ding connector should be considered to facilitate the power plug;
9. The layout of other components
All the IC components are aligned side by side; the polarity of the components should be marked clearly but shouldn’t be in more than two directions in the same printed circuit board, or the directions need to be perpendicular to each other;
10. The board wiring should be well-balanced and should be filled with mesh copper when the density difference is too large, and the gridding is more than 8mil (or 0.2mm);
11. The pad cannot have through-hole to avoid the poor solder paste in components. Important signal lines are not allowed to pass through the socket feet;
12. Pay attention to patch unilateral alignment and the character direction and packaging direction should be consistent;
13. The polarity mark of the device in the same board should be as much as possible consistent.
The component wiring rules
1. The distance from the wiring area to the PCB board edge cannot exceed 1mm, and the wiring is prohibited 1mm around installation hole
2. The power wire should be as wide as possible and not be less than 18mil; signal line width should not be less than 12mil; cpu input the output line should not be less than 10mil (or 8mil); line spacing is not less than 10mil;
3. The normal through-hole is not less than 30mil;
4, Dual in-line: pad 60mil, aperture 40mil;
1 / 4W resistance: 51 * 55mil (0805 surface); pad 62mil, aperture 42mil;
Promise capacitance: 51 * 55mil (0805 surface); pad 50mil, aperture 28mil;
5. The power and ground wire should be as radial as possible, and the signal line can not appear loop alignment.
How to improve the anti-jamming capability and electromagnetic compatibility when developing electronic products with processor?
1. the following systems should be paid special attention to anti-electromagnetic interference:
(1) Microcontrollers with particularly high clock frequency and fast bus cycles.
(2) System contains high-power and high current drive circuit, such as the spark production relay, high current switch, etc.
(3) System with weak analog signal circuit and high precision A / D conversion circuit.
2. Measures for increasing the system's anti-electromagnetic interference ability:
Use low frequency microcontrollers
Low external clock frequency microcontrollers can effectively reduce noise and improve the system's anti-jamming capability. The same frequency of square wave and sine wave, square wave in the high-frequency components are much more than the sine wave. Although the wave amplitude of the high frequency component of square wave is smaller than that of the fundamental wave, the higher frequency is easier to emit as a noise source and the most influential high frequency noise generated by the microcontroller is about as three times as the clock frequency.
Reduce the distortion in signal transmission
Microcontrollers are mainly manufactured by high-speed CMOS technology. In the signal input side, the static input current is about 1mA, the input capacitance is roughly 10PF. With high input impedance, high-speed CMOS circuit output has a considerable load capacity, that is a considerable output value. The door output is lead to a very high input impedance input through a very Long line, causing serious reflection problem which will result in signal distortion and increasing system noise. When Tpd>>Tr, a transmission line problem comes into being, so you must consider signal reflection, impedance matching and other issues.
The delay time of signal on the printed circuit board is related to the characteristic impedance of the lead, namely, it is connected with the dielectric constant of the PCB material. It can be roughly assumed that the transmission speed of the signal in the printed circuit board is about 1/3 to 1/2 of the light speed. The Tr (standard delay time) of the commonly used logical telephone elements in the system constituted by the microcontrollers is between 3 and 18 ns.
On the printed circuit board, the signal passes through a 7W resistor and a 25cm long lead and the line delay time is