1. Make physical borders
The closed physical border is a basic platform for future component layout and routing, and also plays a role in the automatic layout. Otherwise, the components from the schematic diagram Will be overwhelmed. But here must pay attention to accuracy, otherwise the trouble of installation 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 shell PCB was broken during the transportation process, and it was better to use the arc.
2, the introduction of components and networks
It should be simple to draw the components and network into the frame, but there are often problems here, so be careful The error of the prompt is solved one by one, and it will take more effort to not face it. The problems here are generally the following:
The package form of the component cannot be found, the component network problem, there are unused components or Pins, contrast tips, these problems can be quickly resolved.
3, component layout
component layout and routing for product life, stability, electromagnetic compatibility Great influence is a place that should be paid special attention. Generally speaking, there should be some principles:
(1) Placement order
Place the fixed position element related to the structure first. Devices, such as power sockets, indicators, switches, connectors, etc., are placed and locked with the software's LOCK function so that they are not accidentally moved later. Place special components and large elements on the line. Devices such as heating elements, transformers, ICs, etc. Finally placed small Pieces.
(2) Pay attention to heat dissipation
Component layout should pay special attention to heat dissipation. For high-power circuits, those heating elements such as power tubes, transformers, etc. should be placed as far as possible in a distributed layout to facilitate heat dissipation. Do not concentrate in one place, and do not place high capacitance too close to avoid premature aging of the electrolyte.
The learning of the line is very advanced, and everyone will have their own experience.
It is very important to deal with the ground circuit for analog circuits. 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, the extremely 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 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 you can take this component away, the amplifier and AD also It is stable.
In addition,Electromagnetic compatibility issues are 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, the crystal casing is grounded, the interference signal is shielded, and special filter circuits and devices are used.
Need to specify the serpentine routing, because the application is different, the role is different, in the motherboard of the computer used in some clock signals, such as PCIClk, AGP-Clk, it has Two points: 1, impedance matching 2, filter inductance.
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, the serpentine trace 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 inductance coil of the radio antenna, etc. Wait.
5, adjust and improve
After completing the wiring, 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 It affects the speed and brings trouble to the wiring. It is also for the convenience of production, debugging and maintenance.
Copper application usually refers to the blank area left after the wiring is filled with a large area of copper foil. It can be GND copper foil or VCC copper foil (but this can easily burn the device once it is short-circuited). It is best to ground, unless it has to be used to increase the conduction area of the power supply to withstand large currents before connecting to VCC. The package usually refers to the use of two ground wires (TRAC) to wrap a signal line with special requirements to prevent it from being disturbed or disturbed by others.
If you use copper instead of ground wire, you must pay attention to whether the whole ground is connected, current size, flow direction and whether there are special requirements to ensure that unnecessary errors are reduced.
6. Check the check network
Sometimes the network relationship between the board and the schematic is different due to misoperation or negligence. At this time, it is necessary to check and check. Therefore, after painting, you must not rush to the plate-making factory.You should check first and then follow up.
7. Using the emulation function
After completing these tasks, software emulation can be performed if time permits. Especially high-frequency digital circuits, so that some problems can be found in advance, greatly reducing the amount of debugging work in the future.