It is necessary to know PCB process the size of the five principles
1, printing selecting wire width: lead the minimum width is related to the size of the current through the wire, PCB line width is too small, just printing conductor resistance is big, line voltage drop is big, the influence on the performance of the circuit board circuit, line width is too wide, the wiring density is not high, the PCB area increase, in addition to increasing cost, is unfavorable to miniaturization. If the current load on 20 a/mm2 calculation, when copper-clad thickness of 0. 5 mm, For so many commonly,) The 1 mm ( About 40 mil) Line width of the current load to 1 a, therefore, line width 1, & # 8211; 2. 54MM( 40 - 100MIL) Can meet the application requirement of general, power equipment on board ground wire and power supply, according to the power size, can be appropriately increase the line width, and in the number of small power circuit, in order to improve the wiring density, the minimum line width 0. 254 - 1. 27MM( 10 - 15MIL) They can satisfy. In the same circuit board, the power cord. Ground wire thicker than signal lines. 2 double-sided circuit boards, PCB line spacing: when to 1. 5MM( About 60 mil) , the insulation resistance between the line, more than 20 m o line between maximum pressure of up to 300 v, when the line spacing to 1 mm ( 40MIL) , the line between maximum withstand voltage of 200 v, therefore, in the low-pressure ( Line to line voltage is not greater than 200 v) Take 1 of circuit boards, line spacing. 0 - 1. 5毫米( 40 - 60MIL) In low voltage circuit, such as digital circuit in the system, needn't consider the breakdown voltage, as long as allow production technology, can be very small. 3, welding plate: for the 1/8 w resistor, the solder wire diameter 28 mil is enough, for 1/2 w, diameter of 32 mil, pin hole slants big, solder copper ring width decrease relatively, resulting in a decline in the adhesion of the welding plate. Easy to fall off, hole is too small, lead components with difficulty. 。 4, draw PCB circuit frame: border lines and element pin solder shortest distance not less than 2 mm, ( A reasonable generally take 5 mm) Otherwise the blanking difficulty. 5, the principle of component placement: A. General principles: in PCB design, if the system analog and digital circuit circuit. And big current circuit, you must separate layout, make to minimize the coupling between the various systems in the same type of circuit, and according to the signal flow to and function of block, partition place component. B。 Components placed direction: components can only be arranged along the horizontal and vertical two direction. In the plug-in. C。 When the potential difference is larger between components, element spacing should be large enough, prevent discharge phenomenon. D。 Input signal processing unit and output signal driving element should be near a circuit board, the input and output signal lines as short as possible, to reduce the interference of input and output. E. Element spacing. For medium density board, the small components, such as small power resistor, capacitor, diode, such as discrete element spacing and plug-ins, welding technology, wave soldering, can take 50 - element spacing 100MIL( 1. 27 - 2. 54MM) Manual can be bigger, such as take 100 mil, integrated circuit chips, element spacing shall generally be 100 & # 8211; 150MIL 。 F。 In just into the IC to lotus root power capacitor close to chips fall ground pins. Otherwise the filtering effect will be worse. In digital circuit, digital circuit system in order to ensure the reliable work, in every digital integrated circuit chips are placed between power supply and ground IC to coupling capacitance. Decoupled commonly used ceramics capacitors, capacity of 0. 01 ~ 0. The selection of uf to lotus root capacitance in according to the reciprocal of system working frequency F choices. In addition, at the entrance of the power supply circuit of the power cord between the ground and also need to add a 10 uf capacitance, and a 0. 01 uf ceramics capacitors. 。 G。 Clockwise circuit element near the microcontroller chip clock signal pin, as far as possible to minimize clock circuit connection length. And here it is best not to go.