High-frequency PCB design goals are smaller, faster and lower cost. And because the interconnection point is the weakest link in the circuit chain. In the RF design, the electromagnetic properties at the interconnection point are the main problems faced by the engineering design. It is necessary to examine each interconnection point and solve the existing problems. Circuit board system interconnection includes chip-to-circuit board, high-frequency PCB board interconnection and high-frequency PCB and external devices between the three types of signal input / output interconnection.
High-frequency PCB design of the chip and high-frequency PCB interconnect is important to the design, but the chip and high-frequency PCB interconnection of the most important problem is the high interconnection density will lead to high-frequency PCB material to become the basic structure of the restrictions The factors that increase the density of interconnects. This article shares the practical techniques of high frequency PCB design. In terms of high-frequency applications, high-frequency PCB board interconnection for high-frequency PCB design techniques are:
1, the transmission line corner to use 45 ° angle to reduce the return loss;
2, to use the dielectric constant values strictly controlled by the number of layers of high-performance dielectric circuit board. High Frequency PCB This method is advantageous for the effective simulation of the electromagnetic field between the insulating material and the adjacent wiring.
3, to specify the high-precision etching of high-frequency PCB design specifications. Consider the specified line width total error of +/- 0.0007 in., High Frequency PCB Undercut and cross section of the wiring shape and specify the wiring sidewall plating conditions. The overall management of the wiring (wire) geometry and the coating surface is important to address the skin effect associated with microwave frequencies and to achieve these specifications.
4, highlight the pin leads to the presence of tap inductance and parasitic effects, High Frequency PCB to avoid the use of lead components. In high-frequency environments, it is best to use surface-mount SMD components.
5. For signal vias, avoid using the via process (pth) on the sensitive plate, as this process results in lead inductance at the vias. If a through-hole on a 20-layer board is used to connect 1 to 3 layers, the lead inductance is present in layers 4 to 19, and buried holes or back drills are used.
6, to provide a rich ground layer. These ground layers are to be connected using molded holes to prevent the effect of the 3-dimensional electromagnetic field on the circuit board.
7, to choose non-electrolytic nickel plating or gold plating process, do not use HASL method for plating. This type of plating surface can provide a better skin effect for high frequency current. In addition, this high-solderable coating requires fewer leads and helps reduce environmental pollution.
8, High Frequency PCB solder mask layer to prevent the flow of solder paste. However, due to the uncertainty of the thickness and the uncertainty of the dielectric constant properties, covering the surface of the entire plate will lead to changes in the circuit performance in the microstrip design. Generally use solder dam (solderdam) as a solder mask.