Coaxial connectors are one of the main contributors to passive intermodulation (PIM) in radio frequency systems. Such systems exhibit nonlinear characteristics, especially as the transmission power is increased. In this paper, microscopic surface analysis and macroscopic nonlinear models are introduced to provide explanations for PIM characteristics and to make more precise predictions for the third-order and fifth-order intermodulation products (IM3 and IM5) power resulting from n-type connectors. The equivalent circuit models are presented to provide insight into the effects of degradation at the microscopic level. Simulation calculations are performed to explore the resistance and capacitance in the circuit models and the relative contribution of various physical parameters. A full discussion of nonlinear current-voltage models coupled with an original method for solving polynomial coefficients is provided. A series of experiments based on two-tone testing is conducted to measure IM products with the input power from 30 to 44 dBm. The experimental results verify the predictions both in the un-degraded and the degraded conditions. The power-dependence of the PIM features and the effect of contact surface degradation on connectors' performance are observed from the measurements, which are consistent with the theoretical predictions.

As an integrated circuit (IC) package, ball grid arrays (BGA) are widely used in various electronic systems, playing an important role in energy transfer and electrical signal transmission. In general, a signal solder ball is usually surrounded by ground solder balls. Compared with the signal solder ball, some ground solder balls are closer to the corner position of printed circuit boards (PCB), which leads to a higher failure risk for the ground solder balls in harsh environments. In this research, the impact of failed ground solder balls on the signal integrity of BGA packages was investigated using both theoretical analysis and experimental testing. A 3-D electromagnetic field model of a BGA high-frequency transmission channel with failed ground solder balls was developed. The $S_{11}$ and $S_{21}$ parameters before and after degradation were analyzed and discussed. Based on transmission line theory, an equivalent circuit model of a soldering transition section with failed ground solder balls was also developed. It was found that the 3-D electromagnetic field model results were in a good agreement with the high-frequency parameters obtained from the equivalent circuit model. Both the 3-D electromagnetic field model and the circuit model results are validated by experimental tests. This study fully considers the return path discontinuity (RPD) aggravated by failed ground solder balls and provides a better understanding of this effect on signal transmission. It provides theoretical understanding and support for the application of fault detection strategies to electronic systems.

High-speed interconnected channels, including printed circuit boards (PCB) and high-speed connectors, are widely used in digital baseband communication systems. Connector degradation may lead to deterioration of the integrity of digital signals and is one of the major causes of low communication quality. In the present work, the effect of electrical contact degradation on signal integrity was investigated using model analysis and experimental testing. A 3D electromagnetic field model of a high-speed channel with a degraded contact surface was developed to evaluate transmission loss, signal reflection, and crosstalk. Using multi-conductor transmission line theory and contact physics, a distributed parameter circuit model of a high-speed channel with a degraded contact surface was also developed. The electromagnetic field model results are in good agreements with those obtained from the distributed parameter circuit model. Both the electromagnetic field model and the circuit model results are validated using experimental tests. The results of this investigation provide a better understanding of the characteristics of signal transmission through a degraded contact surface in a high-speed channel and theoretical support for identifying failure features in fault diagnosis.