Basic requirements for PCB diagram design
1. The design of the PCB begins with determining the size of the board. The size of the printed circuit board is large due to the size of the chassis.
The small limit is suitable for being placed in the outer casing. Secondly, the printed circuit board and external components should be considered (mainly potential).
Connections of connectors, sockets or other printed circuit boards. Printed circuit boards and external components are usually made of plastic wires or gold.
Is connected to the isolation line. But sometimes it is also designed as a socket. That is: install a plug-in printed circuit board in the device.
Leave a contact position that acts as a socket. For larger components mounted on a printed circuit board, attach a metal attachment to
Improve vibration and impact resistance.
2. Basic method of wiring diagram design
First of all, you need to have a complete understanding of the specifications, dimensions, and areas of the selected components and various sockets;
Reasonable and careful consideration of location arrangement, mainly from the perspective of electromagnetic field compatibility and anti-interference, short traces and crossover
Less, power, ground path and decoupling, etc. After the position of each component is determined, it is the connection of each component, according to the circuit
There are various ways to connect the related pins, and the design of the printed circuit diagram has computer-aided design and manual design method.
The most primitive is the manual arrangement of the layout. This is more complicated, and it often takes several times to complete the finalization.
It can also be used when drawing equipment. This manual arrangement method is also very helpful for designers who just learn to print the board.
Computer-aided drafting, there are now a variety of drawing software, different functions, but in general, drawing, modification is more convenient,
And can save and store and print.
Next, determine the required size of the printed circuit board, and determine the position of each component according to the schematic diagram,
After continuous adjustment to make the layout more reasonable, the wiring arrangement between the components in the printed circuit board is as follows:
(1) Cross circuit is not allowed in the printed circuit. For the lines that may cross, you can use “drill” and “wound”.
Solution, that is, let a lead "drill" from the gap under other resistors, capacitors, and triodes, or from a possible
One end of a crossed lead is "wound" in the past. In a special case, the circuit is very complicated. It is also allowed to simplify the design.
Line jumper to solve the cross circuit problem.
(2) Resistor, diode, tubular capacitor and other components have "vertical", "horizontal" two installation methods. Vertical refers to
The component body is mounted perpendicular to the circuit board and soldered, which has the advantage of saving space. The horizontal type means that the component body is parallel and closely attached to
Board mounting, soldering, has the advantage of better mechanical strength of component mounting. These two different mounting components, printed circuit
The hole pitch of the components on the board is different.
(3) The grounding point of the same level circuit should be as close as possible, and the power supply filter capacitor of the current stage circuit should also be connected to the stage.
At the location, especially the grounding point of the base and emitter of the transistor of this stage cannot be too far away, otherwise the copper between the two grounding points
If the foil is too long, it will cause interference and self-excitation. The circuit with such a "one-point grounding method" is more stable and less prone to self-excitation.
(4) The total ground line must be strictly in accordance with the order of high frequency-intermediate frequency-low frequency first order according to the order of weak electricity to strong electricity.
You can't just pick it up and go back and forth. Levels and stages are better to be connected longer, and you must follow this rule. Especially the inverter head, then
The grounding line arrangement of the head and the FM head is more strict. If it is improper, it will be self-excited and will not work. The FM head, etc.
High-frequency circuits often use large-area enclosed ground wires to ensure good shielding.
(5) Strong current leads (common ground, power amplifier power leads, etc.) should be as wide as possible to reduce wiring resistance and
Voltage drop can reduce self-excitation caused by parasitic coupling.
(6) The trace with high impedance should be as short as possible, and the trace with low impedance can be longer, because the trace with high impedance is easy to flute and suck.
Receiving signals, causing circuit instability. Power lines, ground lines, base traces without feedback components, emitter leads, etc. are low resistance
Anti-route, the base of the emitter follower, the ground of the two channels of the recorder must be separated, each into a way, until the work
The end of the effect is recombined. If the two ground lines are connected, it is easy to produce crosstalk, which reduces the resolution.
Third, the following points should be noted in the design of the printed board
1. Wiring direction: From the welding surface, the arrangement of the components is as close as possible to the schematic, and the wiring direction is the most
It is consistent with the direction of the circuit diagram, because it usually needs to detect various parameters on the welding surface during the production process.
To facilitate inspection, commissioning and overhaul in production (Note: before meeting the requirements of circuit performance and machine installation and panel layout requirements)
2. The arrangement of the components should be reasonable and uniform, and strive for neat, beautiful, and rigorous process requirements.
3. Resistance, diode placement: divided into two types: flat and vertical:
(1) Flat release: When the number of circuit components is small and the size of the circuit board is large, it is generally flat.
Good; for a resistor below 1/4W, the distance between the two pads is generally 4/10 inches, when the 1/2W resistor is laid flat, two
The pad spacing is generally 5/10 inches; when the diode is placed flat, the 1N400X series rectifiers are generally 3/10 inches; 1N540X
Column rectifier, generally take 4~5/10 inches.
(2) Vertical: When the number of circuit components is large and the board size is not large, it is generally vertical and vertical.
The spacing between the two pads is generally 1~2/10 inches.
4. Potentiometer: The principle of placing the IC holder
(1) Potentiometer: used to regulate the output voltage in the regulator, so the design potentiometer should be output when clockwise is full.
When the voltage rises, the output voltage of the counterclockwise regulator is reduced; in the adjustable constant current charger, the potentiometer is used to regulate the charging current.
Fold the size, when designing the potentiometer should be full clockwise adjustment, the current increases. The potentiometer should be placed in the full machine structure
Installation and panel layout requirements, so should be placed on the edge of the board as much as possible, with the handle turned outward.
(2) IC holder: When designing the printed board diagram, in the case of using the IC holder, special attention must be paid to the positioning slot on the IC holder.
Is the orientation correct, and pay attention to whether the IC pins are correct. For example, the first pin can only be located in the lower right corner of the IC holder or
Upper left corner, and close to the positioning groove (from the welding surface).
5. In and out terminal arrangement
(1) The distance between the two lead terminals is not too large, generally about 2~3/10 inches.
(2) As far as possible, the inlet and outlet ends should be concentrated on 1 to 2 sides, not 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 in the design, and the external crossover should be used less and
Compliance with the requirements of the line, and strive to be intuitive, easy to install, height and maintenance.
8. When designing the wiring diagram, keep the lines as few as possible, and try to make the lines simple and clear.
9. The width of the wiring strip and the spacing of the lines 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 in a certain order, for example, from left to right and top to bottom.