The electromigration induced microstructure evolution and damage in asymmetric Cu/Sn-58Bi/Cu solder interconnects were investigated by in-situ SEM observation, focused ion beam （FIB） microanalysis and finite element...The electromigration induced microstructure evolution and damage in asymmetric Cu/Sn-58Bi/Cu solder interconnects were investigated by in-situ SEM observation, focused ion beam （FIB） microanalysis and finite element （FE） simulation. The SEM results show that the electromigration-induced local degradation of microstructures, i.e., segregation of Bi-rich phase and formation of microcracks, in the asymmetric solder interconnects is much severer than that in the symmetrical ones. FIB-SEM microanalysis reveals that the microregional heterogeneity in electrical resistance along different electron flowing paths is the key factor leading to non-uniform current distribution and the resultant electromigration damage. Theoretical analysis and FE simulation results manifest that the current crowding easily occurs at the local part with smaller resistance in an asymmetric solder interconnect. All results indicate that the asymmetric shape of the solder interconnect brings about the difference of the electrical resistance between the different microregions and further results in the severe electromigration damage.展开更多
This paper presents a 3D homogenized model able to simulate the nonlinear effects generated by the interaction of ultrasonic waves with microcracks.A hexahedral element with one horizontal elliptical crack is construc...This paper presents a 3D homogenized model able to simulate the nonlinear effects generated by the interaction of ultrasonic waves with microcracks.A hexahedral element with one horizontal elliptical crack is constructed as a reference model.The reference model is smeared to be orthotropic but with different moduli in tension and compression to account for stiffness asymmetry due to crack opening and closure.Different from the existing homogenized models that usually simplify the representative volume element as a homogeneous part and require only one constitutive model for the equivalent material of the whole structure,we assign the constitutive relationship of the same reference model to all the finite elements but with random principal material orientations to take randomly oriented microcracks into consideration.In this way,the randomness of distributed microcracks can be considered in the framework of continuum mechanics.In this manner,the experimentally observed nonlinear effects,such as the generation of both even and odd harmonics,can be reproduced.The developed model has been verified for a 3D bar and a 3D plate.Particularly,the influence of crack density on the amplitude of higher harmonics is analyzed.展开更多
Background： High intraocular pressure （IOP） and low central corneal thickness （CCT） are important validated risk factors for glaucoma, and some studies also have suggested that eyes with more deformable corneas m...Background： High intraocular pressure （IOP） and low central corneal thickness （CCT） are important validated risk factors for glaucoma, and some studies also have suggested that eyes with more deformable corneas may be in higher risk of the development and worsening of glaucoma. In the present study, we aimed to evaluate the association between corneal biomechanical parameters and asymmetric visual field （VF） damage using a Corvis-ST device in patients with untreated normal tension glaucoma （NTG）. Methods： In this observational, cross-sectional study, 44 newly diagnosed NTG patients were enrolled. Of these, 31 had asymmetric VF damage, which was defined as a 5-point difference between the eyes according to the Advanced Glaucoma Intervention Study scoring system. Corneal biomechanical parameters were obtained using a Corvis-ST device, such as time from start until the first and second applanation is reached （time A 1 and time A2, respectively）, cord length of the first and second applanation （length A 1 and length A2, respectively）, corneal speed during the first and second applanation （velocity A1 and velocity A2, respectively）, time from start until highest concavity is reached （time HC）, maximum amplitude at the apex of highest concavity （def ampl HC）, distance between the two peaks at highest concavity （peak dist HC）, and central concave curvature at its highest concavity （radius HC）. Results： Time A 1 （7.19 q- 0.28 vs. 7.37 ~ 0.41 ms, P = 0.010）, length A 1 （1.73 [ 1.70-1.76] vs. 1.78 [ 1.76-1.79] mm, P = 0.007）, length A2 （1.58 [1.46-1.70] vs. 1.84 [h76-1.92] mm, P 〈 0.001）, peak dist HC （3.53 [3.08-4.00] vs. 4.33 [3.92-4.74] mm, P = 0.010）, and radius HC （6.20 ± 0.69 vs. 6.59 i h 18 mm, P = 0.032） were significantly lower in the worse eyes than in the better eyes, whereas velocity A 1 and def ampl HC were significantly higher （0.156 [0.149-0.163] vs. 0.145 [0.138-0.152] m/s, P= 0.002 and 1.19 ± 0.13 vs. 1.15 ± 0.13 mm, P = 0.005, re展开更多
基金Project(51275178)supported by the National Natural Science Foundation of ChinaProject(20110172110003)supported by ResearchFund for the Program of Higher Education of China
文摘The electromigration induced microstructure evolution and damage in asymmetric Cu/Sn-58Bi/Cu solder interconnects were investigated by in-situ SEM observation, focused ion beam （FIB） microanalysis and finite element （FE） simulation. The SEM results show that the electromigration-induced local degradation of microstructures, i.e., segregation of Bi-rich phase and formation of microcracks, in the asymmetric solder interconnects is much severer than that in the symmetrical ones. FIB-SEM microanalysis reveals that the microregional heterogeneity in electrical resistance along different electron flowing paths is the key factor leading to non-uniform current distribution and the resultant electromigration damage. Theoretical analysis and FE simulation results manifest that the current crowding easily occurs at the local part with smaller resistance in an asymmetric solder interconnect. All results indicate that the asymmetric shape of the solder interconnect brings about the difference of the electrical resistance between the different microregions and further results in the severe electromigration damage.
