Detailed explanation of design method of PCB wiring, welding pad and copper coating

With the progress of electronic technology, the complexity of PCB (printed circuit board), the scope of application has a rapid development. Designers engaged in HF PCB must have relevant basic theoretical knowledge and rich experience in THE manufacture of HF PCB. In other words, both schematic drawing and PCB design should be considered from the high-frequency working environment, so as to design a more ideal PCB.


This paper, a PCB wiring, welding plate and apply the design method of copper, first of all, on the base of the PCB wiring, wiring, the power cord and the ground wiring requirements in the form of the paper introduces the design of the PCB wiring, second from the bonding pad and aperture, PCB pad size and shape of design in the design of the standard, the requirements of PCB manufacturing process pads are introduced the design of the PCB solder, Finally, from the PCB copper coating skills and Settings introduced the PCB copper coating design, specific follow xiaobian to understand.

Detailed explanation of design method of PCB wiring, welding pad and copper coating

PCB wiring design

Wiring is the general requirement of hf PCB design based on reasonable layout. Cabling includes automatic cabling and manual cabling. Usually, no matter how many key signal lines there are, manual wiring should be carried out for these signal lines first. After wiring is completed, the wiring of these signal lines should be carefully checked and fixed after passing the check, and then other cables should be automatically wired. That is, the combination of manual and automatic wiring is used to complete PCB wiring.

The following aspects should be paid special attention to during the wiring of hf PCB.

1. The direction of wiring

The wiring of the circuit is best to adopt a full straight line according to the direction of the signal, and 45° broken line or arc curve can be used to complete the turning point, so as to reduce the external emission and mutual coupling of high-frequency signals. The wiring of high frequency signal cables should be as short as possible. According to the working frequency of the circuit, the length of the signal line should be reasonably selected, so as to reduce the distribution parameters and reduce the loss of the signal. When making double panels, it is best to route the two adjacent layers vertically, diagonally or bent to intersect each other. Avoid being parallel to each other, which reduces mutual interference and parasitic coupling.

High frequency signal lines and low frequency signal lines should be separated as far as possible, and shielding measures should be taken when necessary to prevent mutual interference. For the signal input receiving relatively weak, easy to be interfered by external signals, you can use the ground wire to do shielding to surround it or do a good job of high-frequency connector shielding. Parallel wiring should be avoided on the same level, otherwise distributed parameters will be introduced, which will affect the circuit. If unavoidable, a grounded copper foil can be introduced between the two parallel lines to form an isolation line.

In the digital circuit, for differential signal lines, should be in pairs, as far as possible to make them parallel, close to some, and the length is not much different.

2. The form of wiring

In PCB wiring, the minimum width of the wiring is determined by the adhesion strength between the wire and the insulator substrate and the strength of the current flowing through the wire. When the thickness of copper foil is 0.05mm and the width is 1mm-1.5mm, 2A current can be passed. The temperature should not be higher than 3 ℃. Except for some special wiring, the width of other wiring on the same layer should be as consistent as possible. In high frequency circuit, the spacing of wiring will affect the size of distributed capacitance and inductance, and thus affect the signal loss, circuit stability and signal interference. In high speed switching circuit, wire spacing will affect signal transmission time and waveform quality. Therefore, the minimum spacing of the wiring should be greater than or equal to 0.5 mm. It is best to use wide lines for PCB wiring whenever possible.

There should be a certain distance between the printed wire and the edge of the PCB (no less than the thickness of the plate), which is not only easy to install and machining, but also improve the insulation performance.

When wiring can only be connected around a large circle of the line, we should use the flying line, that is, directly connected with short line to reduce the interference brought by long-distance wiring.

The circuit containing magnetic sensitive elements is sensitive to the surrounding magnetic field, while the bend of wiring of high-frequency circuit is easy to radiate electromagnetic wave. If magnetic sensitive elements are placed in PCB, it should ensure that there is a certain distance between the corner of wiring and it.

No crossover is allowed on the same level of wiring. For the line that may cross, can use “drill” with “wound” method to solve, let a certain lead namely from other resistance, capacitance, audion etc. device lead foot gap place “drill” past, or from the end of a certain lead that may cross “wound” past. In special cases where the circuit is very complex, to simplify the design, it is also allowed to solve the crossover problem with wire bonding.

When the high frequency circuit operates at a high frequency, the impedance matching and antenna effect of wiring should also be considered.

Because the client finally changed the previous agreement and required the interface definition and placement as defined by them, they had to change the layout to the diagram on the right. In fact, the entire PCB is only 9cm x 6cm. It is difficult to change the overall layout of the board according to the requirements of customers, so the core part of the board was not changed in the end, but the peripheral components were modified appropriately, mainly the position of the two connectors and the definition of pins were modified.

But the new layout obviously caused some trouble in the line, the original smooth line became a little messy, the length of the line increased, but also had to use a lot of holes, the difficulty of the line increased a lot.

Detailed explanation of design method of PCB wiring, welding pad and copper coating

It is clear from this example that layout differences can have an impact on PCB design.

Detailed explanation of design method of PCB wiring, welding pad and copper coating

3. Wiring requirements for power cables and ground cables

Increase the width of the power cord according to different working current. Hf PCB should adopt large area ground wire and layout on the edge of PCB as far as possible, which can reduce the interference of external signal to the circuit; At the same time, the grounding wire of PCB can be in good contact with the shell, so that the grounding voltage of PCB is closer to the earth voltage. The grounding mode should be selected according to the actual situation. Different from the low-frequency circuit, the grounding cable of the high-frequency circuit should be nearby or multi-point grounding. The grounding cable should be short and thick to minimize the ground impedance, and the allowable current should be three times of the working current. The speaker grounding wire should be connected to the PCB power amplifier output level grounding point, do not arbitrarily grounding.

In wiring process still should be in time a few reasonable wiring lock, lest repeat wiring for many times. To lock them, run the EditselectNet command to select Locked in the pre-wired properties.