When beginners draw PCB, they should compare the above basic principles one by one while wiring. After wiring is completed, they should check this rule again. Over time, it will work. The ancients said, “It’s hard to walk.” After all, there are few talented people in the world. Only by persevering can we achieve results. The word “gradually” implies the truth that almost everything is mature.
In addition, don’t forget to add filters and coupling capacitors between the power supply of the integrated block and the ground to eliminate interference.
Explain another misunderstanding of PCB wiring: some friends who only want to be quick, some friends who don’t really want to work hard on technology, and some friends who want to be opportunistic always think that after learning some board-making software such as Protel/DXP, they will be able to make PCB, so they can decorate the window. And I said: Brother, don’t be so naive. Technology, there is no shortcut! Maybe you are smarter, but you must go through enough learning and practice. Otherwise, what you do is nothing but “beautiful”! Being pragmatic is the duty of being a man and waiting for things, and it is also the minimum criterion for engineering.
Look at a board: Don’t laugh at others for having more jumpers!
Look at a board: don’t laugh at others’ hesitation and pains!
If you smile, first of all, it means that you are not in place, secondly, your knowledge is superficial, and thirdly, your skills are poor.
If you are a man, you can see your skill in your heart, and the subtleties show your spirit! Don’t show off, just seek truth!
[Rule ]1: The schematic diagram is based on the principle of convenient wiring and troubleshooting. The bus should be used reasonably, and the real pin distribution should be used.
[Rule ]2: Before PCB is generated, all unfamiliar devices should be packaged by hand, and triode packages should be made in advance.
[Rule ]3: Before wiring, a manual sketch should be done, and the general layout should be made under the principle of performance first.
[Rule ]4: The wiring should not be parallel to the axis of components, the ground wire should be carefully set, and comprehensive or grid copper-clad should be used appropriately.
[Rule ]5: In digital circuits, the ground wire should be netted, the signal clock wire should use the snake wire reasonably, and the pad should be appropriate.
[Rule ]6: Manual wiring should be based on the network or components, and then the docking and arrangement between the blocks should be carried out.
[Rule ]7: When the layout is modified in an emergency, you must be calm. Generally, you only need to change individual components or one or two networks.
[Rule ]8: When making PCB, at least five solder holes, four corners and the center should be left in the blank space for hole alignment.
[Rule ]9: Before welding, it’s best to brush the tin, put the components on the board first, and fix them with adhesive tape before welding.
[Rule] 10: The ADC circuit wiring should be separated from the wiring of other digital circuits or signal lines (especially clocks), and it is forbidden to run parallel and cross.
[Rule ]11: Oscillating crystal should be as short as possible and surrounded by ground wire, but be careful not to increase the load capacitance due to too small spacing.
[Rule ]12: Single and double panels should have at least 50% metal layers, and multi-layer panels should have at least four metal layers to prevent local overheating and fire.
[Rule ]13: The signal lines should be as short as possible with the same thickness. Ground wires should be added between the signal lines and the input and output lines, and ground wires should be clamped between modules.
[Rule ]14: It’s best to use a grid instead of a large area of copper coating when the device pins are in contact with the ground wire. Grid is also used for the whole board copper coating to prevent peeling.
[Rule ]15: If there is a large area of copper clad on the PCB, several small holes should be made on the ground, but the holes should not be larger than 3.5mm, which is equivalent to a grid.
[Rule ]16: When jumper wires are used to avoid too long wiring, the jumper wires should not be placed under large devices such as IC integrated blocks to facilitate plugging and unplugging.
[Rule ]17: Heat dissipation and ventilation of devices should be fully considered in layout and wiring. The heat source should be close to the board edge, and the spacing of test points should be designed.
[Rule ]18: 20H rule and 3W rule should be applied in multilayer anti-electromagnetic interference design to overcome boundary radiation coupling and logical current magnetic flux interference.
[Rule ]19: It’s best not to have double signal lines in the same current direction, and to control the minimum parallel length, such as JOG wiring or sine and cosine wiring.
[Rule ]20: The interference caused by the fluctuation of the signal in the low-frequency line is far greater than that caused by the frequency, so we should also pay attention to the crosstalk problem.
[Rule ]21: High-speed signal lines should be added with appropriate termination matching, and it is best to keep their impedance unchanged during transmission, and try to widen the width of the lines.
[Rule ]22: Don’t think that PCB making is very simple, it only shows that your level needs to be improved. With the increasing density of modern integrated devices, the quality of PCB layout directly affects the performance of products, even the key to the success or failure of design. As a Japanese electronics expert said: Ten kinds of devices may also have countless possible arrangements. But if there is a little error, its performance may be 100 times apart! The importance and technology of PCB layout can be seen. Today, I encountered some problems when I made the board, which caused the PCB I drew to show no competitiveness!
When drilling holes for the board, because the original only made a single panel and rarely used the method of leaving blank on one side, there were some unexpected situations when making a double-sided board with blank edge.Almost lead to the abandonment of previous achievements and mental depression.
Now the lessons are summarized as follows: when exporting PCB solder hole and via hole data files, the layout printed by CNC machine tool is reverse to the layout displayed in the computer, or is mirrored.That is: the actual board is the layout after turning 180 degrees to the right with the right edge line as the reference line in the circuit diagram.Special attention should be paid when there is a blank!Otherwise, the board will be useless!
When making a single panel, you can use the method of three or five points to insert the holes in the board. You can also transfer the ink paper to the copper clad laminate, and then use the method of 0, 0 points or adding a diagonal line to make the NC machine automatically locate and punch holes on it.However, due to the naked eye to the reference coordinate point, a slight error may lead to all holes not accurate.Be careful and patient about it!