It is recommended that beginners compare the following basic principles one by one while wiring. After the wiring is complete, check it again with this rule.
1: The schematic diagram is based on the principle of convenient wiring and troubleshooting, reasonable use of the bus, and the use of real pin distribution.
2: Before generating the PCB, the packages of all unfamiliar devices should be made manually, and the triode packages should be made in advance.
3: A manual sketch should be performed before wiring, and a rough layout should be made under the principle of performance priority.
4: The wiring should not be parallel to the axis of the component, carefully set the ground wire, and use full or grid copper pouring appropriately.
5: The ground wires in the digital circuit should form a network, the signal clock wires should use snake-like wires reasonably, and the pads should be appropriate.
6: Manual wiring should be wired according to the network or components, and then the docking and arrangement between the blocks.
7: When editing the layout in an emergency, you must be calm. Generally, you only need to change individual components or one or two networks.
8: When making the PCB, leave at least five soldering holes, four corners and the center in the blank space for hole alignment.
9: It is best to brush tin before soldering. The components are placed on the board first, fixed with tape and then soldered.
10: The wiring of the ADC circuit should be separated from the wiring of other digital circuits or signal lines (especially clocks), and parallel and crossing are strictly prohibited.
11: The oscillating crystal should be as short as possible and surrounded by ground wires, but be careful not to increase the load capacitance due to too small spacing.
12: There must be at least 50% metal layers for single and double panels, and at least four layers of metal layers for multi-layer panels to prevent local overheating and fire.
13: The signal wires should be as thick and short as possible. Ground wires should be added between signal wires and input and output wires, and ground wires should also be clamped between modules.
14: When the device pins are in contact with the ground wire, it is better not to use a large area of copper, but to use a grid. The entire board is also covered with a grid to prevent peeling.
15: If there is a large area of copper pouring on the PCB, a few small openings smaller than 3.5mm should be opened on the ground, which is equivalent to a grid.
16: When jumpers are used to avoid excessively long wiring, the jumpers should not be placed under large devices such as IC integrated blocks to facilitate plugging and unplugging.
17: When laying out and wiring, the heat dissipation and ventilation of the device should be fully considered. The heat source should be close to the edge of the board, and the distance between the test points should be designed.
18: In the multi-layer anti-electromagnetic interference design, the 20H rule and the 3W rule should be applied to overcome boundary radiation coupling and logic current magnetic flux interference.
19: It is best not to have the same current direction for the dual signal lines, and to control the minimum parallel length, such as using JOG routing or sine and cosine routing.
20: The interference caused by the upper and lower edge changes of the signal in the low-frequency line is much greater than the interference caused by the frequency, so we should also pay attention to the crosstalk problem.
21: The high-speed signal line should be properly terminated and matched, and it is best to keep its impedance unchanged during transmission, and widen the width of the line as much as possible.
22: Don't forget to add filtering and coupling capacitors between the power supply and ground of the integrated block to eliminate interference.
With the increasing density of modern integrated devices, the quality of PCB layout directly affects the performance of the product, and is even the key to the success of the design. As an electronics expert said: Ten kinds of devices may also have countless arrangements. But if there is a little error, its performance may be a hundred times different!
This article is reproduced from: Electronic Engineering Network
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