In the PCB board design, wiring is an important step to complete the product design, it can be said that the preparatory work is done for it. In the design of the PCB board to the wiring design process to limit the highest, the finest techniques, the largest workload. PCB board wiring single-sided wiring, double-sided wiring and multi-layer wiring. PCB board wiring there are two ways: automatic routing and interactive wiring. Before the automatic routing, you can use the interactive pre-required more stringent wiring. The edges of the input and output should be prevented from being parallel to each other in order to avoid reflection interference. If necessary, add ground isolation. The wiring of two adjacent layers should be perpendicular to each other, and the parasitic coupling is easy to occur in parallel.

PCB board automatic routing of the cloth rate, depending on the layout of a good PCB board, wiring rules can be set in advance, including the number of bending the number of holes, the number of vias, the number of steps and so on. Generally first to explore the type of cloth warp, quickly connected to the short-term, and then the labyrinth of the wiring, the first cloth to the wiring of the overall routing optimization, it can be broken according to the need to cloth line, and try to re- Wiring to improve overall performance.

The current high-density PCB design has felt that the through-hole is not well adapted, it wastes a lot of valuable wiring channels, in order to solve this problem, there blind hole and buried hole technology. It not only completed the role of through-hole, but also save a lot of wiring channels, so that the wiring process to complete a more fluid, more perfect. PCB board design process is a complex and simple process, in order to master it well, need electronic engineering designers to their own experience, sum up experience.

1, power, ground handling

In the entire PCB design, even if the wiring is done very well, but because the power supply, ground consideration is not thoughtful interference caused by the performance of the product will decline, and sometimes even affect the success rate of the product. So the power, ground wiring to be taken seriously, the power, ground noise generated by the minimum interference to ensure the quality of the product.

For each engineer engaged in the design of electronic products are aware of the noise between the line and the power of the reasons, only to reduce the suppression of noise for the expression. It is well known that a decoupling capacitor is added between the power supply and the ground. As far as possible to widen the power, ground width, preferably ground than the power line width, their relationship is: ground> power line> signal line, usually signal line width: 0.2 ~ 0.3mm, the most fine width 0.05 ~ 0.07mm, the power line is 1.2 ~ 2.5mm, the digital circuit of the PCB can be used to form a wide wire lead wire, that is, to form a ground network to use (analog circuit can not be used to use this) with a large area of ​​copper Line, in the printed circuit board has not been used on the ground are connected with the ground as a ground. Or made of multi-layer board, power, ground each occupied a layer.

2, digital circuit and analog circuit common ground processing

Now there are many PCB board is no longer a single functional circuit (digital or analog circuit), but by the digital circuit and analog circuit mix. So the PCB board design wiring need to consider the interference between them, especially on the ground noise interference. Digital circuit frequency is high, the sensitivity of the analog circuit is strong, the signal line, the high-frequency signal line as far as possible away from the sensitive analog circuit parts, the ground, the entire PCB board only one node, so Must be in the PCB board to deal with the number of internal problems. And in the PCB board internal and analog ground is actually separated, they are not connected between each other, but in the PCB board and the external interface (such as plugs, etc.). Digital and analog to a little short, please note that there is only one connection point. There are also in the PCB board on the ground, which is determined by the system design.

3, the signal line in the electrical (ground) layer

In the multi-layer PCB board wiring, because the signal line layer is not finished cloth line left is not much, then more layers will cause a waste, but also to increase the production of a certain amount of work, the cost has increased accordingly To solve this contradiction, you can consider wiring in the electrical (ground) layer.

First consider the power layer, followed by the formation. Because it is best to preserve the integrity of the formation.

4, large area conductor connection legs processing

In a large area of ​​the ground (electricity), the commonly used components of the legs connected to the connection legs to deal with the need for comprehensive consideration, the electrical performance, the component legs of the pad and copper surface is better, but the Components of the welding assembly there are some bad risks such as: ① welding needs

High power heater. ② easy to cause virtual solder joints. So taking into account the electrical performance and process needs, made of cross-pad, known as the heat shield (heat shield) commonly known as the thermal pad (Thermal), so that the welding can be too much heat due to cross-section of the potential Greatly reduced. Multi-layer PCB board of the power (ground) layer of the same treatment.

5, PCB board wiring in the role of network systems

In many CAD systems, PCB board routing is based on the network system. Grid is too dense, although the channel has increased, but the pace is too small, the figure of the amount of data is too large, which must have a higher storage requirements of the equipment, but also the object of computer electronic products operating speed Great influence. And some passages are ineffective, such as those occupied by the pads of the component legs or by the holes, which are occupied by the holes. The grid is too sparse, the passage of too little impact on the cloth rate. So there must be a dense and reasonable grid system to support the wiring.

The distance between the feet of the standard component is 0.1 inch (2.54 mm), so the basis of the grid system is generally set to 0.1 inches (2.54 mm) or less than 0.1 inches integer multiple of 0.05 inches, 0.025 inches, 0.02 inches, etc. The

6, design rules check (DRC)

PCB board wiring design is completed, it is necessary to carefully check the wiring design is in line with the rules developed by the designer, but also need to confirm whether the rules set to meet the needs of PCB production process, the general inspection has the following aspects:

(1) Whether the distance between the wire and the wire, the wire and the element pad, the wire and the through hole, the element pad and the through hole, the through hole and the through hole are reasonable, and whether the production requirement is satisfied.

(2) whether the width of the power cord and the ground wire is appropriate, whether the power supply and the ground are tightly coupled (low wave impedance), and whether there is a place where the ground wire is widened.

(3) whether the best signal line for the key measures, such as the shortest length, plus protection lines, input lines and output lines are clearly separated.

(4) analog circuit and digital circuit part, whether there is a separate ground.

(5) after the graphics in the PCB board (such as icon, marked) will cause the signal short circuit. Modify some of the unsatisfactory lines.

(6) whether the PCB board with a process line, solder resistance is in line with the requirements of the production process, resistance welding size is appropriate, whether the character mark on the device pad, so as not to affect the quality of electronic equipment.

(7) multi-layer PCB board in the power of the edge of the outer edge of the frame is reduced, such as power supply layer of copper foil exposed outside the board easily lead to short circuit.