For electronic products, PCB design is from the electrical schematic diagram into a specific product must be a design process, the design of the rationality of production and product quality is closely related to, and for many people just engaged in electronic design In this regard, less experience in this area, although has learned the PCB board design software, but the design of the PCB board often have such a problem. Xiaobian recommended engineers have been engaged in PCB board design work for many years, will be printed circuit board design experience and share with you, hoping to play a role. Xiaobian recommended engineers printed circuit board design software is a few years ago is TANGO, now use PROTEL2.7 FOR WINDOWS.

PCB layout:

PCB board components placed in the usual order:
1, place a fixed position with the structure of the components, such as power outlets, lights, switches, connectors and the like, these devices are placed after the software with the LOCK function to lock it, so that it will not be wrong mobile;
2, the placement of special components on the line and large components, such as heating elements, transformers, IC, etc .;
3, place a small device.

The distance from the edge of the PCB board:
If possible, all components are placed within 3mm from the edge of the PCB or at least greater than the thickness of the PCB. This is due to the use of the rails in mass production and for wave soldering. Due to the shape of the edge caused by the part of the defect, if the PCB board components too much, had to go beyond the 3mm range, you can add the edge of the PCB board 3mm auxiliary side, auxiliary side open V-shaped slot, Can be broken off.

Isolation between high and low pressure:
In many PCB board at the same time there are high-voltage circuit and low-voltage circuit, high-voltage circuit part of the components and low-voltage parts to be separated from the isolation distance to bear the pressure, usually under 2000kV PCB board to distance 2mm , In order to increase the proportion of the above, for example, to withstand the 3000V pressure test, the distance between high and low voltage lines should be more than 3.5mm, in many cases to avoid creeping, still on the PCB board The gap between the high and low pressure.

PCB board alignment:
The printed wire should be laid out as short as possible and should be so high in high frequency circuits; the corners of the printed wire should be rounded and the right angle or sharp corners may affect the electrical performance in the case of high frequency circuits and high wiring densities ; When the two panels wiring, the two sides of the wire should be perpendicular to each other, oblique, or curved alignment, to avoid parallel to each other to reduce the parasitic coupling; as the circuit input and output printed wire should try to avoid adjacent parallel, To avoid the occurrence of feedback, between these wires is best to add ground wire.

Width of printed wire:
Wire width should be able to meet the electrical performance requirements and easy to produce appropriate, its minimum value to bear the size of the current, but the minimum should not be less than 0.2mm. In the high-density, high-precision printed circuit, the wire width and spacing is generally desirable 0.3mm; wire width in the case of high current but also consider its temperature rise, single-panel experiments show that when the copper foil thickness of 50μm, wire width 1 ~ 1.5mm, through the current 2A, the temperature rise is very small, therefore, generally use 1 ~ 1.5mm width of the wire may meet the design requirements without causing temperature rise.

The common ground of the printed wire should be as thick as possible, and if possible, use lines greater than 2 to 3 mm, which is particularly important in circuits with microprocessors. Because the local line is too fine, due to changes in the current flow, ground potential changes, the microprocessor timing signal level instability, will make the noise margin degradation; in the DIP package IC pin between the line, 10 and 12-12 principle, that is, when the two lines between the two lines, the pad diameter can be set to 50mil, line width and line spacing are 10mil, when the two feet only through a line, the pad diameter Set to 64mil, line width and line spacing are 12mil.

Printed wire spacing:
Adjacent conductor spacing must meet electrical safety requirements, and for ease of operation and production, the spacing should be as wide as possible. Minimum spacing at least to be able to withstand the voltage. This voltage typically includes the operating voltage, the additional ripple voltage, and other causes of the peak voltage.

If the technical conditions allow a certain degree of metal residue between the wires, the spacing will be reduced. So the designer should take this factor into account when considering the voltage. When the wiring density is low, the pitch of the signal lines can be appropriately increased, and the signal lines for the high and low levels should be as short as possible and the pitch can be increased.

Printed and shielded wire:
Printed conductor of the public ground, should be arranged in the printed circuit board edge part. In the PCB board should be as much as possible to retain the copper foil to do the ground, so get the shielding effect, better than a long ground, transmission line characteristics and shielding effect will be improved, and the other played a role in reducing the distributed capacitance. The common ground of the printed wire is preferably looped or reticulated because when there are many integrated circuits on the same board, especially when there are more power consuming components, the ground potential difference is generated due to graphical limitations , Resulting in reduced noise margin, when made into a loop, the ground potential difference decreases.

In addition, the ground and power of the graphics as much as possible with the data flow direction parallel, which is to suppress the noise enhancement of the secret; multi-layer PCB board can take a number of layers for the shield, power layer, ground layer can be regarded as shielding The layers, the general ground layer and the power plane are designed in the inner layer of the multilayer PCB board, and the signal lines are designed in the inner and outer layers.