Printed Circuit Board Design and Related Steps (I)

SMT circuit board is one of the indispensable components in surface mount design. The SMT circuit board is a support for circuit components and devices in electronic products, which realizes the electrical connection between circuit components and devices. With the development of electronic technology, the PCB board is getting smaller and smaller, the density is getting higher and higher, and the number of PCB layers continues to increase. Therefore, PCBs are required to have overall layout, anti-interference ability, process, and manufacturability. Higher and higher.

The major steps in the design of printed circuit boards;

1: Draw the schematic.

2: The creation of a component library.

3: Establish the network connection between the schematic and the components on the printed board.

4: wiring and layout.

5: Create printed board production usage data and placement production usage data.

The following issues must be considered in the design of the printed circuit board:

1. Make sure that the circuit diagram component diagram is consistent with the physical object and the correctness of the network connection in the circuit schematic.

2. The design of the printed circuit board not only considers the network connection relationship of the schematic diagram, but also considers some requirements of the circuit engineering. The requirements of the circuit engineering are mainly the widths of the power lines, ground lines and other wires, the connection of the lines, High-frequency characteristics of some components, component impedance, anti-jamming, etc.

3. Requirements for the installation of the printed circuit board assembly system, mainly considering that the mounting holes, plugs, positioning holes, reference points, etc. must meet the requirements, the placement of various components and the accurate installation in the specified position, and at the same time to facilitate Installation, system commissioning, and ventilation and heat dissipation.

4. The manufacturability of the printed circuit board and its technological requirements must be familiar with the design specifications and meet the requirements of the production process so that the designed printed circuit board can be smoothly produced.

5, in consideration of components in the production of easy installation, debugging, repair, and printed circuit board graphics, pads, vias and other standards to ensure that the components will not collide, and easy installation.

6, the purpose of designing the printed circuit board is mainly application, so we must consider its practicability and reliability, and at the same time reduce the board area and area of ​​the printed circuit board, so as to reduce the cost, the appropriate larger pad, Vias, traces, etc. are conducive to improving reliability, reducing via holes, optimizing alignment, making them dense and uniform, and having good consistency, so that the overall layout of the board surface is aesthetically pleasing.

First, to make the designed circuit board achieve the intended purpose, the overall layout of the printed circuit board and the placement of components play a key role. It directly affects the installation, reliability, ventilation, and heat dissipation of the entire printed circuit board. Through rate.

The outer dimensions of the printed circuit board are given priority. When the PCB size is too large, the printed lines are long, the impedance increases, the anti-noise ability decreases, and the cost increases. When the size is too small, the heat dissipation is not good, and the adjacent lines are susceptible to interference. Therefore, First give a reasonable position for the size and shape of the PCB. To determine the location of the special components and the unit circuit, etc., the entire circuit is divided into several unit circuits or modules according to the flow of the circuit, and the core components of each unit circuit (such as integrated circuits) are centered, and other components are pressed. A certain order is evenly and neatly arranged on the PCB board, but not too close to these large components, there must be a certain distance, especially some relatively large, relatively high components around to maintain a certain distance, which is conducive to welding And repair. For a power-intensive integrated circuit, consider the color heat sink, leave enough space for it, and place it in a good position for the heat dissipation of the printed board. At the same time, do not be too concentrated. Several large components must have a certain distance on the same board, and they must be oriented in the direction of 45 degrees. Some smaller integrated circuits such as SOPs should be arranged along the axial direction. The components are arranged vertically in the axial direction, all of which are relative to the direction of the PCB's production process. This allows the components to be regularly arranged, thereby reducing the defects generated in the welding. The LEDs used for display should be considered at the edge of the printed board because they are to be used during the application.

Some switches, fine-tuning components, etc. should be placed in an easy-to-operate place. In the same frequency circuit should consider the distribution parameters between components, general high-frequency circuits should consider the distribution parameters between components, the general circuit as much as possible parallel arrangement of components, this is not only beautiful, but also easy to install welding, at the same time Easy to batch production, components located on the edge of the circuit board must be 3-5 cm from the edge. Considering the position of the component, consider the thermal expansion coefficient, thermal conductivity, heat resistance, and flexural strength of the PCB, so as to avoid adverse effects on the component or PCB during production.