The Impact And Improvement Of Soldering Connector On Signal Integrity For High-frequency Cable

Soldering connector is the commonly used device in communication cable.It connects with cable by soldering.The technology and quality of soldering have a direct effect on signal integrity.Especially,with the increase of transmission rate and signal frequency,signal integrity problem has become more serious and difficult to solve.Therefore,this thesis focused on soldering connector which will lead to the instability of transmission signal.Regarding soldering between connector and cable as our research object,kinds of methods to reduce the influence on signal integrity will be studied.The main contents are as follows:1.Based on the fundamental theory of signal transmission line and signal integrity,the thesis analyzes the relation between transmission cable electric parameters and signal integrity.According the above theory,we found that the integrity is mainly affected by the conductor cross-sectional area and material conductivity when the signal transmits at resistance-capacitance characteristic region.Together with it,when soldering connector is for the use of high frequency signal,the ratio of conductive skin depth and effective radius of conductor will produce signal loss as a hollow cable with large resistance.Based on the above conclusions and the key points of soldering art,it is found that the major influence factors of signal non-integrity are connector structure,soldering method and soldering materials.It will lead to the impedance change of cross-sectional area,electrical conductivity and effective radius on the soldered dot.In addition,improper operation of soldering,such as the flux of volatile,metal surface oxidation,will cause capacitive change on the soldered dot from micro-hole,fissure and intermetallic compound layer growth.So,one corresponding capacitor model was proposed to get the relationship between capacitive loss and soldering quality problem.2.By using 3D High Frequency Structure Simulator(HFSS)software,different kinds of soldering structures,e.g.,solder cup,square contact or circular contact,were studied by the usage of equivalent circuit model.Where,lap soldering and wire-wrapped soldering were also considered.The impact on signal integrity with soldering material was simulated by setting different resistivity of soldering materials.At the same time,the equivalent capacitor model with the factors of micro-hole size,micro-hole number and micro-hole position was presented to study the impact of signal return loss.Three results have been obtained as follows by simulation.The first one is that the wire-wrapped soldering can be used for circular contact connector,which shows the low return loss with high-frequency signal from 1GHz to 13.35 GHz.As the signal frequency increased from 13.35 GHz to 20 GHz,lap soldering should be selected.Where,the solder cup structure will be preferred to protect the signal integrity.Secondly,the soldering material with Model 63Sn-37 Pb,which is composed of 63% of tin and 37% of lead,should be chosen due to its lower resistivity in comparison with other soldering materials.Finally,we found that the size,number and position of the micro-holes in the soldered dot will influence signal integrity meanwhile.3.More than 130 standard high frequency cables with 0.56 mm of wire diameter and 5mm of length have been fabricated.Where,pair of SMA connectors was soldered for each cable.According to combination of soldering types and connector structures,four catalogues have been designed,which are circular contact with wire-wrapped soldering,square contact with wire-wrapped soldering,square contact with lap soldering,and solder cup with lap soldering.We fabricated 10 samples for each catalogue with 40 cables in total.By the way,we fabricated another 40 cables for the catalogue of solder cup with lap soldering,where,4 kinds of soldering materials,such as,Model 63Sn-37 Pb,Model 90Sn-10 Pb,Model 30Sn-70 Pb,Model 10Sn-90 Pb,were compared with 10 samples for each kind of material.Together with above studies,there are over 50 samples were also fabricated for the catalogue of solder cup with lap soldering to study the effect of micro-hole in the soldering dot.At last,more than ninety solder cables were picked from above 130 sample cables for the performance measurement experimentally.S-parameters,time-jitter and harmonic component on the frequency band from 2G to 20 GHz were studied in the test.The theory analysis and simulation on the signal integrity have been verified by test results.Further,some improvement of soldering based on material selection and soldering fabrication process were proposed.The above study of research achievement has been used for those real cable products in national spacecraft and satellite system.