Designing a circuit as an electronic engineer is a must-have hard work, but the principle design is perfect. If the board design is unreasonable, the performance will be greatly reduced, and even if it is serious, it will not work properly. Based on my experience, I have summarized the following points in the PCB design, I hope to give you some inspiration.
Regardless of the software used, PCB design has a rough program that saves time and effort in order, so I will introduce it according to the production process. (Because the protel interface style is close to the windows window, the operating habits are similar, and there are powerful simulation functions, more people use, this software will be explained.)
Schematic design is a preliminary preparation work. It is often seen that beginners can draw PCB boards directly in order to save trouble. This will not pay off. For simple boards, if you are skilled in the process, you may wish to skip. But for beginners, you must follow the process. On the one hand, you can develop good habits. On the other hand, you can only avoid complicated circuits.
When drawing the schematic diagram, the hierarchical design should pay attention to the fact that each file is connected as a whole at the end, which is also important for future work. Because of the difference in software, some software will appear to be connected to the actual unconnected (electrical performance). If you don't use the relevant detection tool to detect it, if something goes wrong, it will be late if the board is ready. Therefore, the importance of doing it in order is emphasized again and again, and I hope to draw everyone’s attention.
The schematic is based on the design project, as long as the electrical connection is correct, nothing to say. Below we focus on the issues in the specific board making process.
1. Making a physical borderThe closed physical frame is a basic platform for the future component layout and routing, and also plays a role in the automatic layout. Otherwise, the components coming from the schematic will be overwhelmed. But be sure to pay attention to the accuracy here, otherwise the trouble of installing problems in the future can be big. There is also the use of arcs in the corners, on the one hand to avoid sharp corners of the workers, but also to reduce the stress. In the past, one of my products always had a case where the PCB of the face shell broke in some machines during transportation. It would be nice to use the arc.
2. Introduction of components and networksThe frame that draws the components and the network should be very simple, but there are often problems here. Be sure to carefully follow the mistakes of the prompts, and it will take more effort. The problems here generally have the following:
The package form of the component can't be found, the component network problem, there are unused components or pins, and these problems can be quickly fixed.
3. Component layoutThe layout of the components and the traces have a great influence on the life, stability and electromagnetic compatibility of the products, and should be paid special attention. Generally speaking, there should be some principles as follows:
(1) Placement order
First place the components in the fixed position related to the structure, such as power sockets, indicators, switches, connectors, etc. After these devices are placed, they are locked by the LOCK function of the software so that they will not be moved in the future. Then place special components on the line and large components, such as heating components, transformers, ICs, etc. Finally place the small device.
(2) pay attention to heat dissipation
The component layout must pay special attention to the heat dissipation problem. For high-power circuits, those heating elements, such as power tubes and transformers, should be placed as far as possible in a distributed layout to facilitate heat dissipation. Do not concentrate in one place or high capacitance so as to avoid premature aging of the electrolyte.
4. wiringWiring principle
The learning of the line is very advanced, everyone will have their own experience, but there are still some general principles.
â—†High-frequency digital circuit is thinner and shorter.
â—† High current signal, high voltage signal and small signal should be separated from each other (the isolation distance is related to the withstand voltage to be withstand. Usually, the distance is 2mm on the board at 2KV, and the ratio is increased above this. For example, if you want to withstand the withstand voltage test of 3KV, the distance between the high and low voltage lines should be more than 3.5mm. In many cases, to avoid creepage, the slot between the high and low voltage on the printed circuit board is also required.)
â—†When two panels are wired, the conductors on both sides should be perpendicular, oblique, or curved, avoiding parallel to each other to reduce parasitic coupling. The printed conductors for the input and output of the circuit should be parallel to the rabbits. In order to avoid feedback, it is best to add a grounding wire between these wires.
â—†The corner of the line should be as large as 90 degrees, the corner below 90 degrees should be eliminated, and the corner of 90 degrees should be used as little as possible.
â—† Same as address line or data line, the difference of the length of the trace should not be too large, otherwise the short-term part should be compensated for the bend line.
â—†The trace should be as far as possible on the soldering surface, especially the PCB of the through hole process.
â—†Use fewer vias and jumpers as much as possible
â—†The single-panel pad must be large, the line connecting the pad must be thick, and the teardrop can be placed on the teardrop. The quality of the general single-panel manufacturer will not be very good, otherwise there will be problems with soldering and RE-WORK.
â—†Large-area copper should be meshed to prevent bubbles from forming on the board during wave soldering and bending due to thermal stress. However, in special occasions, the flow direction and size of GND should be considered. It cannot be simply filled with copper foil. But need to go to the line
â—† Components and traces should not be placed too far on the side. Generally, the single panel is mostly a paper board. It is easy to break after being stressed. If it is connected at the edge or the components will be affected.
â—† must consider the convenience of production, commissioning and maintenance
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