Printed Circuit Board Assembly

PCB Assembly

Some small principles of PCB copy board technology

 Some small principles of PCB copy board technology
1: Printed wire width selection basis:
The minimum width of the printed wire and the current flow through the wire size: line width is too small, just printed wire resistance, the line voltage drop is also large, affecting the circuit performance, line width is too wide, the wiring density is not high, If the current load is calculated as 20A / mm2, when the thickness of the copper foil is 0.5mm (usually so much), the 1MM (about 40MIL) linewidth is the same as the increase in the board area. Of the current load of 1A, therefore, line width of 1--2.54MM (40-100MIL) to meet the general application requirements, high-power equipment board on the ground and power, according to the power size, may be appropriate to increase the line width, In the small-power digital circuit, in order to improve the wiring density, the minimum line width to take 0.254--1.27MM (10--15MIL) will be able to meet the same circuit board, the power line. Ground than the signal line thick.
2: Line spacing:
When the 1.5MM (about 60MIL), the line between the insulation resistance is greater than 20M Europe, the line between the maximum voltage up to 300V, when the line spacing of 1MM (40MIL), the line between the maximum voltage of 200V, Low voltage (line voltage of not more than 200V) on the circuit board, the line spacing to take 1.0-1.5MM (40--60MIL) in low-voltage circuits, such as digital circuit system, do not have to consider the breakdown voltage, as long as the production process allows Very small
3: Pad:
For 1 / 8W resistance, the lead wire diameter of 28MIL is sufficient, and for 1 / 2W, the diameter of 32MIL, the lead hole is too large, the pad copper ring width is relatively reduced, resulting in the pad The adhesion is reduced, it is easy to fall off, the lead hole is too small, and the component sowing is difficult.
4: draw circuit border:
Border line and component pin pad the shortest distance can not be less than 2MM, (generally take 5MM more reasonable) Otherwise, the next difficult.
5: component layout principles:
A: General principles: In the PCB design, if the circuit system and the existence of digital circuits and analog circuits, as well as high current circuit, you must separate the layout, so that the coupling between the system to achieve the smallest in the same type of circuit, Function, block, partition placed components.
B: input signal processing unit, the output signal drive components should be close to the circuit board side, so that input and output signal lines as short as possible to reduce the input and output interference.
C: Component orientation: The element can only be arranged in both horizontal and vertical directions, otherwise it must not be inserted.
D: component spacing. For medium density boards, small components, such as small power resistors, capacitors, diodes, and other discrete components of the distance between the plug and the welding process, the wave soldering, the component spacing can take 50-100MIL (1.27-- 2.54MM) manual can be larger, such as take 100MIL, integrated circuit chip, component spacing is generally 100-150MIL
E: When the potential difference between the components is large, the component spacing should be large enough to prevent the discharge phenomenon.
In the digital circuit, in order to ensure reliable operation of the digital circuit system, the power supply in each digital integrated circuit chip and the power supply of the digital circuit in the digital circuit, The earth is placed between the IC to the lotus capacitor.To the lotus capacitor is generally used ceramic capacitors, the capacity of 0.01 ~ 0.1UF to the lotus capacitor capacity selection is generally selected according to the system operating frequency F.In addition, the circuit power at the entrance of the Power lines and ground between the need to add a 10UF capacitor, and a 0.01UF ceramic capacitors.
G: clock circuit components as close as possible to the microcontroller chip clock signal pin to reduce the length of the clock circuit connection. And the following is best not to line
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