| There are a large number and variety of electrical connection structures in a circuit system,such as connectors,solder joints,bonding wires.With the development of electronic science,the signal frequency transmitted by electrical connection structures is higher and higher,and the wavelength of the corresponding electromagnetic wave is shorter and shorter.In many cases,the wavelength and the physical size of connection structures are in an order of magnitude,or even smaller than the physical size of connecting structures,which results in the electrical and electromagnetic characteristics of electrical connection structures very complex.In addition,these electrical connection structures are one of the most easily damaged parts of circuits,which may deteriorate or even fail under environmental stresses.In engineering applications,a seemingly inconspicuous electrical connection fault may lead to 5a huge circuit system failure.Accordingly,the influence of electrical connection fault on the electrical performance of circuits under environmental stresses has attracted extensive attention in academia and industry.In the current work,three dimensional numerical calculation model simulations,equivalent circuit model simulations,mathematical model calculations,experimental measurements are used to investigate the effect of electrical connection faults in high speed circuits and electronic packaging on signal integrity.The main contents include:the influence of electrical contact degradation on digital waveforms and the study of signal integrity improvement methods,the influence of high speed connector degradation on signal transmission,the influence of bonding wire failure on signal transmission and the impedance compensation method in bonding area,the influence of plating materials on electrical and mechanical properties of circuits and intelligent diagnostic methods for electrical connection faults.The main research work and innovations of this dissertation are as follows:1.The effect of electrical contact degradation on wide-band digital signal was analyzed using both the theoretical analysis and experimental testing.The characteristics of digital signals with different rise times through connectors with different degradation levels were studied.An equivalent model of the connector with degraded contact surface was developed,which were validated experimentally.The influence of capacitance characteristics caused by degraded contact surface on digital signal waveform was calculated and analyzed.In addition,based on the degradation characteristics of the connector electrical contact surface,the differential transmission method was applied to enhance signal integrity in such degraded electrical contact circuit.The differential signal waveforms and eye diagrams of high-speed channels with undegraded and degraded connectors were studied.The improvement of the circuit reliability by differential transmission was demonstrated from the perspectives of both experimental investigation and analysis using probability calculations.2.The effect of electrical contact degradation on signal integrity was investigated using model analysis and experimental testing from the perspective of frequency domain.A 3D electromagnetic field model of a high-speed channel with a degraded contact surface was developed to evaluate loss,reflection and crosstalk.Using multiconductor transmission line theory and contact physics,a distributed parameter circuit model of a high-speed channel with degraded contact surfaces was also developed.Both the electromagnetic field model and the circuit model results are validated using experimental tests.In addition,considering the influence of signal transmission,reflection and crosstalk on differential circuit symmetry,the d parameter was defined for measuring the circuit symmetry.The impact of high-speed connector degradation on symmetry of differential circuits was studied by both experimental investigation and electromagnetic numerical calculation model analysis.3.The impact of bonding wire failure on signal transmission was studied using model simulation and experimental testing.The effects of bonding wire failure on both the DC and high frequency characteristics were analyzed.Signal reflection and loss caused by failed bonding wire at different positions and numbers of failed gold bonding wire were also investigated.A 3D electromagnetic field numerical calculation model and a distributed parameter circuit model were developed.The results obtained by the model simulation are validated using experimental tests.In addition,an impedance compensation technique using a chip capacitor for bonding area was introduced.The electrical performance was improved significantly in the frequency band below 4 GHz.In order to expand the operating frequency of the circuit,another compensation approach based on adding a ground conductor was also studied,which can increase the optimized frequency to 18 GHz.The results obtained from the model simulation for both strategies were also validated experimentally.4.The effect of silver migration on signal transmission of printed circuit board was evaluated using both experimental testing and theoretical model analysis.Based on multi-conductor transmission line theory and electrical properties of dendrite like electrochemical migrated silver,a distributed parameter circuit model for the circuit board with silver migration was developed.The correctness of the model was verified by experiments.In addition,the impact of gold plating processes for bonding pads on interconnection quality was studied using model analysis and experimental testing.Printed circuit boards were manufactured using both electroless nickel immersion gold process and electroplating soft gold process.The thickness and roughness of gold plating layer of circuit boards were measured.For circuit boards with different gold plating processes,a finite element analysis model of connection area was developed.the deformations and von-Mises stresses at the interfaces between bonding points and gold-plated layers under tensile force were calculated and analyzed.The maximum tensile breaking force and qualified rate of ball-wedge bonding wires were analyzed from the perspectives of both thickness and roughness of gold plating layer.In addition,the bonding wire failure modes were also observed and analyzed.5.Intelligent detection methods for electrical connection faults were studied.Specifically,the fault characteristics of connectors,bonding wires and solder balls in the frequency domain were analyzed.The reflection and transmission parameters of an example filter circuit with electrical connection faults were calculated using the circuit simulation software.With these obtained electrical parameters,three machine learning algorithms were used to detect example electrical connection faults for the example circuit.Based upon the performance evaluations of the three algorithms,one can conclude that machine-learning-based intelligent fault detection is a promising technique in diagnosing circuit faults due to electrical connection issues with high accuracy and lower time cost as compared to current manual processes. |
