An optimal design of soldering transition section between SMT RF connector and PCB

Abstract

With the continuous increase of signal transmission rate, the impact of soldering transition section between surface mount technology (SMT) radio frequency (RF) connector and printed circuit board (PCB) on the entire transmission path becomes more and more serious. In this paper, the transmission characteristics of soldering transition section are analyzed by means of scattering matrix, time domain reflectometry (TDR) and other tools in signal integrity analysis, and an equivalent circuit model based on stub lines is established. At the same time, the methods to improve impedance continuity and adjust cutoff frequency are proposed, such as reducing the radius of the pad, cutting out a circle on layer below the pad, biasing the center of circle cutout, increasing the impedance of the pad and the connecting segment of the transmission line, so as to optimize the transmission characteristics of 40-50GHz window. Full-wave simulation results show that these optimization methods can effectively reduce the reflection coefficient and improve the transmission coefficient in the optimization window. The experimental results show that the optimized scheme controls the S11 below -10dB from DC to 50GHz, which is much better than that of -5dB before optimization, and proves the effectiveness of the optimization.