Printed Circuit Board Design
SMT circuit board is one of the indispensable components in surface mount design. SMT circuit board is the support of circuit components and devices in electronic products, which realizes the electrical connection between circuit components and devices. With the development of electronic technology, The volume of PCB boards is getting smaller and smaller, the density is getting higher and higher, and the layers of PCB boards are constantly increasing. Therefore, PCBs are required to have higher and higher requirements in terms of overall layout, anti-interference ability, process and manufacturability.
The main steps of PCB design;
1: Draw the schematic diagram.
2: Creation of component library.
3: Establish the network connection relationship between the schematic diagram and the components on the printed board.
4: Wiring and layout.
5: Create printed board production and use data and placement production and use data.
The following issues should be considered in the design process of printed circuit boards:
It is necessary to ensure that the graphics of the components in the circuit schematic diagram are consistent with the actual objects and that the network connections in the circuit schematic diagram are correct.
The design of printed circuit boards not only considers the network connection relationship of the schematic diagram, but also considers some requirements of circuit engineering. The requirements of circuit engineering are mainly the width of power lines, ground wires and other wires, the connection of lines, some High-frequency characteristics of components, impedance of components, anti-interference, etc.
The design of printed circuit boards not only considers the network connection relationship of the schematic diagram, but also considers some requirements of circuit engineering. The requirements of circuit engineering are mainly the width of power lines, ground wires and other wires, the connection of lines, some High-frequency characteristics of components, impedance of components, anti-interference, etc.
The requirements for the installation of the printed circuit board whole system mainly consider the installation holes, plugs, positioning holes, reference points, etc.
It must meet the requirements, the placement of various components and accurate installation in the specified position, and at the same time, it must be convenient for installation, system debugging, and ventilation and heat dissipation.
Manufacturability of printed circuit boards and its manufacturability requirements, to be familiar with the design specifications and meet the requirements of production
Process requirements, so that the designed printed circuit board can be produced smoothly.
Considering that the components are easy to install, debug, and repair in production, and at the same time, the graphics on the printed circuit board, soldering, etc.
Plates, vias, etc. must be standard to ensure that components do not collide and are easily installed.
The purpose of designing a printed circuit board is mainly for application, so we have to consider its practicability and reliability,
At the same time, the layer and area of the printed circuit board are reduced to reduce the cost. Appropriately larger pads, through holes, and wiring are conducive to improving reliability, reducing vias, optimizing wiring, and making it evenly dense. , the consistency is good, so that the overall layout of the board is more beautiful.
First, to make the designed circuit board achieve the expected purpose, the overall layout of the printed circuit board and the placement of components play a key role, which directly affects the installation, reliability, ventilation and heat dissipation of the entire printed circuit board, and wiring the through rate.
After the position and shape of the components on the PCB are determined, consider the wiring of the PCB
Second, in order to make the designed product work better and more effectively, the PCB has to consider its anti-interference ability in the design, and it has a close relationship with the specific circuit.
3. After the components and circuit design of the circuit board are completed, its process design should be considered next. The purpose is to eliminate all kinds of bad factors before the production starts, and at the same time, the manufacturability of the circuit board must be taken into account in order to produce high-quality products. and mass production.
When talking about the positioning and wiring of components, we have already involved some of the process of the circuit board. The process design of the circuit board is mainly to organically assemble the circuit board and components we designed through the SMT production line, so as to achieve good electrical connection. To achieve the position and layout of our designed products. Pad design, wiring and anti-interference, etc., we must also consider whether the board we design is easy to produce, whether it can be assembled with modern assembly technology-SMT technology, and at the same time, it must be achieved in production. Let the conditions for producing defective products produce the design height. Specifically, there are the following aspects:
1: Different SMT production lines have different production conditions, but in terms of the size of the PCB, the size of the pcb single board is not less than 200*150mm. If the long side is too small, you can use imposition, and the ratio of length to width is 3:2 or 4:3 When the size of the circuit board is greater than 200×150mm, the mechanical strength of the circuit board should be considered.
2: When the size of the circuit board is too small, it is difficult for the whole SMT line production process, and it is not easy to produce in batches. The boards are combined together to form a whole board suitable for mass production, and the size of the whole board should be suitable for the size of the pasteable range.
3: In order to adapt to the placement of the production line, a 3-5mm range should be left on the veneer without any components, and a 3-8mm process edge should be left on the panel. There are three types of connection between the process edge and the PCB: A without overlapping edges, There is a separation groove, B has a side, and there is a separation groove, C has a side, no separation groove. There is a blanking process. According to the shape of the PCB board, there are different forms of jigsaw. For PCB The positioning method of the process side is different according to different models. Some have positioning holes on the process side. The diameter of the hole is 4-5 cm. Relatively speaking, the positioning accuracy is higher than that of the side, so there are positioning holes for positioning. When the model is processing PCB, it must be equipped with positioning holes, and the hole design must be standard, so as not to cause inconvenience to production.
4: In order to better locate and achieve higher mounting accuracy, it is necessary to set a reference point for the PCB. Whether there is a reference point and whether it is good or not will directly affect the mass production of the SMT production line. The shape of the reference point can be square , circular, triangular, etc. And the diameter is within the range of about 1-2mm, and it should be within the range of 3-5mm around the reference point, without any components and leads. At the same time, the reference point should be smooth and flat without any Pollution. The design of the reference point should not be too close to the edge of the board, and there should be a distance of 3-5mm.
5: From the perspective of the overall production process, the shape of the board is preferably pitch-shaped, especially for wave soldering. The use of rectangles is convenient for transmission. If there is a missing slot on the PCB board, the missing slot should be filled in the form of a process edge. For a single The SMT board allows missing slots. But the missing slots are not easy to be too large and should be less than 1/3 of the length of the side.
In short, the occurrence of defective products is possible in every link, but as far as the PCB board design is concerned, it should be considered from various aspects, so that it can not only realize the purpose of our design of the product, but also be suitable for the SMT production line in production. Mass production, try our best to design high-quality PCB boards, and minimize the probability of defective products.
Post time: Apr-10-2023