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. To study each interconnection point and solve the existing problems. Circuit board systems include interconnects such as chip-to-board, PCB interconnect, and signal input / output between PCB and external devices. This paper mainly introduces the practical techniques of high-frequency PCB design in PCB board interconnection, and it is believed that this paper will facilitate the future design of PCB.
PCB design and chip interconnection in the design of the chip is important, but the chip and PCB interconnection of the most important problem is the interconnection density is too high will lead to the basic structure of the PCB material to limit the growth of intermittent density factors. This article shares the practical techniques of high frequency PCB design. In terms of high-frequency applications, PCB board interconnection 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 by the number of strictly controlled high-performance dielectric circuit board. 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 the PCB design specifications. Consider the specified line width total error of +/- 0.0007 inches, manage the 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 lead there is a tap inductance and parasitic effects, 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, 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.
The above is for everyone to share the PCB board interconnection high-frequency PCB design skills, hoping to help everyone.