Electronic Design - PCB circuit board wiring skills explained

PCB is also called printed circuit board (PCB), which can realize circuit connection and function realization between electronic components, and it is also an important part of power supply circuit design. Today, I will use this article to introduce the basic rules of PCB layout.

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. Do not mount components, devices, screws and other mounting holes within 1.27mm around non-mounting holes such as positioning holes, standard holes, and 3.5mm (for M2.5), 4mm (for M3), and do not mount components;

3. Avoid placing via holes under the components such as horizontally mounted resistors, inductors (plug-ins), electrolytic capacitors, etc., so as to avoid short circuits between 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 not touch other components, can not 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 dianlu board as much 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 difference in density 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 SMD pads 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. As far as possible, the polarized devices should be consistent with the polarity marking direction on the same board.

Second, component wiring rules

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

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 is not less than 30mil;

4. Dual in-line: 60mil pad, 40mil aperture;

1/4W resistance: 51*55mil (0805 surface mount); when in-line, the pad is 62mil, and the aperture is 42mil;

Infinite capacitance: 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 must 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 with a very high microcontroller clock frequency and a very fast bus cycle.

(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.