PCB Technical - PCB circuit board layout and routing two major points

PCB circuit board is also called printed circuit board (Printed Circuit Board), which can realize circuit connection and function realization between electronic components, and it is also an important part of power supply circuit design.

1. Basic rules of component layout

1. Layout according to circuit modules, and related circuits that achieve the same function are called a module. The components in the circuit module should adopt the principle of nearby concentration, and the digital circuit and the analog circuit should be separated;

2. No components or devices shall be mounted within 1.27mm around non-mounting holes such as positioning holes, standard holes, and 3.5mm (for M2.5) and 4mm (for M3) components shall not be mounted around the mounting holes such as screws;

3. Avoid placing via holes under the horizontally mounted resistors, inductors (plug-ins), electrolytic capacitors and other components to avoid short-circuiting the vias and the component housing 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 mounting component pad and the outside of the adjacent interposing component is greater than 2mm;

6. Metal shell components and metal parts (shielding boxes, etc.) can't touch other components, can't be close to printed lines, pads, and their spacing should be greater than 2mm. The size of the positioning hole, fastener installation hole, oval hole and other square holes in the board from the edge of the board is greater than 3mm;

7. The heating element should not be in close proximity to the wire and the heat-sensitive element; the high-heating device should be evenly distributed;

8. The power socket should be arranged around the printed board as far as possible, and the power socket and the bus bar terminal connected to it should be arranged on the same side. Particular care should be taken not to arrange power sockets and other welding connectors between the connectors to facilitate the welding of these sockets and connectors, as well as the design and tie-up of power cables. The arrangement spacing of power sockets and welding connectors should be considered to facilitate the plugging and unplugging of power plugs;

9. Arrangement of other components:

All IC components are aligned on one side, and the polarity of the polar components is clearly marked. The polarity of the same printed board cannot be marked in more than two directions. When two directions appear, the two directions are perpendicular to each other;

10. The wiring on the board surface should be dense and dense. When the density difference is too large, it should be filled with mesh copper foil, and the grid should be greater than 8mil (or 0.2mm);

11. There should be no through-holes on the PCB patch pad to avoid the loss of solder paste and cause false soldering of the components. 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. The polarized devices should be consistent as far as possible on the direction of the polarity marking on the same board.

Two, component wiring rules

1. Draw the wiring area within 1mm from the edge of the PCB board, and within 1mm around the mounting hole, wiring is forbidden;

2. The power cord 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 is not less than 30mil;

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

5. Note that the power line and the ground line should be as radial as possible, and the signal line 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?

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

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

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

(3) A system containing a weak analog signal circuit and a high-precision A/D conversion circuit.