PCB layout techniques

- Aug 10, 2016-

1, the input and output terminal adjacent parallel edges should be avoided to avoid reflection interference. If necessary add ground isolation, two wiring layers adjacent to each other vertically, parallel prone to parasitic coupling.


2, power supply, coupled between ground decoupling capacitor. Try to widen the power, ground width, it is better than the power ground line width, their relationship is: Ground> power cables> signal lines, generally signal line width: 0.2 ~ 0.3mm, the width by a fine of up to 0.05 ~ 0.07mm, the power cord is 1.2 ~ 2.5mm


3 of handling digital circuits and analog circuits, high-frequency digital circuits, analog circuits strong sensitivity of the signal line, the high-frequency signal lines as far away from the sensitive analog circuit devices, to ground it entire PCB to the outside world is only one node, it must be processed in the PCB inside the mold problem common ground, and in the board internal digital and analog ground are physically separate unconnected between them, with only PCB interface connected to the outside world (such as plugs, etc.). Digital and analog ground a little short, please note that only one connection point. There are no common ground on the PCB, which is determined by the system design.


4, as far as possible to shorten the connection between the high-frequency components, try to reduce electromagnetic interference parameters and their distribution between each other. Susceptible to interference components can not suffer too close to each other, the input and output components should be kept away. There may be a higher potential difference between certain components or wires, should increase the distance between them, in order to avoid accidental discharge leads to a short circuit. With high voltage components should be arranged at the time of commissioning the reach of the hand.


5, the circuit in the high-frequency operation, to consider the distribution parameter between components. General circuit components should as far as possible parallel. Thus, not only beautiful. And easy assembly and welding. Easy to mass production.


6, with the input and output ends of the wires should be avoided adjacent parallel. Plus the best line between the ground, in order to avoid feedback coupling.


7, printed conductors and generally arc-shaped corner, and right-angle or angle in high-frequency circuits can affect electrical performance. Have to take as a right angle, generally use two 135-degree angle instead of rectangular.

8, the power line design


Depending on the size of the current printed circuit board, try to rent the power line width, reduce loop resistance. At the same time, the power line in the same direction toward the ground, and data transmission, which helps to enhance noise immunity.

9, ground design


Ground design principles are:


(1) digital and analog ground separately. If both the logic circuit on the circuit board there are linear circuits, they should be separated as much as possible. Low frequency circuit ground should be used in parallel to a single point grounding, the actual wiring difficult part series and then parallel to the ground. High-frequency circuits should adopt multi-point tandem grounded, ground rent should be short and surrounded by high-frequency components as much as possible with a grid-like large area foil.


(2) ground should be bold. If the ground line is sewing lines, the ground potential changes with the current changes, so anti-noise performance. Therefore, the ground wire should be bold, it allows current to pass three times on the PCB. If possible, the ground wire should be 2 ~ 3mm or more.


(3) grounding wire closed loop path. PCB only by a digital circuit, the grounding circuit loop cloth into the group most able to improve noise immunity.

10. A decoupling capacitor configuration


One conventional approach PCB design is in key parts of the PCB to configure the appropriate decoupling capacitors.


Decoupling capacitors general configuration principles are:


(1) power input jumper 10 ~ 100uf the electrolytic capacitor. If possible, take better 100uF or more.


(2) In principle, each integrated circuit chip should be arranged in a 0.01pF ceramic capacitor, in case of PCB gap is not enough, every 4 to 8 chip arrangement but a 1 ~ 10pF capacitance.


(3) For noise immunity is weak, shut off the power when the variation in devices, such as RAM, ROM memory device should be between the chip power and ground direct access to the decoupling capacitors.


(4) capacitor lead not too long, especially in the high-frequency bypass capacitor can not have a lead.

11, should also pay attention to the following points:


(1) There are contacts, relays, buttons and other elements when the PCB. They will produce a larger spark discharge during operation, it must be shown in the drawings RC circuit to absorb the discharge current. R generally take 1 ~ 2K, C takes 2.2 ~ 47UF.


(2) CMOS input impedance is high, and vulnerable to induction, so when you want to end without the use of ground or positive supply


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