Sn-Bi-X solders are widely used in electronic packaging industry.However,thermomigration(TM)behaviors of Sn-BiX solder joints and the orientations change of Bi grains under the temperature gradient are rarely reported...Sn-Bi-X solders are widely used in electronic packaging industry.However,thermomigration(TM)behaviors of Sn-BiX solder joints and the orientations change of Bi grains under the temperature gradient are rarely reported.In this study,Sn-Bi57-Ag0.7/Cu solder joints were used to conduct a TM test under a temperature gradient of 625℃/cm for 400 h,and an isothermal aging test at 85℃was also conducted for comparison.The microstructural evolution of Sn-Bi-X solder joints after reflow,TM and isothermal aging were analyzed by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electron probe microanalysis(EPMA).The results indicated that the Sn/Bi areal ratio after TM did not change significantly whether at the hot end(from 46.78%/52.12%to 50.90%/48.78%)or at the cold end(from 50.25%/49.64%to 48.71%/51.16%)compared with that of as-reflowed samples due to the insufficient thermal energy.The thickness of intermetallic compound(IMC)after TM at hot end(2.49μm)was very close to that of the IMC at cold end(2.52μm),which was also close to that of the aged samples.In addition,the preferred orientations of Sn and Bi grains in different Sn–Bi–Ag solder joints resulting from different conditions(reflow,TM and isothermal aging)were characterized by electron backscatter diffraction(EBSD).The obtained results demonstrated that both Sn and Bi grains had no preferred orientation whether after reflowor isothermal aging,while the orientation of Bi grains of the sample after TM changed from random direction to c-axis([0001]direction)parallel to the heat flow.Ag 3 Sn could hinder the change of orientation of Bi grains under the temperature gradient,and the corresponding mechanism was also systematically illuminated.This study firstly revealed the orientation change of Bi grains under the temperature gradient,which would have a profound guiding significance for enhancing the reliabilities of Sn–Bi–Ag solder joints.展开更多
Transient liquid phase(TLP)bonding is a potential high-temperature(HT)electron packaging technology that is used inthe interconnection of wide band-gap semiconductors.This study focused on the mechanism of intermetall...Transient liquid phase(TLP)bonding is a potential high-temperature(HT)electron packaging technology that is used inthe interconnection of wide band-gap semiconductors.This study focused on the mechanism of intermetallic compounds(IMCs)evolution in Ag/Sn TLP soldering at different temperatures.Experimental results indicated that morphologies of Ag3Sn grains mainlywere scallop-type,and some other shapes such as prism,needle,hollow column,sheet and wire of Ag3Sn grains were also observed,which was resulted from their anisotropic growths.However,the scallop-type Ag3Sn layer turned into more planar with prolongingsoldering time,due to grain coarsening and anisotropic mass flow of Ag atoms from substrate.Furthermore,a great amount ofnano-Ag3Sn particles were found on the surfaces of Ag3Sn grains,which were formed in Ag-rich areas of the molten Sn and adsorbedby the Ag3Sn grains during solidification process.Growth kinetics of the Ag3Sn IMCs in TLP soldering followed a parabolicrelationship with soldering time,and the growth rate constants of250,280and320°C were calculated as5.83×10-15m2/s,7.83×10-15m2/s and2.83×10-14m2/s,respectively.Accordingly,the activation energy of the reaction was estimated about58.89kJ/mol.展开更多
The abnormal growth of Ag3Sn inter-metallic compounds in eutectic Sn-3.5% Ag solder was investigated through high-temperature aging treatment. Microstructural evolutions of this solder before and after the aging treat...The abnormal growth of Ag3Sn inter-metallic compounds in eutectic Sn-3.5% Ag solder was investigated through high-temperature aging treatment. Microstructural evolutions of this solder before and after the aging treatment were observed by optical microscopy and scanning electron mi-croscopy. Precise differential thermal analysis was made to study the changes in enthalpies of the solder under different conditions. The results reveal that the water-cooled solder is in metastable thermodynamic state due to the high free energy of Ag3Sn nanoparti-cles, which sporadically distribute in the matrix as second-phase. The second-phase Ag3Sn nanoparti-cles aggregate rapidly and grow to form bulk inter-metallic compounds due to the migration of grain boundary between primary Sn-rich phase and the Ag3Sn nanoparticles during high temperature aging treatment.展开更多
