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1. The PCB board design starts from the size of the circuit board. The size of the PCB board design is limited by the size of the shell, so it can be placed in the shell. Secondly, the PCB board design and external components should be considered. (Mainly potentiometer, socket or other PCB board design) connection. The PCB board design and external components are usually connected by plastic wires or metal isolation wires. But sometimes they are also designed as sockets. That is: a plug-in printed circuit board installed in the equipment should have a contact position that acts as a socket. For larger components mounted on printed circuit boards, metal parts must be connected to improve vibration and shock resistance.
2. The basic method of wiring diagram design first needs to fully understand the specifications, sizes and areas of the selected components and various sockets; reasonably and carefully consider the location of each component, mainly from electromagnetic field compatibility, anti-interference angle, and short wiring. Less crossover, power supply, ground path and decoupling, etc. After determining the position of each component, it is the connection of each component, and the related pins are connected according to the circuit diagram. There are many kinds of printed circuit diagrams. There are two methods of computer-aided design and manual design. The most primitive is to arrange the layout manually. This is more complicated and often needs to be repeated several times before completion. This is when there is no other drawing equipment. This manual arrangement method may also be very helpful to designers who have just studied printing plates. Computer-aided graphics, now there are various drawing software with different functions, but generally speaking, drawing and modification are more convenient, and can be saved and stored.
Next, determine the required printed circuit board size, and determine the location of each component according to the schematic diagram, and then make adjustments to make the layout more reasonable. The wiring layout between PCB components is as follows:
(1) Cross circuits are not allowed in printed circuits. For possible crossover lines, it can be solved by "drilling" or "winding". In other words, let a certain lead come out from the gap under the pins of other resistors, capacitors and transistors. In the past, drilling holes, or "winding" from one end of the lead that may cross, how to complicate the circuit under special circumstances and allow the use of jumpers to simplify the design to solve the cross circuit problem.
(2) Resistors, diodes, tubular capacitors and other components can be installed in two ways: "vertical" and "horizontal". Vertical refers to the installation and soldering of the component body perpendicular to the circuit board, which has the advantage of saving space, and horizontal refers to the installation and soldering of the component body in parallel and close to the circuit board. The advantage is that the mechanical strength of the component installation is better. Two different mounting components have different hole spacing on the printed circuit board.
(3) The grounding point of the circuit of the same level should be as close as possible, and the power filter capacitor of the current level circuit should also be connected to the grounding point of the level. In particular, the grounding point of the base and emitter of the transistor of this level should not be too far away. Otherwise, because the copper foil between the two grounding points is too long, it will cause interference and self-excitation. The circuit using this "single point grounding method" is stable and not easy to self-excite.
(4) The total ground wire must strictly follow the high-frequency intermediate frequency and low-frequency first-order principle in the order of weak current to strong power. It must not be turned over. Levels and stages are better connected and long-term. This rule. In particular, the grounding wire arrangement requirements of the inverter head, regeneration head and FM head are more stringent. If it is not suitable, it will be self-motivated and unable to work. High-frequency circuits such as FM heads usually use large-area enclosed ground wires to ensure good shielding.
(5) High current leads (common ground, power amplifier power leads, etc.) should be as wide as possible to reduce wiring resistance and voltage drop, and reduce self-excitation caused by parasitic coupling.
(6) High-impedance traces should be as short as possible, and low-impedance traces may be longer, because high-impedance traces are prone to ripple and absorb signals, resulting in circuit instability. The base, ground, non-feedback component trace and emitter lead of the power line are all low-impedance traces. The base track of the emitter follower and the ground of the two channels of the recorder must be separated, and each channel forms a way until the end of the function, such as bidirectional grounding. When connecting lines, it is easy to produce crosstalk, thereby reducing separation.
3. The following points should be paid attention to in the design of PCB board
1. Wiring direction: starting from the welding surface, the layout direction of the components should be as consistent as possible with the schematic diagram. The wiring direction preferably coincides with the wiring direction of the circuit diagram. It is often necessary to perform various parameters on the welding surface during the production process. Therefore, it is convenient for inspection, debugging and overhaul in production (note: under the premise of meeting the circuit performance and the installation requirements of the whole machine and the panel layout).
2. Arrange the components, the distribution should be reasonable and even, and strive to be clean, beautiful, and rigorous process requirements.
3. Resistor and diode placement: There are two types: plane and vertical:
(1) Flat release: When the number of circuit components is small and the size of the circuit board is large, it is usually flat. If the resistance is lower than 14W, the distance between the two pads is usually 410 inches, when the 12W resistor is placed flat, the distance between the two pads is usually 510 inches; when the diode is placed flat, the 1N400X series Rectifiers generally use 310 inches; 1N540X series rectifiers are generally 4 to 510 inches.
(2) Vertical: When the number of circuit components is large and the size of the circuit board is not large, it is generally vertical, and the distance between two pads is generally 1 to 210 inches.
4. Potentiometer: the principle of placing the IC holder
(1) Potentiometer: It is used to adjust the output voltage of the regulator, so the design potentiometer should be fully clockwise when the output voltage rises, and the counterclockwise regulator will reduce the output voltage; the potentiometer is used in the adjustable constant current charger Adjust the charging current folding size. When designing the potentiometer, the current should be increased when the potentiometer is adjusted clockwise. The potentiometer should be placed in the overall structure and panel layout requirements, so it should be as much as possible. At the edge of the board, the handle is turned outward.
(2) IC holder: When designing a printed circuit board diagram, when using an IC holder, you need to pay special attention to whether the orientation of the positioning slot on the IC holder is correct, and pay attention to whether the IC pins are correct, for example, the first The foot can only be located at the lower right or upper left corner of the IC holder and close to the positioning groove (from the soldering surface).
5. Arrangements for entering and leaving the terminal
(1) The related two lead ends should not be too large, generally about 2 to 310 inches.
(2) The entrance and exit should be concentrated on the 1 to 2 side as much as possible, and should not be too discrete.
6. When designing the wiring diagram, pay attention to the order of the pins and the spacing of the components should be reasonable.
7. Under the premise of ensuring the performance requirements of the circuit, the design should be reasonable, the external wiring should be used less, and the wires should be wired as required. It is intuitive, easy to install, height and overhaul.
8. When designing the wiring diagram, minimize the wiring and try to make the lines simple and clear.
9. The width of the terminal strip and the line spacing should be moderate. The spacing between the two pads of the capacitor should be as close as possible to the spacing of the capacitor leads.
10. The design should be carried out in a certain order, for example, from left to right, from top to bottom.
In short, if the PCB factory follows the basic principles of PCB design, the production quality will be a qualitative leap.
