Vias Design in High Speed PCB Board
We all know that in the high-speed PCB design, vias, which seems very simple, often can bring a great negative effect on the circuit design. So when designing PCB, we should meet the following requirements:
1.Consider from the aspects of cost and signal quality, a reasonable size as the via size is a wise choice. For example, as to a 6~10-layer memory module PCB design, the choice of 10/20 mil (drilling/pad) vias is better. For some high-density small size board, you can try to use 8/18 mil vias, it is difficult to use a smaller size of the vias under the current technical conditions. For vias used for power supply or ground, it is better to use a larger size so as to reduce the impedance.
2.The use of thin PCB is conducive to reducing the two parasitic parameters of vias.
3.Try to keep the signal routing on the same layer as far as possible, that is to say try not to use unnecessary vias.
4.The pins of the power and ground pins should be punched as close as possible, and the shorter the lead between the via and the pin the better, as they may increase the inductance. At the same time, the power and ground leads should be as thick as possible to reduce the impedance.
5.Place some grounded vias near the vias which needs signal exchange layer, so that it can provides singal with the shortest loop. In addition, remember that the process is flexible. The via model has pads on each layer, but we can also reduce or eliminate the pads on some layers. Especially when the via density is very high, it may lead to the formation of a cut-off slot on the copper-plated layer. At this time, in addition to moving the via, we can also consider reducing the via size on the copper-covered pad.