Effect Of Polyvinyl Chloride Smoke On Corrosion Behavior Of Typical Tin Solder

As an electronic packaging material,tin solder plays an important role in the reliability of electronic equipment.With the miniaturization and high integration of electronic equipment,the corrosion of the solder joints has become more serious,and the failure of electronic products has also become more serious.With the prohibition of leaded solders,lead-free solders,such as Sn-Cu,Sn-Ag,Sn-Ag-Cu,have been widely developed and applied,and the reliability issues has gradually received widespread attention.The popularization and rapid development of electricity have led to more frequent fires caused by electrical failures.Polyvinyl chloride and polyethylene are used as wire and cable insulation raw materials in various scenarios in our daily life.Once a fire occurs,it is easy to burn and generate fire smoke.At locations far away from the fire site,the fire could cause non-thermal damage to equipment such as smoke corrosion.At present,there are few reports on the influence of smoke on the corrosion of tin solder at home and abroad.Therefore,this article aims to investigate the corrosion behavior of four kind typical tin solders,Sn-0.7Cu,Sn-3.0Ag,Sn-3.0Ag-0.5Cu,and Sn-37 Pb under the polyvinyl chloride smoke atmosphere.The effects of factors such as smoke concentration,ambient temperature and relative humidity were studied respectively.The corrosion kinetics model of typical tin solder under the atmosphere of polyvinyl chloride smoke was established,and the corrosion microstructure and change law were analyzed.In addition,the corrosion products were analyzed to reveal the corrosion mechanism.Besides,the reliability of the ball grid array package with Sn-3.0Ag-0.5Cu solder under different concentrations of polyvinyl chloride smoke atmosphere was studied,and the electrical failure mode and corrosion morphology were analyzed.(1)Effect of smoke components on the long-term corrosion behavior of tin solders.The weight loss method was used to comparatively study the corrosion dynamic parameters such as mass loss and corrosion rate of halogen-containing polyvinyl chloride material and halogen-free polyethylene material on the Sn-3.0Ag-0.5Cu solder for 15 days.The field emission scanning electron microscope was used to analyze the corrosion microstructure of the solder surface.The energy spectrometer,Xray diffractometer and X-ray photoelectron spectrometer were used to analyze the corrosion product composition.The research results show that Sn-3.0Ag-0.5Cu solder has no obvious corrosion under polyethylene smoke?atmosphere and is severely corroded under polyvinyl chloride smoke atmosphere,which can divided into two stages:the corrosion rate decreased exponentially at a rapid rate during smoke deposition,and the corrosion rate decreased exponentially at a slower rate in the complete stage of fire deposition.Sn-3.0Ag-0.5Cu solder has a lot of flaky corrosion products under the polyvinyl chloride smoke atmosphere,which gradually becomes larger with the increase of corrosion time,and then becomes smaller and thicker,and continues to increase;the corrosion products are mainly Sn21 Cl 16(OH)14O6,SnO and SnO2.However,individual flaky corrosion products could be seen until 15 days under the polyethylene smoke atmosphere,which are mainly SnO and SnO2.In addition,the corrosive polyvinyl chloride smoke atmosphere was selected to study the long-term corrosion behavior of Sn-0.7Cu,Sn-3.0Ag and Sn-37 Pb solders.The research results show that the mass loss and corrosion rate of the three kinds of tin solder exhibit the same exponential change trend as the Sn-3.0Ag-0.5Cu solder in the smoke deposition stage and the complete deposition stage.The flaky corrosion products of Sn-0.7Cu solder and the flaky and fibrous corrosion products of Sn-37 Pb solder gradually become larger with the increase of corrosion time;the change trend of flake corrosion products of Sn-3.0Ag solder with corrosion time is consistent with Sn-3.0Ag-0.5Cu solder.The corrosion products of Sn-0.7Cu and Sn-3.0Ag solder is consistent with those of Sn-3.0Ag-0.5Cu solder,while the flaky corrosion product of Sn-37 Pb solder is consistent with it,but the fibrous corrosion product is PbCl2.(2)Effect of smo(2)Effect of smoke concentrations on the corrosion behavior of tin solders.Four different concentrations of polyvinyl chloride fire smoke from 20 g/m3 to 140 g/m3 were selected to study its influence on the corrosion behavior of four typical tin solders.The research results show that corrosion degree of the four kinds of tin solders is more serious with the increase of the smoke concentration.When the smoke concentration is low,the smoke concentration has a greater influence on the degree of corrosion change for the tin solders.Sn-37 Pb solder is the most corrosion resistant,followed by Sn-0.7Cu solder,and Sn-3.0Ag-0.5Cu solder shows the poorest corrosion resistant.The corrosion products of the four tin solders all become larger with the increase of the smoke concentration.The corrosion of Sn-37 Pb solder is an electrochemical reaction in which the tin-rich phase and the lead-rich phase are dissolved as the anode,while the corrosion of lead-free solders is an electrochemical reaction in which the tin-rich phase is dissolved as the anode.Oxygen absorption and hydrogen evolution reactions occur in all four kinds of tin solder cathodes.The most corrosion resistance of Sn-37 Pb solder is shown because the PbCl2 formed on the surface is insoluble and can inhibit the dissolution of the tin-rich phase;while Sn-3.0Ag-0.5Cu solder is the poorest corrosion resistance because the surface area of the intermetallic compound as the cathode is greater than the other two lead-free solders.((3)Effect of ambient temperature and relative humidity on the corrosion behavior of tin solders.Ambient temperature and relative humidity of 10~50? and50% RH~90% RH were selected to study its influence on the corrosion behavior of four typical tin solders unde polyvinyl chloride smoke atmosphere.The research results show that at 10~50?,the corrosion of the four typical tin solders become severe as the ambient temperature rises;the corrosion products become larger.In the range of50%RH~90%RH,the corrosion degree of the four typical tin solders become serious with the increase of environmental relative humidity,while at 98%RH,the corrosion degree has decreased,but it is still higher than those at 80% RH;The corrosion products and corrosion kinetics showed a consistent trend.The corrosion products of four tin solders are consistent under different temperature and humidity environments:lead-free solder corrosion products are mainly Sn21Cl16(OH)14O6,SnO and SnO2,while Sn-37 Pb solder corrosion products contain another PbCl2.The results shows that external environmental factors couldn't affect the composition of corrosion products on tin solder.(4)Effect of smoke concentrations on the reliability of ball grid array package.The NI data acquisition instrument was used to analyze the reliability of Sn-3.0Ag-0.5Cu ball grid array packaged in different concentrations of polyvinyl chloride flue gas.The research results show that under 20 g/m3 smoke atmosphere,the resistance of the daisy chain circuit increases slowly with the corrosion time,and the surface of the solder ball is slightly corroded.As the smoke concentration increases,the daisy chain circuit short-circuits as soon as it is exposed to the smoke atmosphere,the resistance decreases,and then the resistance increases slowly.In the high-concentration 140 g/m3 smoke atmosphere,a secondary short circuit occurred in the peripheral channel due to the settlement of a large amount of smoke pollutant.In addition,the leakage current is first detected between the open circuits at about 16.5h,indicating a short circuit occurs.Therefore,the ball grid array package composed of Sn-3.0Ag-0.5Cu solder doesn't appear open circuit failure,but mainly in short-circuit failure mode.