- Jul 07.2018, 16:21:06
How to improve your routing technique?
The routing is greatly important in PCB layout, and it’s worth learning and searching how to make an effective and quick routing to make your PCB routing fantastic.
1、Digital and analog circuit common grounding treatment
Now there are no longer single function circuit( digital and analog circuit), but it’s made up of digital and analog circuits. So it needs to take the mutual interference into consideration as routing, especially the noise interference on the ground. The high frequency of digital circuit, high sensitivity of analog circuit, high frequency signal line is away from the sensitive analog circuit component as far as possible for signal line, but for the ground, PCB is only one bonding to the outside world, so it needs to deal with the problem of digital and analog common ground in the PCB inner, in fact digital ground is not connected with the analog but only at the interface between PCB and outside world. You should pay attention there is only a bonding between digital and analog ground. And others are not common ground on PCB depending on system layout.
2、Signal routing is on the electric layer
It can take routing into consideration on the electric layer to deal with the problem, which more layers will lead to wasting, mass workload to PCB fabrication and high cost when multilayer printed circuit board routing because there is little routing in the signal layer. So taking power plane into consideration firstly, and then the ground. Because it will be better to keep the integrity of ground.
3、The treatment of connecting pins in extensive conductors
It needs to take the treatment of connecting pins into consideration as the normal components’ pins connect with extensive ground, for electric property, it’s better for the pad of component pins to connect with the copper surface, but there are some advantages for soldering assembly of components, such as soldering is with high power heater, and it’s east to pseudo soldering. Making the heat shield, known as thermal to meet the demands of electric property and process, which will reduce the possibility of pseudo soldering that resulting from excessive heat dissipation for section. And the ground pins of multilayer board is treating the same as the components pins.
4、Network system’s function in routing
Routing is made of network system in many CAD systems. It will have a great demand on the storage apparatus and make a great effect on the operation speed of electronic products as grid is too dense, slow step and mass data volume in the map field. However some paths are not effective, such as the pad of component pins, mounting hole and toaling hole and so on. It will make a great effect on routability as grid is shrinkage and less path. So taking a reasonable grid system to be routing with 0.1 inch or less, such as 0.05inch, 0.025inch, 0.02inch and so on.
5、the treatment of power source and ground
It will make an effect on the yield ratio of fabrication and property with the interference resulting from ill-considered power source and ground despite the routing does a good job in PCB. So be strict with the routing of power source and ground, reducing the noise interference minimum to make sure the fabrication quality. Learning the reasons of noise between the ground and power source for every designers, so we make an introduction about reducing the noise: as we know, using decoupling capacitance between ground and power source. Trying to broaden the width of ground and power source and it will be better if the ground is widen than power source as they have the connection of ground＞power source＞signal line, in general, the width of signal line is 0.2～0.3mm, the best is up to 0.05～0.07mm, the ground is 1.2～2.5 mm. It can make an return circuit with wide ground for digital circuit.
It needs to check the routing whether meets the designers’ demands and the rule whether meets PCB process’s demands or not after the routing layout, there are some aspects for the normal checking: the range whether is reasonable and meets the fabrication’s demands or not between wire and wire, wire and components pad, wire and through hole, through hole and through hole. The width of power source and ground whether is reasonable or not, is tight coupling between power source and ground? Whether the great place to broaden the ground or not in PCB. Whether takes the best measures for the key signal line, such as the shortest length, using protective wire and so on. Whether there is a single ground between analog and digital circuit. Whether leading to signal short for the pattern of PCB. Whether solder mask meets PCB fabrication process demands, is the dimension of solder mask reasonable, whether the silkscreen remark is pressing on the pad,avoiding affecting the assembly quality.
The layout of via
Via is one of the important components of multilayer circuit board, and the cost of drilling accounts for 30%-40% of PCB fabrication cost. In short, every hole of PCB can be known as via. There are two kinds of via from the function: one is used for electrical connection in the layer, another is for fixing or positioning of the component. But there are three types of via if based on PCB fabrication process, what is blind via, buried via and through via.
Blind via is located on the top and bottom surface of printed circuit board with a certain depth, which is used for bonding between surface circuit and bottom inner circuit, and the depth of hole is usually less than the aperture. Buried hole, a connecting hole in the inner printed circuit board that gets to the surface of circuit board. The blind and buried hole are in the inner of circuit board, taking advantage of through hole molding process to be finished before laminating, and it may be overlapped several inner layers during the via of being fabrication. Another via is through via, which is through the circuit board, used for interconnecting or mounting the toaling hole as component. The through hole is easy to do in the process and the cost of through hole is lower, so there are so many printed circuit boards using it rather than blind or buried hole. Taking the through hole into consideration if without any special cases.