PCB circuit board composition, design, process, flow and element placement and wiring principles

Everyone is very familiar with the word PCB circuit board circuit, some understand the composition of PCB circuit board, some understand the design steps of PCB circuit board, and some understand the production process of PCB circuit board... but there is no comprehensive understanding of the composition, design, process, process, element placement and wiring principles of the whole PCB circuit board, and the matters needing attention in the later period. Mu Wo Technology has integrated and listed this set. Let's follow Xiao Bian to learn!

The composition of PCB circuit board: circuit and drawing: circuit is used as a tool for conduction between the original components, and a large copper surface will be additionally designed as a grounding and power supply layer. The circuit and the drawing are made at the same time. Dielectric layer: used to maintain the insulation between the circuit and each layer, commonly known as the base material; Hole: The through hole can make more than two layers of lines conduct to each other, the larger through hole is used as the plug-in of parts, and the non-through hole is usually used for surface mount positioning and fixing screws during assembly. Soldering resistance ink: not all copper surfaces need tin parts, therefore, the non-tin-eating area will print a layer of material (usually epoxy resin) that isolates the copper surface from eating tin to avoid short circuits between non-tin-eating lines. According to different processes, it is divided into green oil, red oil and blue oil. Silk screen printing: this is an unnecessary composition. its main function is to mark the name and position frame of each part on the circuit board for convenient maintenance and identification after assembly. Surface treatment: as the copper surface is easily oxidized in the general environment, tin cannot be applied (poor soldering), it will be protected on the copper surface to be tin. The protection methods include tin spraying, gold, silver, tin, and organic solder. Each method has its advantages and disadvantages, collectively referred to as surface treatment.

PCB circuit board design steps:

Circuit schematic design: circuit schematic design is mainly the use of Protel DXP schematic editor to draw the schematic diagram.

Generation of network report: network report is a report showing the link relationship between circuit principle and various components. it is a bridge and link connecting circuit schematic diagram design and circuit board design. through the network report of circuit schematic diagram, the link between components can be quickly found, thus providing convenience for the following PCB design.

PCB circuit board design: PCB design is based on the circuit schematic diagram to achieve the required functions, design PCB diagram, need to consider many factors, including mechanical structure, external connection layout, component layout, wiring, heat dissipation, electromagnetic compatibility and so on. To finally complete this step often requires countless changes to the circuit schematic.

Production of PCBA control board: after the components are purchased and the PCB board is obtained, according to the schematic diagram, through the process of SMT loading, welding various components and DIP plug-ins, our control board is completed.

Principle of component placement: First, place components that are closely matched with the structure, such as power sockets, indicator lights, switches, connectors, interfaces, etc. Secondly, place special components, such as large components, heavy components, heating components, IC, etc. Finally, place small components; When laying out components, wiring should be considered and layout design conducive to wiring should be selected as far as possible;

The crystal oscillator should be placed close to the IC; The layout of the IC decoupling capacitor should be as close as possible to the power pin of the IC, and the loop formed between the power supply and the ground should be the shortest. Heating elements should generally be evenly distributed to facilitate the heat dissipation of the single board and the whole machine. Temperature sensitive devices except temperature detection elements should be far away from components with large heat generation;

Principles of routing

1. The high-speed signal trace shall be as short as possible, and the key signal trace shall be as short as possible;

2. Don't make too many vias for one line, and don't make more than two vias;

3, the line corner should be as much as possible greater than 90 degrees, put an end to the corner below 90 degrees, but also try to use 90 degrees corner;

4, double-panel wiring, the two sides of the wire should be perpendicular to each other, oblique, or bent to avoid parallel to each other, in order to reduce parasitic coupling;

5. Audio input lines should be of equal length, two lines should be placed close to each other, and audio lines should be outsourced with ground lines;

6. No wiring can be routed under the power amplifier IC. More vias can be punched under the power amplifier IC to connect with GND;

7. There is no ground line layer in the double-sided board. The ground line of the crystal oscillator capacitor should be connected to the GND pin closest to the crystal oscillator on the device with the shortest possible short line, and the vias should be minimized;

8. For the power cord and USB charging input, thick wire ("= 1mm) should be used. Copper should be laid on both sides of the via hole, and then several more via holes should be laid at the copper hole;