基金partially supported by the National Key R&D Program of China(No.2017YFB0305700)。
文摘Sn-Bi-X solders are widely used in electronic packaging industry.However,thermomigration(TM)behaviors of Sn-BiX solder joints and the orientations change of Bi grains under the temperature gradient are rarely reported.In this study,Sn-Bi57-Ag0.7/Cu solder joints were used to conduct a TM test under a temperature gradient of 625℃/cm for 400 h,and an isothermal aging test at 85℃was also conducted for comparison.The microstructural evolution of Sn-Bi-X solder joints after reflow,TM and isothermal aging were analyzed by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electron probe microanalysis(EPMA).The results indicated that the Sn/Bi areal ratio after TM did not change significantly whether at the hot end(from 46.78%/52.12%to 50.90%/48.78%)or at the cold end(from 50.25%/49.64%to 48.71%/51.16%)compared with that of as-reflowed samples due to the insufficient thermal energy.The thickness of intermetallic compound(IMC)after TM at hot end(2.49μm)was very close to that of the IMC at cold end(2.52μm),which was also close to that of the aged samples.In addition,the preferred orientations of Sn and Bi grains in different Sn–Bi–Ag solder joints resulting from different conditions(reflow,TM and isothermal aging)were characterized by electron backscatter diffraction(EBSD).The obtained results demonstrated that both Sn and Bi grains had no preferred orientation whether after reflowor isothermal aging,while the orientation of Bi grains of the sample after TM changed from random direction to c-axis([0001]direction)parallel to the heat flow.Ag 3 Sn could hinder the change of orientation of Bi grains under the temperature gradient,and the corresponding mechanism was also systematically illuminated.This study firstly revealed the orientation change of Bi grains under the temperature gradient,which would have a profound guiding significance for enhancing the reliabilities of Sn–Bi–Ag solder joints.
基金Project(51375260) supported by the National Natural Science Foundation of China
文摘Transient liquid phase(TLP)bonding is a potential high-temperature(HT)electron packaging technology that is used inthe interconnection of wide band-gap semiconductors.This study focused on the mechanism of intermetallic compounds(IMCs)evolution in Ag/Sn TLP soldering at different temperatures.Experimental results indicated that morphologies of Ag3Sn grains mainlywere scallop-type,and some other shapes such as prism,needle,hollow column,sheet and wire of Ag3Sn grains were also observed,which was resulted from their anisotropic growths.However,the scallop-type Ag3Sn layer turned into more planar with prolongingsoldering time,due to grain coarsening and anisotropic mass flow of Ag atoms from substrate.Furthermore,a great amount ofnano-Ag3Sn particles were found on the surfaces of Ag3Sn grains,which were formed in Ag-rich areas of the molten Sn and adsorbedby the Ag3Sn grains during solidification process.Growth kinetics of the Ag3Sn IMCs in TLP soldering followed a parabolicrelationship with soldering time,and the growth rate constants of250,280and320°C were calculated as5.83×10-15m2/s,7.83×10-15m2/s and2.83×10-14m2/s,respectively.Accordingly,the activation energy of the reaction was estimated about58.89kJ/mol.
基金supported by the National Natural Science Foundation of China(Grant No.50401033)the Liu Hui Applied Mathematics Center of Nankai University and Tianjin University(Grant No.T13).
文摘The abnormal growth of Ag3Sn inter-metallic compounds in eutectic Sn-3.5% Ag solder was investigated through high-temperature aging treatment. Microstructural evolutions of this solder before and after the aging treatment were observed by optical microscopy and scanning electron mi-croscopy. Precise differential thermal analysis was made to study the changes in enthalpies of the solder under different conditions. The results reveal that the water-cooled solder is in metastable thermodynamic state due to the high free energy of Ag3Sn nanoparti-cles, which sporadically distribute in the matrix as second-phase. The second-phase Ag3Sn nanoparti-cles aggregate rapidly and grow to form bulk inter-metallic compounds due to the migration of grain boundary between primary Sn-rich phase and the Ag3Sn nanoparticles during high temperature aging treatment.
