PCB Tech - Problems to be paid attention to when designing PCB wiring

PCB layout rules

1. Under normal circumstances, all components should be arranged on the same surface of the printed circuit board, only the top layer of components is too dense, to put some highly limited and small heat devices, such as chip resistance, chip capacitance, chip IC, etc., on the bottom.

2. On the premise of ensuring the electrical performance, the components should be placed on the grid and arranged parallel or vertically to each other, so as to be neat and beautiful. Overlapping components are not allowed under general circumstances; The arrangement of components should be compact, and the components should be evenly distributed and uniform in density throughout the layout.

3. The small spacing between the adjacent pads of different components on the circuit board should be above 1MM.

4. Generally not less than 2MM from the edge of the circuit board. The best shape of the circuit board is a rectangle, length to width ratio of 3:2 or 4:3. When the circuit board size is greater than 200MM by 150MM, the mechanical strength that the circuit board can withstand should be considered.

PCB design and setup skills

PCB design in different stages need to carry out different point Settings, in the layout stage can use large grid points for device layout.

For large devices such as IC and non-positioning connectors, grid points of 50~100mil can be used for layout, while for passive small devices such as resistor capacitance and inductor, grid points of 25mil can be used for layout. Large grid points are good for device alignment and beautiful layout.

PCB design layout skills

In PCB layout design, the unit of the circuit board should be analyzed, and the layout design should be carried out according to the function. When all the components of the circuit are laid out, the following principles should be followed:

a. Arrange the position of each functional circuit unit according to the circuit process, so that the layout is convenient for signal flow, and keep the signal in the same direction as far as possible.

b. to the components of each functional unit as the center, around him to carry out the layout. Components should be uniformly, integrally and compactly arranged on the PCB to minimize and shorten leads and connections between components.

c. For circuits working at high frequencies, distribution parameters between components should be considered. General circuit components should be arranged in parallel as far as possible, so that not only beautiful, but also easy to install dry, easy to mass production.

The following points should be paid attention to when designing PCB wiring:

(1) The wire length should be as short as possible to minimize the inductance of the lead. In low-frequency circuits, multipoint grounding is avoided because the ground current of all circuits flows through a common grounding impedance or grounding plane.

The public ground wire should be arranged as far as possible in the printed circuit board edge part. As much as possible on the circuit board should keep copper foil as ground wire, can enhance the shielding ability.

(3) Double-layer plates can use ground surface, the purpose of the ground surface is to provide a low impedance ground.

Multilayer printed circuit board, can be set up ground, ground design into a network. The spacing of ground grids should not be too large, because one of the main functions of ground grids is to provide signal backflow path. If the spacing of ground grids is too large, a large signal loop area will be formed. Large loop areas can cause radiation and sensitivity problems. In addition, the signal backflow actually takes the path of small loop area, and other ground wires do not play a role.

The ground surface can make the radiation loop small.