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.

Bonding wires are widely used in microwave circuits and chip packaging. Exposure to harsh environments may lead to connection failure in these wires. In the present work, the impact of such failures on signal transmission was studied using model analysis and experimental testing. The effects of gold bonding wire failure on both the DC and high frequency characteristics were analyzed. Signal reflection and loss caused by failed gold bonding wire at different positions and numbers of failed gold bonding wire were also investigated. Based on computational electromagnetics and transmission line theory, a 3D electromagnetic field numerical calculation model and a distributed parameter circuit model were developed. The electromagnetic field model results are in good agreements with those obtained from the distributed parameter circuit model. The results obtained by the model simulation are validated using experimental tests. The results of this investigation provide a better understanding of the influence of the position and the number of failed bonding wires on the signal integrity of the circuit and theoretical support for identifying failure features in fault diagnosis.

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.

Passive intermodulation (PIM) interference has a significant impact on the transmission quality of radio frequency (RF) communication systems. Coaxial connectors are one of the main nonlinear sources that cause PIM interference in communication systems. In addition, the degradation of connectors caused by multiple insertions and withdrawals, and vibration tends to degrade the PIM performance. In this current work, the mechanism of the influence of these factors on PIM was analyzed. A polynomial model was developed based on the tunneling effect in order to describe the PIM performance of coaxial connectors with various levels of degradation caused by multiple insertions and withdrawals, and vibration. A series of two-tone PIM tests on pristine connectors and degraded connectors were conducted. The test results show good agreement with the model results. This work serves to provide a theoretical basis for evaluating the impact of these factors on the PIM performance of coaxial connectors.

Passive intermodulation (PIM) in radio frequency (RF) pathways can arise from multiple factors, including the passive nonlinear effects inherent in coaxial connectors. This study develops models to characterize PIM behaviors under both ideal and nonideal contact conditions, specifically addressing the scenarios of oblique and shallow insertions. Finite element analysis (FEA) was employed to construct models that assess the current density distribution at the contact interfaces, considering both transverse and axial cross sections of the central conductors. In the transverse cross section, the contact radius is determined by the applied pressure, whereas in the axial cross section, the contact length correlates with the insertion depth. A PIM model was derived based on the peak current density at a localized contact area (a-spot). Customized connector samples were utilized for PIM testing. The consistency between predictions and measurements, confirmed through repeated insertions and withdrawals, substantiates the instability of PIM arising from nonideal connections within the connectors.

Ball-grid array (BGA) packages are widely used in digital signal devices, whose reliability and signal integrity are critical. In this research, the impact of failed ground solder balls on digital signal waveforms was theoretically modeled and analyzed, and the results were experimentally verified. A 3-D electromagnetic field model of a digital signal transmission channel with failed ground solder balls was developed to analyze the signal transmission in the frequency domain. In addition, a time-domain waveform simulation system was developed to examine the changes in the digital signal waveforms before and after degradation. Based on the structural and signal transmission characteristics of the solder area with failed ground solder balls, an equivalent circuit model of the degraded solder area was developed, which accurately predicts the effect of the failed ground solder balls on the amplitude and rising edge of the digital signals. The results obtained from the simulation were validated using experimental tests. This study fully examines the effects of the location and number of failed ground solder ball on signal transmission in both the frequency and the time domain. It provides insight and guidance regarding the impact on signal integrity of such faults, which serves to assist in improved packaging reliability and the development of fault detection strategies for such electronic systems.