Some minor principles of the PCB replication process
1: Print line width selection: The minimum width of the printed line is related to the current flowing through the wire: the line width is too small, the resistance of the printed line is large, and the voltage drop on the line is large, which affects the performance of the circuit. If the width is small, the wiring density is not high, and the substrate area is increased. In addition to increasing costs, it is also disadvantageous for miniaturization. If the current load is calculated at 20 A / mm 2 , when the thickness of the copper clad is 0.5 MM (usually the case), the current load with a line width of 1 MM (about 40 mil) is 1 A, so the line width is 1- 2.54. MM (40-100MIL) can meet the general application requirements. The ground and power supplies on the high-power device board increase the line width according to the power. In low-power digital circuits, in order to increase the wiring density, the minimum line width is 0.254-1.27 MM (10-15 MIL). On the same board, the power cord. The ground wire is thicker than the signal wire.
2: Line spacing: When it is 1.5MM (about 60 MIL), the insulation resistance between wires is greater than 20M ohms, and the maximum withstand voltage between wires can reach 300V. When the line spacing is 1 MM (40 mil), the maximum withstand voltage between the lines is 200V. Therefore, on medium and low voltage circuit boards (line voltage is not more than 200V), the line spacing is 1.0-1.5MM (40-60 MIL). In a low voltage circuit such as a digital circuit system, there is no need to consider the breakdown voltage. The production process allows, can be small.
3: Pad: For a 1 / 8W resistor, the pad lead diameter is 28 MIL is sufficient; for 1/2 W, the lead diameter is 32 MIL, the lead hole is larger, and the pad copper ring width is relatively reduced Small. , causing the adhesion of the pad to decrease. It is easy to fall off, the lead hole is too small, and the component installation is difficult.
4: Draw the circuit frame: The shortest distance between the frame wire and the component lead pad cannot be less than 2MM (usually 5MM is reasonable), otherwise it is difficult to cut.
5: Component layout principle: A: General principle: In the PCB design, whether there are digital circuits and analog circuits in the circuit system. As with high current circuits, they must be arranged separately so that matching between systems can be minimized in the same type of circuit and components placed in the direction of signal flow and function, division and division.
6: Input signal processing unit, the output signal drive component should be close to the edge of the board, so that the input and output signal lines are as short as possible to reduce input and output interference.
7: Component placement direction: The components can only be arranged horizontally and vertically. Otherwise, it will not be allowed in the plugin.
8: Component spacing. For medium density boards, small parts such as small power resistors, capacitors, diodes, etc., the spacing between discrete components is related to the insertion and soldering process. When soldering, the component spacing can be 50-100 MIL (1.27-2.54MM). For larger integrated circuit chips (eg 100 MIL), the component spacing is typically 100-150 MIL.
9: When the potential difference between components is large, the component spacing should be large enough to prevent discharge.
10: In the IC, the tantalum capacitor is close to the power line of the chip. Otherwise the filtering will be worse. In digital circuits, to ensure reliable operation of the digital circuitry, an IC decoupling capacitor is placed between the power supply of each digital integrated circuit chip and ground. Tantalum capacitors are generally made of ceramic capacitors and have a capacity of 0.01 to 0.1 UF. The capacity of the tantalum capacitor is typically selected based on the reciprocal of the system operating frequency F. In addition, a 10UF capacitor and a 0.01UF ceramic capacitor are required between the power and ground wires at the circuit power inlet.
11: The hour hand circuit component is as close as possible to the clock signal pin of the microcontroller chip to shorten the connection length of the clock circuit. It is best not to go offline.