mixed-威尼斯886699

1. printing selecting wire width: lead the minimum width is related to the size of the current through the wire: line width is too small, just printing conductor resistance is big, line voltage drop is big, also affect the performance of the circuit, line width is too wide, the wiring density is not high, plate area increase, in addition to increasing cost, is unfavorable to miniaturization. if the current load on 20 a/mm2 calculation, when the thickness of 0.5 mm copper foil (for so many, commonly) is 1 mm (about 40 mil) line width of the current load to 1 a, therefore, line width 1-2.54 mm (40-100 mil) can meet the application requirement of general, plate on the ground and the power of high power devices, 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, minimum line width 0.254-1.27 mm (10 -- 15 mil) can meet. in the same circuit board, the power cord. ground wire thicker than signal lines.

2. line spacing: when is 1.5 mm (about 60 mil), the insulation resistance between the line more than 20 m euro, line between maximum pressure of up to 300 v, when the line spacing of 1 mm (40 mil), the line between maximum withstand voltage is 200 v, therefore, in the low-pressure (line to line voltage is not greater than 200 v) of circuit boards, 1.0-1.5 mm spacing between 40-60 (mil) 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. the bonding pad: for the 1/8 w resistor 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 circuit frame: border lines and element pin solder shortest distance not less than 2 mm, more reasonable (generally take 5 mm) or cutting difficult.

5. component placement principle: a: the general principle: in the 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.

6. the input signal processing unit, output signal driving element should be near a circuit board, the input and output signal lines as short as possible, to minimize the interference of input and output.

7. components placed direction: components can only be arranged along the horizontal and vertical two direction. in the plug-in.

8. 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, element spacing can take 50-100 mil (1.27-2.54 mm) by hand can be bigger, such as take 100 mil, integrated circuit chips, element spacing generally is 100-150 mil.

9. when the element potential difference between the larger, element spacing