PCB design method and key points analysis

Basic requirements for PCB board design


Printed circuit board design, start from the size of the board, the size of a printed circuit board by the chassis shell size limit, to just ANN into the shell is appropriate, then, should consider the connection of printed circuit boards and external components. Printed circuit boards and external components are usually connected by plastic wires or metal insulated wires. But sometimes it is also designed as socket form. A plug-in printed circuit board is installed inside the device to provide a contact position for the socket. For larger components mounted on the printed circuit board, metal fittings shall be attached to improve vibration resistance and impact resistance.


The basic method of wiring diagram design


We need to select components and various socket specifications, size, area and have a complete understanding of the position of each component; arrange the reasonable and careful consideration, mainly from the angle of electromagnetic compatibility, anti-interference, short line, cross, power supply, the path and decoupling etc. consider. After the location of each component is determined, each component is connected on-line. According to the circuit diagram to connect the relevant pins, there are many ways to complete, and the design of the printed circuit diagram has two kinds of computer aided design and manual design methods.


Then, determine the required printed circuit board size, and according to the principle diagram, the location of the various components tentatively identified, then continue to adjust the layout more reasonable, the printed circuit board wiring between various components of the arrangement are as follows:


Cross circuit is not allowed in printed circuit, and two lines can be solved by "drilling" and "winding". That is, let a lead from other resistors, capacitors, transistors at the foot of the gap at the "drill" in the past, or from the end of may lead a cross around "in the past, in the special case of how the circuit is very complicated, in order to simplify the design also allows the use of wire jumper, solve the problem of cross circuit.


Resistors, diodes, tubular capacitors and other components have "vertical", "horizontal" two installation methods. Refers to the vertical component body perpendicular to the circuit board installation and welding, the utility model has the advantages of saving space, refers to the horizontal component body parallel and close to the circuit board installation, welding, the utility model has the advantages of good mechanical strength components installed. These two different mounting components, the printed circuit board components, the hole spacing is not the same.


Take place at the same level circuit should be as close as possible, and the circuit of the powersupply filter capacitor will be in the class to access locations. In particular the leveltransistor base emitter access locations not too far away, or due to the two grounding points between the copper foil is too long will cause interference with the self, the "one point grounding method of circuit, work is stable, not easy to self.


The general principles of the arrangement of wire must be in strict accordance with the high - frequency - at a low level and weak to strong power order, must not casually and chaos, between stages can be rather long connection point, must comply with this provision. In particular, the frequency converter, regeneration head, FM head of the ground wire arrangement requirements more stringent, if there is improper, it will produce self-excited, and can not work.


A large area enclosed ground wire is often used in FM first class high frequency circuits, so as to ensure good shielding.


The high current lead (common ground wire, power amplifier, lead wire, etc.) shall be as wide as possible to reduce the wiring resistance and its voltage drop, and to reduce the self excitation due to parasitic coupling.


The line with high impedance is as short as possible, and the line with low impedance is longer, because the wire with high impedance is easy to generate the flute and absorb the signal, which causes the circuit to be unstable. Power line, ground wire, no base feedback assembly line, emitter lead are low impedance line, ground base emitter follower line, the two channel recorder to be separated, each way, until the end of efficacy and together, such as two ground wires to connect to the pole, easy to produce crosstalk, the separation degree decreased.


 

(Source: internal information)

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