праектаванне Друкаванай платы often have such and such problems? Today I love the program network xiaobian recommended this article is engaged in PCB board design for many years of engineers, printed circuit board design experience to share with you. Welcome to collect!

For electronic products, PCB board design is a necessary design process from electrical schematic diagram to a specific product, and the rationality of its design is closely related to product production and product quality. However, for many people who are just engaged in electronic design, they have little experience in this aspect. Although they have learned PCB board design software, But PCB designs often have some problems. The engineer recommended by Xiaobian has been engaged in PCB board design for many years. He/she will share his/her experience in PRINTED circuit board design with you, hoping to play a role of casting a brick to attract jade. The PCB design software recommended by the engineer was TANGO a few years ago, and now uses PROTEL2.7 FOR WINDOWS.

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The usual order of placement of components on the PCB:

1, place the components with a fixed position closely with the structure, such as power socket, indicator light, switch, connector, etc., these components are placed after the LOCK function of the software to LOCK it, so that it will not be moved by mistake;

2, special components and large components placed on the line, such as heating elements, transformers, IC, etc.;

3. Place small devices.

Distance between the component and the edge of the PCB

If possible, all components should be placed within 3mm from the edge of the PCB board or at least greater than the thickness of the PCB board. This is because in mass production of assembly line plug-ins and wave soldering, it should be provided to the guide groove for use. At the same time, in order to prevent edge defects caused by shape processing, if there are too many components on the PCB board, If you have to go beyond the 3mm range, you can add a 3mm auxiliary edge to the edge of the PCB board, and open a V-shaped slot on the auxiliary edge, which can be broken by hand during production.

Isolation between high and low pressure

There are high voltage circuit and low voltage circuit at the same time on many PCB boards, the components of the high voltage circuit and the low voltage part should be separated and open, and the isolation distance is related to the withstand voltage. Normally, the PCB board should be 2mm away from the withstand voltage at 2000kV, and the proportion above this should be increased, for example, if the withstand voltage test is 3000V, The distance between the high and low voltage lines should be more than 3.5mm, in many cases to avoid creepage, but also in the PCB board between the high and low voltage slot.

PCB board cabling

The layout of printed conductors should be as short as possible, especially in high frequency circuits; The turning of printed wire should be rounded, and the right Angle or sharp Angle will affect the electrical performance in the case of high frequency circuit and wiring density; When wiring two panels, the wires on both sides should be perpendicular, oblique, or bent to avoid parallel to each other to reduce parasitic coupling. Printed wires used as input and output of the circuit should be avoided parallel to each other as far as possible to avoid feedback. It is best to add grounding wires between these wires.

Width of printed wire

The width of the wire should meet the requirements of electrical performance and be convenient for production. Its minimum value depends on the size of the current, but the minimum should not be less than 0.2mm. In high density, high precision printed lines, wire width and spacing is generally desirable 0.3mm; The temperature rise of wire width should be considered in the case of high current. The single-panel experiment shows that when the thickness of copper foil is 50μm, the width of wire is 1 ~ 1.5mm and the current is 2A, the temperature rise is very small. Therefore, the wire with the width of 1 ~ 1.5mm can meet the design requirements without causing the temperature rise.

Common ground wires for printed conductors should be as thick as possible, using lines larger than 2 to 3mm if possible, especially in circuits with microprocessors. Because the local line is too fine, due to the change of current flow, ground potential changes, microprocessor timing signal level instability, will make noise tolerance deterioration; The 10-10 and 12-12 principles can be applied when wiring between DIP packaged IC pins, that is, when two wires are passed between the pins, the pad diameter can be set to 50mil, line width and line spacing are 10mil, when only one wire is passed between the pins, the pad diameter can be set to 64mil, line width and line spacing are 12mil.

Spacing of printed wires

The spacing between adjacent wires must meet the requirements of electrical safety, and for the convenience of operation and production, the spacing should be as wide as possible. The minimum spacing must be at least suitable for the voltage to be sustained. This voltage generally includes the operating voltage, the additional fluctuation voltage and the peak voltage caused by other reasons.

If the technical conditions permit some degree of metal residue between wires, the spacing will be reduced. The designer should therefore take this factor into account when considering voltage. When wiring density is inferior, the spacing of signal line can increase appropriately, the signal line with great disparity of high, low level should be short as far as possible and increase spacing.

Shielding and grounding of printed wires

The public ground wire of the printed wire shall be arranged on the edge of the printed circuit board as far as possible. As much copper foil as possible should be reserved as ground wire on PCB board, so that the shielding effect is better than a long ground wire, transmission line characteristics and shielding effect will be improved, and also play a role in reducing the distributed capacitance. The public ground wire of printed wire is best to form a loop or network, because when there are many integrated circuits on the same board, especially when there are components that consume more power, the limitation on the graph produces the grounding potential difference, which causes the reduction of noise tolerance, when it becomes a loop, the grounding potential difference is reduced.

In addition, the ground and power diagram should be parallel to the flow direction of data as far as possible, which is the secret of enhanced noise suppression ability; Multilayer PCB board can take several layers as shielding layer, power supply layer, ground layer can be regarded as shielding layer, general ground layer and power layer are designed in the inner layer of multilayer PCB board, signal line design inner layer and outer layer.