For electronic products, printed circuit board design is turning it into a specific product must go through a design process from electrical schematics, rationality and product design and product quality is closely related to , and for many newly engaged in electronic design the staff, with less experience in this regard , although the PCB design software has been learned , but the design of printed circuit boards often have this kind of problem, and many rare article describes electronic publications in this regard , I worked for many years in the PCB design work in this bit of the PCB design experience to share with you , hoping to play a valuable role. A few years ago the author of PCB design software is TANGO, now use PROTEL2.7 FOR WINDOWS.
First, the board layout
1 , usually placed in the order of components on printed circuit boards
Placed close coordination with the structure of the components of a fixed location , such as electrical outlets , lights , switches, connectors of the class , a good place these devices using the software after the LOCK function to lock it , the future will not be moved by mistake to make ;
Special components and large components placed on the line , such as heating elements , transformers , IC and so on.
2 , place a small device
The distance from the edge of the board components : possible all components are placed away from the edge of the plate thickness of less than 3mm or greater than at least , this is due to the mass production of plug-ins and pipeline flow soldering , to be provided to guide groove when in use, but also to prevent the defects caused by trimming the edge portions of the printed circuit board components , if too much forced to exceed the range of 3mm , 3mm can be added in the secondary -side edge of the plate , the open side of the V-shaped auxiliary slot in the production of hand snapping to .
Isolation between the high and low : in many high-voltage circuits and printed circuit boards also have low-voltage circuits , components, and parts of the low-pressure part of the high-voltage circuit to separate the open position, the isolation distance and pressure to bear about , usually in 2000kV when the board to distance 2mm, on this count also increased in proportion , such as to withstand 3000V withstand voltage test , the distance between the high and low voltage lines should be 3.5mm or more, in many cases in order to avoid creepage , still slotted between the high and low pressure on the PCB .
Second, the PCB traces :
Printed conductors should be as short as possible emplaced in high-frequency circuits and even more so ; printed conductors should be rounded the corner , and at right angles or sharp corners at high frequency circuits and wiring density will affect the electrical properties ; when the two panel wiring , both sides of the wire should be perpendicular , oblique or curved alignment, avoiding parallel to each other , in order to reduce the parasitic coupling as input and output circuits printed adjacent parallel wires should be avoided in order to avoid feedback occurs between these wires plus ground wire is best .
Printed wire width: wire width should be able to meet the electrical performance requirements but is easy to produce appropriate, its minimum to withstand the current size of , but not less than the minimum 0.2mm, printed on high-density, high-precision line , the wire width and spacing is generally preferable to 0.3mm; wire width at high current situation but also consider the temperature, single-panel experiment showed that when the foil thickness is 50μm, wire width 1 ~ 1.5mm, through the current 2A, temperature is small , and therefore , is generally used in 1 ~ 1.5mm conductor width may satisfy design requirements without causing temperature ; printed wire should be as thick common ground , if possible , 2 ~ 3mm larger than the line , this is particularly important in the circuit with a microprocessor , the local line because too small, due to changes in current flow , changes in the ground potential , the signal level of the timing instability of the microprocessor , causes deterioration of the noise margin ; Walking the line between the IC pin DIP package , 10-10 and 12-12 can be applied the principle that when the time between the legs by two lines, pad diameter can be set to 50mil, line width and line spacing are 10mil, when time feet through only one line , pad diameter can be set to 64mil, line width and line spacing are 12mil.
Third, the printed wire spacing
Adjacent wire spacing must be able to meet the electrical safety requirements , and in order to facilitate the operation and production , the spacing should be as wide as some . Minimum distance at least be able to fit withstand voltage. This voltage is typically the operating voltage, and the peak voltage of the additional voltage fluctuations due to other causes . If the technical conditions allow a degree of residual particles between the metal wires , the spacing is reduced . Therefore, the designer should consider the voltage in such factors into account . At lower wiring density , the spacing of signal lines can be appropriately increased to high and low disparity signal lines should be as short as possible and increase the spacing.
Fourth, the printed conductors and the ground shield
Printed wire common ground , should be arranged at the edge of printed circuit boards . On the printed circuit board should be retained as much as possible to make the ground foil shielding effect thus obtained is better than a strip of ground , the shielding effect of the transmission line characteristics will be improved and , in addition play a role in reducing the distributed capacitance . Printed common ground wire or mesh loops are preferably formed , this is because when the same board with many integrated circuits, and more particularly with the power element, due to limitations of the ground pattern on the potential difference generated , thereby reducing the noise caused by the tolerance , the circuit formed when the ground potential difference decreases . Further , as the ground and power to the graphics data in parallel with the flow direction , which is the secret to enhanced noise suppression capability ; multilayer printed wiring board wherein a plurality of layers may be taken as a shielding layer, power supply layer , a ground layer can be as to shield the general design of the ground and power planes in the inner layer of a multilayer printed circuit board , the signal line design in inner and outer layers .
