What is a PCB Circuit Board?Posted on 2020-07-10
PCB circuit board, also known as printed circuit boards, are providers of electrical connections for electronic components. Its development has a history of more than 100 years. Its design is mainly layout design, and the main advantage of using a circuit board is to greatly reduce wiring and assembly errors, and improve the level of automation and production labor rate.
The composition of the PCB circuit board
- Circuit and Pattern: The circuit is used as a tool for conduction between the originals. In the design, a large copper surface will be additionally designed as a ground and power layer. The lines and drawings are made at the same time.
- Dielectric: used to maintain the insulation between the circuit and each layer, commonly known as the substrate.
- Hole: The through-hole can make the lines above two levels to connect with each other, the larger through-hole is used as a part insert, and the non-through hole is usually used as a surface mount It is used for positioning and fixing screws during assembly.
- Solder resistant /Solder Mask: Not all copper surfaces need to eat tin on the parts, so the non-tin eating area will be printed with a layer to isolate the copper surface eating tin material (usually epoxy resin) to avoid There is a short circuit between the lines not eating tin. According to different processes, it is divided into green oil, red oil and blue oil.
- Screen printing (Legend / Marking/Silkscreen): This is a non-essential component. The main function is to mark the name and location frame of each part on the circuit board, which is convenient for maintenance and identification after assembly.
- Surface finish: Since the copper surface is easily oxidized in the general environment, it can not be tinned (poor solderability), so it will be protected on the copper surface that will eat tin. The protection methods are HASL, ENIG, immersion silver, immersion tin, OSP. The methods have their own advantages and disadvantages, which are collectively called surface treatment.
PCB circuit board design steps
The basic design process of the circuit board can be divided into the following four steps:
The design of the circuit schematic diagram: The design of the circuit schematic diagram mainly uses the schematic diagram editor to draw the schematic diagram.
Generate a network report: A network report is a report that shows the relationship between the circuit principle and the various components in it. It is a bridge and link between the circuit schematic design and the circuit board design. Through the network report of the circuit schematic, you can quickly find the element The connection between the devices, thus providing convenience for the subsequent PCB design.
Printed circuit board design: The printed circuit board design is what we usually call the PCB design. It is the final form of the circuit schematic. The related design of this part is more difficult than the design of the circuit schematic. We can complete this part of the design with the help of powerful design functions.
Generate printed circuit board reports: After the printed circuit board design is completed, various reports need to be generated. For example, generate pin reports, circuit board information reports, network status reports, etc., and finally print out the printed circuit diagram.
PCB circuit board design considerations
1. Antenna design
- The wiring from the Bluetooth IC to the antenna should be smooth or straight;
- There should be no devices, wiring and copper laying around the effective part of the antenna and its lower layer (ie the back);
- The antenna is required to be designed on the edge of the PCB, facing the front panel as much as possible, and it is required to avoid iron structural parts around;
- Choose the type of antenna according to the size of the PCB board, choose the inverted F antenna when the board is large, and choose the snake antenna when the board is small;
2. Second, the component placement principle
- The general order of component placement: First, place components that closely match the structure. Such as power sockets, indicators, switches, connectors, interfaces, etc. Second, place special components, such as large components, heavy components , Heat-generating components, IC, etc. Finally, place small components; layout should consider wiring, try to choose layout layout that is conducive to wiring;
- The crystal should be placed close to the IC;
- The layout of the IC decoupling capacitor should be as close as possible to the power supply pin of the IC, and the shortest loop formed between it and the power supply and ground;
- The heating elements should be evenly distributed to facilitate heat dissipation of the single board and the whole machine. Temperature-sensitive devices other than the temperature detection elements should be kept away from components that generate large amounts of heat;
3. Wiring principles
- Keep high-speed signal traces as short as possible, and key signal traces as short as possible;
- Don’t make too many vias for one trace, and don’t exceed two vias;
- The routing corners should be greater than 90 degrees as much as possible, and corners below 90 degrees should be eliminated, and 90-degree corners should be used as little as possible;
- When double-sided wiring, the wires on both sides should be perpendicular, diagonal or curved to avoid parallel to reduce parasitic coupling;
- The audio input wires should be of equal length, the two wires should be placed close to each other, and the audio wire should be wrapped with a ground wire;
- The power amplifier IC can not be routed under the power amplifier IC, and many vias are connected to GND;
- There is no ground layer in the double-sided board. The ground wire of the crystal capacitor should be connected to the GND pin closest to the crystal on the device with as short a wire as possible, and the vias should be minimized;
- Power cord, USB charging input should go thick line (》=1mm), copper on both sides of the hole, then make a few more holes in the copper;
Under normal circumstances, the power cord and ground wire should be wired first to ensure the electrical performance of the circuit board. To the extent possible, widen the width of the power and ground wires as much as possible. It is better that the ground wire is wider than the power wire. Their relationship is: ground wire> power wire> signal wire, usually the signal wire width is: 0.2 ~ 0.3mm , The thinnest width can reach 0.05～0.07mm, the power cord is generally 1.2～2.5mm.
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