PCB board selection
PCB board is generally made of copper laminates, board selection from the electrical performance, reliability, processing technology requirements and economic indicators and other considerations. Common copper laminates are copper phenolic paper laminates, copper-coated epoxy paper laminates, copper-coated epoxy glass cloth laminates, copper-clad epoxy phenolic glass cloth laminates, copper-coated polytetrafluoroethylene glass Cloth laminates and multilayer printed circuit boards with epoxy glass cloth and so on. Different materials of the laminate has different characteristics. Epoxy resin and copper foil has an excellent adhesion, so the copper foil adhesion strength and operating temperature is high, can be 260 ℃ in the melting tin does not blister. Epoxy resin-impregnated glass cloth laminates are less affected by moisture. Ultra-high frequency circuit board is best deposited copper polystyrene glass cloth laminate. In the requirements of flame-retardant electronic equipment, also need flame retardant PCB board, these PCB board are immersed in the flame retardant resin laminate.

PCB board size
PCB board thickness should be based on the PCB board function, the weight of components installed, PCB board socket specifications, PCB board size and bear the mechanical load to decide. Mainly should ensure sufficient rigidity and strength.

Common PCB thickness: 0.5mm, 1.0mm, 1.5mm, 2.0mm.

From the cost, copper wire length, anti-noise ability to consider, PCB board size as small as possible. But the PCB board size is too small, the poor heat dissipation, and adjacent wires easily lead to interference. PCB board production costs and PCB board area is related to the larger, the higher the cost. PCB board size in the design of the PCB board size is also limited by the size of the chassis shell, be sure to determine the size of the PCB board to determine the size of the shell, otherwise it can not determine the PCB board size. In general, the wiring range specified in the forbidden wiring layer is the size of the PCB size.

PCB board is the best shape of rectangular, aspect ratio of 3: 2 or 4: 3, when the PCB board size is greater than 200 * 150mm, PCB board should consider the mechanical strength. In short, should consider the pros and cons to determine the PCB board size.

PCB board component layout
Although the Protel DXP can automatically layout, but in fact the layout of the PCB board components are almost always done by hand. PCB board components generally follow the following rules:

1, special components layout

The layout of special components from the following aspects:

1) high frequency components

The connection between the high-frequency components is as short as possible, trying to reduce the distribution of the parameters of the connection and the electromagnetic interference between each other, vulnerable components can not be too close. The distance between the components belonging to the input and the components belonging to the output should be as large as possible.

2) Components with high potential difference

The distance between the components with high potential difference and the connection should be increased to avoid damage to the components when an unexpected short circuit occurs. In order to avoid the occurrence of creepage phenomenon, generally require 2000V potential difference between the copper film line distance should be greater than 2mm, if the higher potential difference, the distance should also increase. With high voltage devices, should be arranged as far as possible when debugging difficult to reach the place.

3) Components that are too heavy

Such components should have a fixed bracket, and for large and heavy, more heat and more components, should not be installed on the PCB board.
 
4) heat and thermal components

Note that the heating element should be away from the thermal element.

5) can adjust the components

For the potentiometer, adjustable inductance coil, variable capacitor, micro switch and other adjustable components of the layout should consider the structural requirements of the machine, if the machine is adjusted, should be placed on the PCB board easy to adjust the place, if the machine outside the regulation , Which corresponds to the position of the adjustment knob on the chassis panel.

6) Board mounting holes and bracket holes

The mounting holes of the PCB board and the mounting holes of the brackets should be reserved because they can not be routed near the holes and holes.