| With people’s continuous pursuit of intelligence and convenience in life,the specifications of electronic products in the electronic industry are constantly miniaturized,and the volume and spacing of solder joints are also constantly shrinking.At the same time,the usage environment is also becoming increasingly complex and harsh.The hydrothermal environment is one of the important reasons for solder joint failure,and small corrosion defects may cause overall equipment paralysis,so the corrosion of solder joints caused by hydrothermal conditions must be considered in evaluating the reliability of solder joints.This article investigates the surface,microstructure,and performance changes of three commonly used soldering materials and solder joints,Sn-37 Pb,Sn-58 Bi,and Sn-3.0Ag-0.5Cu,through hydrothermal aging experiment,XPS,XRD,electrochemical testing,and shear testing to evaluate their reliability.Firstly,after aging at 85 ℃/85% relative humidity,the surfaces of the three soldering alloys exhibited varying degrees of oxidation and discoloration,and the surface roughness showed an increasing trend.After comparison,it was found that the variation in roughness of Sn-37 Pb was the largest,followed by Sn-3.0Ag-0.5Cu and Sn-58 Bi.The hydroxide content of Sn in the oxide film of Sn-37 Pb and Sn-3.0Ag-0.5Cu soldering materials is greater than the oxide content of Sn,while the content of the two components in Sn-58 Bi is basically the same.At the same time,it was found that Pb on the surface of the solder is more prone to oxidation than Sn,Bi is more prone to oxidation than Sn,and the eutectic structure areas in Sn-3.0Ag-0.5Cu are more prone to oxidation than β-Sn.After hydrothermal aging,the hardness values of Sn-37 Pb and Sn-3.0Ag-0.5Cu soldering alloys decreased with the increase of hydrothermal aging time,while the hardness values of Sn-58 Bi soldering alloys increased with time.Among them,the hardness change of Sn-37 Pb is the largest,followed by Sn-58 Bi,and the change of Sn-3.0Ag-0.5Cu is the smallest.Secondly,electrochemical testing experiments were conducted on three types of soldering materials that underwent different time periods of hydrothermal aging.85 ℃/85%relative humidity had little effect on the corrosion potential of Sn-58 Bi solder,but the dense oxide film generated by the environment on the surface of the solder reduced the thermodynamic corrosion tendency of Sn-37 Pb and Sn-3.0Ag-0.5Cu solder for a certain period of time.However,excessive hydrothermal aging had the opposite effect and exacerbated the corrosion tendency of the solder.85 ℃/85% relative humidity caused the corrosion current density of the three types of soldering materials to decrease and then increased overall due to the first densification and then destruction of the oxide film on the surface.This improved the corrosion resistance of the soldering material surface for a certain period of time,but prolonged hydrothermal aging will weaken their corrosion resistance.The corrosion resistance of the solder was evaluated from other perspectives such as electrochemical impedance spectroscopy and equivalent circuit fitting,and the results obtained were consistent with the polarization curve results.It can be seen that the 85 ℃/85%relative humidity environment has a significant impact on the electrochemical performance of the solder.Finally,the effect of aging in two different hydrothermal environments on the solder joints of three types of soldering materials was studied.Their IMC layer morphology has changed from scallop-shaped to flat,and their thickness and growth rate were not affected by humidity.The influence of 85 ℃/85% relative humidity on the shear performance of solder joints was greater than that of 85 ℃/20% relative humidity.There was no difference in the maximum shear force of solder joints between the two hydrothermal environments in the early stage.85 ℃/20% relative humidity environment had little effect on the plastic brittleness of solder joints,but the effect of 85 ℃/85% relative humidity improved the plasticity of solder joints.However,long-term high humidity hydrothermal environment in the later stage caused local corrosion defects at the bottom corner of the solder joint.Compared to low humidity hydrothermal aging,it greatly reduced the maximum shear force and plasticity of the solder joint,deteriorated its reliability. |
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