PCB are important electronic components, and is the origin of all electronic components, from the beginning of ShangShi appear to now also becomes more and more complex, from single to double, four layers, then to multilayer and design difficulty is also increasing.Because the two sides of the double board have wiring, it is very helpful for us to understand and master its wiring principles.Let’s take a look at the wiring principles of the PCB double board.
PCB ground double plate designed fence around the box form, namely in the PCB side cloth more parallel to the ground, the other side is vertical ground wire copy board, then where they cross connect with metallized via (via resistance smaller).
Considering that there should be a ground line near each IC chip, a ground line is usually made every 1 ~ 115cm, which makes the area of signal loop smaller, which is conducive to reducing radiation.The network design method should be before the signal line, otherwise the implementation is difficult.
Wiring principle of signal line:
After determining the reasonable layout of the components, the double-layer board is followed by the design of the power cord of the ground screen, and then the important line – the sensitive line, the high frequency line, and the back cloth general line – the low-frequency line.The key leads have to have a separate power source, ground wire loop, lead wire and very short, so sometimes a ground line near the key line is close to the signal line so that it can form the smallest working loop.
Four layer board with double top surface, bottom of the wiring board signal lines, was a key crystal cloth first, crystals circuit, clock circuit, signal lines, such as CPU must abide by the principle of circulation area of small as far as possible.
When the printing plate IC circuit works, the circulation area is mentioned many times before, and it is in fact the concept of differential mode radiation.Such as the definition of differential mode radiation: circuit work current to flow in the signal circuit, the signal loop will produce electromagnetic radiation, is due to the current differential mode, so called differential mode signal loop produced by radiation radiation, the calculation formula of radiation field intensity:
E1 = K1, f2, i. a. / gamma
Type: E1 – differential mode copy board, PCB circuit of space gamma radiation field intensity by differential mode radiation formula can be seen, the radiation field intensity and working frequency f2, A circulation area, the working current is proportional to the, I like when the working frequency f is determined, the size of the circulation area is that we can directly control the key factors in the design, at the same time circulation work as long as meet reliability, speed, current is not the bigger the better, the narrower the dance along the edge on the signal, the greater the harmonic component of it, the more wide, the higher the electromagnetic radiation, the greater the power of its current necessarily has pointed out (above), we don’t expect it.
Key connections, if possible, surround them with ground lines.After another for PCB copy board wiring, the available ground cover all the gap, but must pay attention to all these covers the ground will be short and big couplet of formation of low impedance, so can obtain good result (note: there is a requirement for space shall meet the conditions, such as creepage distance).