The wiring is the finest and most limited skill in the PCB design process, and the following are some good wiring skills and Essentials:
First of all, the number of layers of PCB can be divided into single layer, double layer and multi layer, and the single layer is now basically eliminated. Double deck boards are used for many times in the sound system. They are usually used as rough boards for power amplifiers. Multilayer boards refer to 4 storeys or more than 4 storeys. Generally speaking, 4 level is enough for components. From the angle of the hole, it can be divided into holes, blind holes, and burial holes. The through hole is a hole is straight from the top to bottom; the blind hole is from the top or bottom of the hole to the intermediate layer, and then not to wear, the advantage is that the hole location is not from nose to tail, the other layers in the hole position can still walk the line is this; buried hole hole is the middle layer to the middle layer, buried, the surface is completely invisible.
Before automatic routing, we need to interact with the more demanding lines in advance. The input and output side lines should not be adjacent to each other, so as to avoid reflection interference. When necessary, the ground wire can be isolated, and the wiring of the two adjacent layers should be perpendicular to each other, because the parasitic coupling is easily produced in parallel. Automatic routing rate depends on good layout, can be preset routing rules, such as wire bending times, via hole number, the step number etc.. In general, exploratory wiring is adopted first, and the short line is quickly connected. Then through maze routing, the global routing path is optimized, which can disconnect the existing lines and retry the wiring as needed, so as to improve the overall wiring effect.
1, wiring between power and ground wire
(1) the coupling capacitor should be added between the power supply and the ground wire. To power after decoupling capacitor after pin connected to the chip, the figure cited several faulty connection and a correct connection method, we refer to, is not have made such a mistake? General decoupling capacitor has two effects, one is to provide high current moment chip the two is to remove the noise of power, on the one hand is to allow the power supply noise less influence chip, on the other hand is not affected due to the noise of chip power supply.
(2) to widen the power supply and ground wire as far as possible, preferably the ground line is wider than the power line, and its relation is: ground wire > power line > signal line.
(3) a large area of copper can be used as the ground wire, and the places that are not used are connected with the ground on the PCB, for the use of the ground wire, or for the multilayer boards, the power supply and the ground wires occupy one level.
2. Processing of digital and analog circuits
Because of high frequency digital circuit, analog circuit sensitivity, the signal line, the high frequency signal line as much as possible away from the circuit device simulation is sensitive, but for the entire PCB, PCB wire on the outside of the node can have only one, so it must be No. in digital circuit and analog circuit at PCB is the problem, and in the internal circuit board, digital circuit and analog circuit is actually separated, only in the PCB to connect with the outside interface (such as plug etc.). The location of the digital circuit is slightly shorter than that of the analog circuit. Please note that there is only one connection point and there is no common ground on the PCB, which is determined by the system design.
3. Dealing with the corner of the line
Usually the corner of the line will have a change of thickness, but when the diameter of the line changes, there will be some reflection. The angle of the corner is the worst, the right angle is the worst, the 45 degree angle is better, and the corner is the best. But rounded corners are rather troublesome for PCB design, so it's usually decided by the sensitivity of signals. The general signal can be processed at 45 degree angle. Only those very sensitive lines need to use rounded corners.
4, the design rules check after the cloth line
We generally check the following aspects:
(1) is the distance between line and line, line and component pad, line and through hole, component pad and through hole, through hole and through hole reasonable, and whether it meets production requirements.
(2) whether the width of the power cord and ground wire is suitable, whether the power supply is tightly coupled with the ground wire (low wave impedance), is there any place to widen the ground wire in the PCB?
(3) whether the best measures are taken for the key signal lines, such as the shortest length, and the protection line, the input line and the output line are clearly separated.
(4) whether the analog circuit and the digital circuit part have their own independent ground lines.
(5) whether the graphics (such as illustrations and bets) added to the PCB will cause a short circuit of the signal.
(6) to modify some undesirable lines.
(7) whether the process line is added to the PCB, whether the resistance welding is in line with the requirements of the production process, whether the size of the solder joint is suitable, whether the character mark is pressed on the device pad, so as not to affect the quality of the electric equipment.
(8) whether the edge of the outer frame of the power layer in the multi-layer plate is reduced, such as the short circuit of the copper foil out of the power layer.