Some small principles of PCB copy board process
1: The basis for selecting the width of the printed wire: The minimum width of the printed wire is related to the amount of current flowing through the wire: the line width is too small, the resistance of the printed wire is large, and the voltage drop on the line is large, affecting the performance of the circuit. Wide, the wiring density is not high, the board area increases, in addition to increasing costs, it is not conducive to miniaturization. If the current load is calculated at 20A / mm2, when the thickness of the copper foil is 0.5MM, (usually so much), the current load of 1MM (about 40MIL) line width is 1A, so the line width is 1-2.54 MM (40—100MIL) can meet the general application requirements. The ground wire and power supply on the high-power equipment board can be appropriately increased according to the power. On the low-power digital circuit, in order to improve the wiring density, the minimum Line width can be satisfied by taking 0.254-1.27MM (10-15MIL). In the same circuit board, the power cord. The ground wire is thicker than the signal wire.
2: Line spacing: When it is 1.5MM (about 60MIL), the insulation resistance between lines is greater than 20M ohms, and the maximum withstand voltage between lines can reach 300V. When the line spacing is 1MM (40MIL), the maximum withstand voltage between lines is 200V Therefore, on medium and low voltage (the line-to-line voltage is not greater than 200V), the line spacing is 1.0——1.5MM (40—60MIL). In low voltage circuits, such as digital circuit systems, it is not necessary to consider the breakdown voltage, as long as The production process allows and can be small.
3: Pad: For a 1 / 8W resistor, a pad lead diameter of 28MIL is sufficient, while for a 1 / 2W, the diameter is 32MIL, the lead hole is too large, and the pad copper ring width is relatively reduced. , Resulting in a decrease in the adhesion of the pad. Easy to fall off, lead holes are too small, and component placement is difficult.
4: Draw the circuit frame: the shortest distance between the frame line and the component pin pads cannot be less than 2MM, (generally 5MM is more reasonable), otherwise it is difficult to cut the material.
5: Component layout principles: A: General principles: In the PCB design, if the circuit system has both digital and analog circuits. As well as high-current circuits, they must be laid out separately to minimize the integration between various systems. In the same type of circuit, components are placed in blocks and partitions according to the signal flow and function.
6: The input signal processing unit, the output signal driving component should be close to the edge of the circuit board, make the input and output signal lines as short as possible to reduce the input and output interference.
7: Component placement direction: Components can only be arranged in both horizontal and vertical directions. Otherwise it cannot be used for plug-ins.
8: Component pitch. For medium-density boards, the distance between small components such as low-power resistors, capacitors, diodes, and other discrete components is related to the plug-in and the welding process. When wave soldering, the component distance can be 50-100MIL (1.27-2.54MM) manually. Larger, such as taking 100MIL, integrated circuit chips, the component pitch is generally 100-150MIL.
9: When the potential difference between the components is large, the component spacing should be large enough to prevent discharge.
10: Go into the IC. The capacitor should be close to the power supply ground pin of the chip. Otherwise the filtering effect will be worse. In digital circuits, to ensure the reliable operation of digital circuit systems, IC decoupling capacitors are placed between the power and ground of each digital integrated circuit chip. The decoupling capacitors are generally ceramic capacitors with a capacity of 0.01 ~ 0.1UF. The selection of the decoupling capacitor capacity is generally based on the reciprocal of the system operating frequency F. In addition, a 10UF capacitor and a 0.01UF ceramic capacitor should be connected between the power line and the ground at the entrance of the circuit power supply.
11: The hour hand circuit components should be as close as possible to the clock signal pins of the microcontroller chip to reduce the wiring length of the clock circuit. And it is best not to run the wiring below.