A printed circuit board (PCB) is an electronic circuit support elements and devices. It provides electrical connection between the circuit elements and devices. With the rapid development of technology in electrical, PCB density is increasing. PCB design quality great influence on the anti-jamming capability. Thus, during the PCB design. PCB design must comply with the general principles of, and shall comply with anti-jamming design. To get the best performance electronic circuit, and the layout of conductor laid components is very important. In order to design good quality. Low cost PCB. Should follow the following general principles:
1. layout
First, considering the size of the PCB to PCB Colonel oversized printing line length, the impedance to increase, decrease noise immunity, the cost increases; too small, the heat is not good, and adjacent lines susceptible to interference. After determining the size of the PCB. And then determine the location of specific components. Finally, the functional units of the circuit, all the components of the circuit layout.
2 as short as possible connections between the high-frequency component, trying to reduce electromagnetic interference between each other and their distribution parameters. Susceptible to interference components is not so close to each other, the input and output elements should be kept away.
3. There may be some components or conductors between the high potential difference, we should increase the distance between them, so as to avoid accidental short discharge lead. Components with a high voltage should be arranged in place of debugging not easily reached.
4. components heavier than 15g. It should be a fixed support, and then welded. Those are big and heavy. Heat more components not mounted on the printed board, but should be mounted on the chassis base plate of the machine, and should consider heat. Thermosensitive element away from the heating element.
5. For potentiometer. Tunable inductor. Variable capacitor. Micro switch, the adjustable element layout should be considered the structural requirements of the machine. If adjusting the machine, should be placed above the printed circuit board to facilitate adjustment; outer if local regulator, whose position is to adjust the position of the knob on the panel of the chassis to adapt.
6. The PCB should stay out of the positioning hole and the position occupied by the fixing bracket.
The functional unit circuit. When all the components of the circuit layout, to comply with the following principles:
① the positional arrangement of the various functional units of the circuit according to the flow circuit of the signal flow to facilitate the layout, and the direction of the signal consistent as possible.
② the core element of each functional circuit as the center, around which to lay. Components should be uniform. neat. Compactly on the PCB. And shortening the lead and to minimize the connections between the various components.
③ circuit operating at a high frequency, consideration of the distribution parameter between the components. General circuit components should be arranged in parallel as much as possible. In this way, not only beautiful. And easy assembly and welding. Easy to mass production.
④ the edge of the circuit board components, from the edge of the board is generally not less than 2mm. The best shape of the circuit board is rectangular. Aspect ratio of 3: 2 to 4: 3. When the circuit board is larger than the size of 200x150mm. Suffered should consider the mechanical strength of the circuit board.
7. Wiring
principles wiring as follows:
① input wire output end adjacent parallel should be avoided. Between the ground line is preferably added, in order to avoid feedback coupling.
② printed photo conductor mainly by a minimum width of the adhesive strength between the pull wire and the insulating base and their current value flowing decision
set. When the foil thickness of 0.05mm. When 1 ~ 1.5mm in width. 2A through current, the temperature is not higher than 3 ℃, therefore. Conductor width of 1.5mm to meet the requirements. For integrated circuits, especially digital circuits, typically selected width of 0.02 ~ 0.3mm wire. Of course, by permitting, or as wide lines. In particular power and ground. The minimum spacing between the wires is mainly determined by the worst case line insulation resistance and breakdown voltage. For integrated circuits, especially digital circuits, as long as the process allows, to make small spacing 5 ~ 8mm.
④ wiring printed wiring board to note the following: zero volts dedicated lines, power lines trace widths ≥1mm; power line and ground as close as possible, the entire printing plate was shaped to power and ground distribution "well", so that the distribution of line current reaches equilibrium; to provide a zero-volt line is an analog circuit specifically; to reduce alien crosstalk, increase the distance between the print lines when necessary, care; sandwiched with zero volt line as the inter-line isolation; plug printed circuit also to arrange a number of multi-line as zero volts
Isolation between lines; special attention to the size of the current conductor loop circulation; if possible the entrance of the control line (printed board) of the RC decoupling affixed, to eliminate confounding factors that may occur in transmission; printed arc Do not linewidth mutation, do not suddenly lead corner (≥90 degrees).
⑤ pad
pad larger than the diameter of the device lead. However, the pad is too easy to form Weld. D pads generally not less than the outer diameter (d + 1.2) mm, where d is the pore diameter of the lead. High density digital circuits, the smallest diameter of the pad is desirable (d + 1.0) mm.
PCB circuit and anti-jamming measures to
interference specific circuit design and printed circuit board has a close relationship, here only in respect of several PCB anti-jamming design
commonly used measures do some explanation.
1. Design of the power line
according to the magnitude of the current printed circuit board, as far as possible rent power line width, reducing the loop resistance. Simultaneously. Power supply line and the ground line to transfer data in the same direction, which helps enhance the noise immunity.
2. Ground design
principles ground design is:
① digital and analog separately. If the circuit board both have linear logic circuits that allow them to be separated. The low frequency circuit should be single point parallel ground, partially ground in series and then in parallel the actual wiring may be difficult. Multi-point high-frequency circuit should be connected in series to ground, the ground should be short and rent, high-frequency components as much as possible around a large area with a grid-like foil.
② ground wire should be bold. If the ground line with a fine line, a ground potential changes with the current changes, so that the anti-noise performance. Ground line should therefore be thickened, so that it allows current to pass three times on the PCB. If possible, should be in the ground line 2 ~ 3mm or more.
③ ground line constituting a closed loop. PCB only composed of digital circuits, the circuit ground cloth into a closed loop to improve the noise immunity most.
3. The decoupling capacitors arranged
one PCB design is conventional practice appropriate decoupling capacitors disposed in the respective key parts PCB. Configuring general principle of decoupling capacitors is:
1. The power input terminals connected across the electrolytic capacitor 10 ~ 100uf. If possible, take more than 100uF better.
2. The integrated circuit chip on each principle should 0.01pF of a ceramic capacitor is arranged, in case of insufficient void PCB, every 4 to 8 can be arranged, but the chip capacitor is a 1 ~ 10pF.
3. weak for noise immunity. Large off power variation device, such as a memory device RAM.ROM, should be directly into the decoupling capacitance between the chip power and ground.
4. The capacitor leads can not be too long, especially in a high frequency bypass capacitor can not have a lead. In addition, the following points should be noted:
A. a contact in the printed board. Relay. Button or the like when the element. Will produce a greater spark discharge operation thereof, RC circuit shown in the drawings must be used to absorb a discharge current. R generally takes 1 ~ 2K, C takes 2.2 ~ 47UF.
B.CMOS high input impedance, and susceptible to induction, so the use of ground or not to end the positive supply.
⑦ using a logic circuit useful recommendations: who can do high-speed logic circuit do not; decoupling capacitors between the power supply and ground; Note that waveform distortion long transmission; RS flip-flop with the fit between the button and an electrical circuit for a buffer good things to share! Welcome to criticism, to testify, it is recommended!
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