Get the best performance to make the electronic circuit, the layout of the components and layout of the wire is very important. In order to design, good quality, low cost of PCB should follow the following general principles.

(1) special components layout

First of all, want to consider the size of the PCB size: PCB size is too large, the printing lines long, impedance increases, anti-noise ability, cost also increase; Is too small, the heat dissipation is not good, and the adjacent lines are susceptible to interference. In determining the size of PCB, and then determine the location of the special components. Finally, according to the function of the circuit unit, for all the components of the circuit layout.

When determining the location of the specific components to abide by the following principles:

(1) as far as possible, shorten the connection between the high frequency components, try to reduce their distribution parameters and the electromagnetic interference between each other. Vulnerable to the interference of components can't get too close to each other, should as far as possible away from the input and output components.

(2) some components or may have a higher potential difference between a conductor and should increase the distance between them, so as to avoid discharge lead to accidental short circuit. With high voltage components should be set in the debugging of the reach of hand.

(3) the weight of more than 15 g of components, ought to use fixed bracket, then welding. Those are big and heavy, calorific value more components, should not be installed on the printing plate, and should be installed on the machine chassis backplane, and heat dissipation problems should be considered. The temperature sensor should be far away from the heating element.

(4) for potentiometer, adjustable inductor, capacitor, micro switch adjustable components such as layout, the structure of the machine should be considered. If the machine adjustment, should be on the printing plate is convenient to adjust place; If it is closed to adjust, its position with the position of the adjusting knob on the chassis panel.

5. Set aside printing plate location hole and fixed bracket position occupied.

(2) general components layout

According to the function of the circuit unit, all components of circuit layout, to comply with the following principles:

(1) according to the process of the circuit arrangement of each functional circuit unit, to facilitate signal flow, layout and make the signal as much as possible to maintain consistent direction.

(2) for the center with the core of each functional circuit components, layout around it. Compact components should be uniform, neat, is arranged on the PCB, as far as possible to reduce and shorten the lead and the connection between each components.

(3) work under high frequency circuit, want to consider the distribution of components between parameters. General circuit should make components in parallel as far as possible, in this way, not only beautiful, and easy fabrication, easy to mass production.

(4) in the circuit board on the edge of the components, circuit board edge is generally not less than 2 mm. The best shape for the rectangular circuit board. Aspect ratio is 3:2 or 4:3. Circuit board face size greater than 200 mm * 150 mm, the circuit board by mechanical strength should be considered.

(3) the wiring

The wiring principle is as follows:

(1) the input and output end with adjacent parallel wires should avoid as far as possible, had better add ground between line, lest produce feedback coupling.

(2) the printing plate conductor is the smallest width of the main by the adhesion strength between the conductor and insulation substrate and through their current value decision. When the thickness of the copper foil is 0.5 mm, width is 1 ~ 15 mm, with 2 A current, temperature rise will not higher than 3 ℃. Therefore, wire width of 1.5 mm can meet the requirements. For integrated circuits, digital circuits, in particular, usually choose 0.02 ~ 0.3 mm wire width. Of course, as long as allow, or as much as possible with wide line, especially the power cord and the earth. Conductor is mainly by the shortest distance between the worst case of the insulation resistance between wire and breakdown voltage. For integrated circuits, digital circuits, in particular, as long as technology allows, can make the spacing is less than 0.1 ~ 0.2 mm.

(3) printed wire bend generally take circular arc form, and the right Angle or the Angle in the high frequency circuit can affect electrical performance. In addition, as far as possible avoid the use of large area of copper foil, otherwise, the time when heated, prone to copper foil inflation and falls off phenomenon. When must use large copper foil, it is best to grid shape, it is advantageous to the exclusion of copper foil adhesive between the substrate and volatile gas heats.

(4) bonding pad

Bonding pad center hole lead diameter larger than the device. Easy to form virtual welding welding plate is too big. Bonding pad diameter D is generally not less than (D + 1.2) mm, where D of aperture. Digital circuit of high density, bonding pad minimum desirable (d + 1.0) mm in diameter.