In the design of PCB Circuit Board, vias are the key structure for connecting different layers of circuits. The rationality of its design has a vital impact on the electrical performance of the entire circuit board. As electronic equipment develops towards high speed, high frequency and miniaturization, optimizing via design to improve electrical performance has become an important research topic in the field of PCB design.
Vias are mainly composed of hole walls and plating inside the holes. The hole wall material is generally insulating epoxy resin, and the plating is usually copper. The size parameters of vias include hole diameter, hole depth, and plate diameter. A smaller hole diameter can reduce the space occupied by the circuit board, but too small may increase the difficulty of processing and reduce reliability. The hole depth is related to the number of layers of the circuit board. Deeper holes may have uneven plating during electroplating, affecting the stability of electrical connections. The plate diameter affects the connection area between the via and the line, and a larger plate diameter can reduce the connection resistance. From the perspective of electrical performance, the parasitic capacitance and inductance of the via are key indicators. The parasitic capacitance will increase with the decrease of the hole diameter and the increase of the plate diameter, which may cause delays and distortions in the transmission process of the signal. Parasitic inductance is related to the length of the hole. Longer vias will produce greater inductance, which is easy to cause signal reflection and attenuation during high-frequency signal transmission.
First, in the selection of aperture, the accuracy requirements and electrical performance requirements of the circuit board should be considered comprehensively. For high-speed signal transmission lines, the aperture can be appropriately increased to reduce parasitic inductance, but it is also necessary to avoid the aperture being too large to affect the density of the circuit board layout. Secondly, optimize the shape of the via, such as using blind or buried vias instead of through holes. Blind vias only connect the surface and inner layers of the circuit board, while buried vias connect different internal layers. Compared with through holes, they are shorter in length, which can effectively reduce parasitic inductance and capacitance and improve signal transmission speed and quality. Furthermore, the arrangement of vias should be reasonably designed to avoid vias being too dense. Dense vias will increase the parasitic parameters of the circuit board and may cause crosstalk between signals. In the design of multi-layer boards, the high-speed signal layer and the via layer should be reasonably distributed to reduce the impact of vias on high-speed signals.
Via design cannot be carried out in isolation and needs to be considered in conjunction with other design links of PCB Circuit Board. For example, when designing wiring, the location of vias should be planned in advance so that the signal lines can transition smoothly, reduce signal bends and mutations, and reduce signal reflections. In coordination with the design of the power layer and the ground layer, ensure that the connection between vias in different layers will not damage the integrity of the power and ground, and avoid problems such as power noise and ground bounce. When selecting PCB boards, the influence of board parameters such as the dielectric constant on the parasitic capacitance of the vias should also be considered, and the appropriate board should be selected to optimize the overall electrical performance. Through close cooperation with all links, the via design can better play the role of improving the electrical performance of the PCB Circuit Board and meet the needs of modern electronic equipment for high-performance PCBs.
