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. 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, you may 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. Make a physical border
The 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 surface of the PCB was broken in a certain machine during transportation. It is better to use the arc.
2. Introduction of components and networks
The 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 layout
The 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. Wiring
Wiring 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
It is very important for the analog circuit to deal with the problem. The noise generated on the ground is often inconvenient, but once it is generated, it will cause great trouble and should be satin. For the power amplifier circuit, very small ground noise will have a significant impact on the sound quality due to the amplification of the latter stage; in the high-precision A/D conversion circuit, if there is a high-frequency component on the ground line, a certain temperature drift will occur, affecting The work of the amplifier. At this time, you can add the è—• capacitor at the 4 corners of the board, one foot and the ground connection on the board, and one foot to the mounting hole (connected by the screw and the case), so that this component can be taken care of, the amplifier and AD also It is stable.
In addition, the issue of electromagnetic compatibility is even more important in the current situation of people paying more attention to environmentally friendly products. Generally speaking, there are three sources of electromagnetic signals: signal source, radiation, and transmission line. The crystal oscillator is a common high-frequency signal source. The energy value of each harmonic of the crystal oscillator on the power spectrum will be significantly higher than the average value. It is feasible to control the amplitude of the signal, ground the crystal oscillator case, shield the interference signal, and use special filter circuits and devices.
Need to specify is the serpentine routing, because the application is different, its role is different, in the computer's motherboard used in some clock signals, such as PCIClk, AGP-Clk, its role has two points: 1, impedance matching 2. Filter inductor.
For some important signals, such as HUBLink in the INTELHUB architecture, a total of 13 frequencies, up to 233MHZ, must be strictly equal in length to eliminate the hidden danger caused by time lag. At this time, serpentine routing is the only solution.
Generally speaking, the line spacing of the serpentine trace is >=2 times the line width; if it is in the ordinary PCB board, in addition to the function of the filter inductor, it can also be used as the inductor coil of the radio antenna and the like.
5. Adjust and improve
After the wiring is completed, all you have to do is make some adjustments to the text, individual components, routing, and copper (this work should not be too early, otherwise it will affect the speed and cause trouble to the wiring), also for the convenience of production, Commissioning and maintenance.
Copper application usually refers to the blank area left after filling the wiring with a large area of ​​copper foil. It can be used to lay GND copper foil or VCC copper foil (but it is better to ground the device once it is short-circuited, unless it is necessary to use it). To increase the conduction area of ​​the power supply to withstand a large current to connect to VCC). The package usually refers to two ground wires (TRAC).
Absolute rotary Encoder measure actual position by generating unique digital codes or bits (instead of pulses) that represent the encoder`s actual position. Single turn absolute encoders output codes that are repeated every full revolution and do not output data to indicate how many revolutions have been made. Multi-turn absolute encoders output a unique code for each shaft position through every rotation, up to 4096 revolutions. Unlike incremental encoders, absolute encoders will retain correct position even if power fails without homing at startup.
Absolute Encoder,Through Hollow Encoder,Absolute Encoder 13 Bit,14 Bit Optical Rotary Encoder
Jilin Lander Intelligent Technology Co., Ltd , https://www.jllandertech.com