay special attention to anti-electromagnetic interference:

1) A system in which the microcontroller clock frequency is particularly high and the bus cycle is particularly fast.

2) The system contains high-power, high-current drive circuits, such as spark-generating relays, high-current switches, etc.

3) Systems with weak analog signal circuits and high A/D conversion circuits.

3. Experience in reducing noise and electromagnetic interference.

1) If you can use low-speed chips, you don’t need high-speed chips. High-speed chips are used in key places.

2) A resistor can be used in series to reduce the transition rate of the upper and lower edges of the control circuit.

3) Try to provide some form of damping for relays etc.

4) Use a frequency clock that meets the system requirements.

5) The clock generator is as close as possible to the device using the clock. The quartz crystal oscillator case should be grounded.

6) Circle the clock area with a ground wire, and keep the clock wire as short as possible.

7) The I/O drive circuit should be as close as possible to the edge of the printed board so that it can leave the printed board as soon as possible. The signal entering the printed board should be filtered, and the signal from the high-noise area should also be filtered. At the same time, the method of serial terminal resistance should be used to reduce the signal reflection.

8) The useless end of the MCD should be connected to high, grounded, or defined as an output end. The end of the integrated circuit that should be connected to the power supply ground should be connected, and should not be left floating.

9) Do not float the input terminal of the gate circuit that is not in use, the positive input terminal of the operational amplifier that is not in use is grounded, and the negative input terminal is connected to the output terminal.

10) The printed board should use 45-fold lines instead of 90-fold lines as much as possible to reduce the external emission and coupling of high-frequency signals.

11) The printed board is divided according to frequency and current switching characteristics, and the distance between noise components and non-noise components should be farther.

12) Use a single-point power supply and single-point grounding for single-sided and double-sided boards, and the power line and the ground line should be as thick as possible. If the economy can afford it, use a multi-layer board to reduce the capacitive inductance of the power supply and ground.

13) Clock, bus, and chip select signals should be kept away from I/O lines and connectors.

14) The analog voltage input line and the reference voltage terminal should be kept as far away as possible from the digital circuit signal line, especially the clock.

15) For A/D devices, the digital part and the analog part would rather be unified rather than crossed.

16) The clock line perpendicular to the I/O line has less interference than the parallel I/O line, and the clock component pins are far away from the I/O cable.

17) The component pins should be as short as possible, and the decoupling capacitor pins should be as short as possible.

18) The key lines should be as thick as possible, and protective ground should be added on both sides. High-speed lines should be short and straight.

19) The lines sensitive to noise should not be parallel to high current, high-speed switching lines.

20) Do not route wires under the quartz crystal and under noise-sensitive devices.

21) Weak signal circuits, do not form current loops around low-frequency circuits.

22) Do not form a loop for any signal. If it is unavoidable, make the loop area as small as possible.

23) One decoupling capacitor per IC. A small high-frequency bypass capacitor should be added beside each electrolytic capacitor.

24) Use large-capacity tantalum capacitors or polycooled capacitors instead of electrolytic capacitors as circuit charges and discharge energy storage capacitors. When using tubular capacitors, the case should be grounded on PCB board.