基金supported by the National Natural Science Foundation of China (51875277,52175141,and 51921003)Natural Science Foundation of Jiangsu Province (BK20200414 and BK20220133)+3 种基金China Postdoctoral Science Foundation (2021TQ0152 and 2022M711616)the Foundation Strengthening Plan Technology Fund (2019-JCJQ-JJ-337)Jiangsu Funding Program for Excellent Postdoctoral Talent (2022ZB159)a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘This paper presents a 3D homogenized model able to simulate the nonlinear effects generated by the interaction of ultrasonic waves with microcracks.A hexahedral element with one horizontal elliptical crack is constructed as a reference model.The reference model is smeared to be orthotropic but with different moduli in tension and compression to account for stiffness asymmetry due to crack opening and closure.Different from the existing homogenized models that usually simplify the representative volume element as a homogeneous part and require only one constitutive model for the equivalent material of the whole structure,we assign the constitutive relationship of the same reference model to all the finite elements but with random principal material orientations to take randomly oriented microcracks into consideration.In this way,the randomness of distributed microcracks can be considered in the framework of continuum mechanics.In this manner,the experimentally observed nonlinear effects,such as the generation of both even and odd harmonics,can be reproduced.The developed model has been verified for a 3D bar and a 3D plate.Particularly,the influence of crack density on the amplitude of higher harmonics is analyzed.
文摘Background： High intraocular pressure （IOP） and low central corneal thickness （CCT） are important validated risk factors for glaucoma, and some studies also have suggested that eyes with more deformable corneas may be in higher risk of the development and worsening of glaucoma. In the present study, we aimed to evaluate the association between corneal biomechanical parameters and asymmetric visual field （VF） damage using a Corvis-ST device in patients with untreated normal tension glaucoma （NTG）. Methods： In this observational, cross-sectional study, 44 newly diagnosed NTG patients were enrolled. Of these, 31 had asymmetric VF damage, which was defined as a 5-point difference between the eyes according to the Advanced Glaucoma Intervention Study scoring system. Corneal biomechanical parameters were obtained using a Corvis-ST device, such as time from start until the first and second applanation is reached （time A 1 and time A2, respectively）, cord length of the first and second applanation （length A 1 and length A2, respectively）, corneal speed during the first and second applanation （velocity A1 and velocity A2, respectively）, time from start until highest concavity is reached （time HC）, maximum amplitude at the apex of highest concavity （def ampl HC）, distance between the two peaks at highest concavity （peak dist HC）, and central concave curvature at its highest concavity （radius HC）. Results： Time A 1 （7.19 q- 0.28 vs. 7.37 ~ 0.41 ms, P = 0.010）, length A 1 （1.73 [ 1.70-1.76] vs. 1.78 [ 1.76-1.79] mm, P = 0.007）, length A2 （1.58 [1.46-1.70] vs. 1.84 [h76-1.92] mm, P 〈 0.001）, peak dist HC （3.53 [3.08-4.00] vs. 4.33 [3.92-4.74] mm, P = 0.010）, and radius HC （6.20 ± 0.69 vs. 6.59 i h 18 mm, P = 0.032） were significantly lower in the worse eyes than in the better eyes, whereas velocity A 1 and def ampl HC were significantly higher （0.156 [0.149-0.163] vs. 0.145 [0.138-0.152] m/s, P= 0.002 and 1.19 ± 0.13 vs. 1.15 ± 0.13 mm, P = 0.005, re
