Reliability and failure mechanism of copper pillar joints under current stressing

Cai, Hongbin; Guo, Jing; Chen, Jian Qiang; Wu, Di; Liu, Zhi-Quan; Zhu, Qing Sheng; Shang, Jian Ku; Zhang, Li; Guo, Hao

doi:10.1007/s10854-015-3410-8

Cited by 22 publications

(7 citation statements)

References 32 publications

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“…𝜀 0 and 𝜂 0 are the unilateral thickness of the initial Cu 3 Sn layer and Cu 6 Sn 5 layer. As shown in Equation (15), the thickness growth of the Cu 3 Sn and Cu 6 Sn 5 layers has no polarity difference, and follows a parabolic curve relationship with the thermal aging time. The parameters M 𝜀 and M 𝜂 can influence the growth rates of the Cu 3 Sn and Cu 6 Sn 5 layers, respectively.…”

Section: Modeling Of Cu 6 Sn 5 and Cu 3 Sn Thickness Growthmentioning

confidence: 99%

“…Equations ( 16) and (17) show the polarity differences caused by the EM effect and can be used for the quantitative characterization of Cu 3 Sn and Cu 6 Sn 5 growth. 𝜌 𝜀 8.9 × 10 −8 Ω m [15] 𝜌 𝜂 17.5 × 10 −8 Ω m [15] 𝜌 Sn 11 × 10 −8 Ω m [15] Z * Cu∕𝜀 26.5 [15] Z * Cu∕𝜂 26.0 [15] Z * Cu∕Sn 2 [15] 2. , respectively. The Cu solubility in solid Sn solder is ≈0.16 wt%.…”

Section: Modeling Of Cu 6 Sn 5 and Cu 3 Sn Thickness Growthmentioning

confidence: 99%

“…The influence of Ni layers with different thicknesses on the growth rates of Cu 6 Sn 5 and Cu 3 Sn were clarified, and it indicated that the ultrathin Ni layer was not an effective diffusion barrier. C. Chen and H. Ma et al [14,15] found that microbump interconnects would not easily influence on the mechanical stress and thermal gradient, however, the Sn solder is more likely to be depleted and even be completely converted into the Cu 3 Sn layer. [16] B. Kwak et al investigated the transition characteristics for the IMCs phase change in Cu pillar/Sn-3.5Ag microbump and calculated the thickness relationship with annealing time before Sn is completely consumed.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Influence of Temperature and Current Stressing on Cu‐Sn Intermetallic Compound Growth Characteristics of Lead‐Free Microbump

Wei

Guo

et al. 2023

Advcd Theory and Sims

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A numerical analysis of the Cu flux on Cu/Sn/Cu is successfully used to establish kinetic models that are verified with reported data. Kinetic models are adopted to discuss the polarity effect of intermetallic compounds (IMCs) growth at different alloying stages. The models reveal that, before Sn solder is depleted during thermal aging, the net thermodiffusion Cu flux in Cu6Sn5 is over three times larger than that in Cu3Sn. While coupling with current stressing, the IMCs thickness increases from parabola‐like curves to a linear‐like relationship. The degree of influence decreases in the order of Cu6Sn5 on anode, Cu6Sn5 on cathode, Cu3Sn on anode, and Cu3Sn on cathode. Electromigration Cu flux in Sn is the critical factor that accelerates the anode's Cu6Sn5 growth, and its influence on the growth rate over 1000 times that on the anode's Cu3Sn. After Sn solder is depleted, Cu6Sn5 gradually converts into Cu3Sn, and its thickness is linearly decreases with square root of annealing time. When coupling with a current density of 1.0 × 105 A cm−2, the thickness ratio of Cu3Sn/Cu6Sn5 reduces from 1:2 to 1:6. Remarkably, irrespective of whether current exists or not, the depletion of Cu6Sn5 always takes much longer than that of Sn solder.

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Section: Modeling Of Cu 6 Sn 5 and Cu 3 Sn Thickness Growthmentioning

confidence: 99%

Section: Modeling Of Cu 6 Sn 5 and Cu 3 Sn Thickness Growthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Influence of Temperature and Current Stressing on Cu‐Sn Intermetallic Compound Growth Characteristics of Lead‐Free Microbump

Wei

Guo

et al. 2023

Advcd Theory and Sims

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“…Research on Cu pillar microbumps has mainly focused on electromigration under constant direct current (DC) without considering the influence of transformation in the current direction. Ma et al investigated the electromigration behavior of Cu pillar microbumps and found that pure Sn solder was susceptible to complete alloying into Cu 6 Sn 5 and Cu 3 Sn layers [ 9 ]. Park et al investigated the electromigration performance of Cu pillar/Ni/Sn-Ag to analyze the potential mechanisms by which Ni layers improve the resistance to electromigration.…”

Section: Introductionmentioning

confidence: 99%

Interfacial Reaction and Electromigration Failure of Cu Pillar/Ni/Sn-Ag/Cu Microbumps under Bidirectional Current Stressing

Chen

Zhao

et al. 2023

Materials

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The electromigration behavior of microbumps is inevitably altered under bidirectional currents. Herein, based on a designed test system, the effect of current direction and time proportion of forward current is investigated on Cu Pillar/Ni/Sn-1.8 Ag/Cu microbumps. Under thermo-electric stressing, microbumps are found to be susceptible to complete alloying to Cu6Sn5 and Cu3Sn. As a Ni layer prevents the contact of the Cu pillar with the solder, Sn atoms mainly react with the Cu pad, and the growth of Cu3Sn is concentrated on the Cu pad sides. With direct current densities of 3.5 × 104 A/cm2 at 125 °C, the dissolution of a Ni layer on the cathode leads to a direct contact reaction between the Cu pillar and the solder, and the consumption of the Cu pillar and the Cu pad shows an obvious polarity difference. However, with a bidirectional current, there is a canceling effect of an atomic electromigration flux. With current densities of 2.5 × 104 A/cm2 at 125 °C, as the time proportion of the forward current approaches 50%, a polarity structural evolution will be hard to detect, and the influence of the chemical flux on Cu-Sn compounds will be more obvious. The mechanical properties of Cu/Sn3.0Ag0.5Cu/Cu are analyzed at 125 °C with direct and bidirectional currents of 1.0 × 104 A/cm2. Compared with high-temperature stressing, the coupled direct currents significantly reduced the mechanical strength of the interconnects, and the Cu-Sn compound layers on the cathode became the vulnerable spot. While under bidirectional currents, as the canceling effect of the electromigration flux intensifies, the interconnect shear strength gradually increases, and the fracture location is no longer concentrated on the cathode sides.

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“…After 500 h with a current density of 29.8 kA cm -2 at 197 o C, a great number of Kirkendall voids were accumulated at Cu/Cu 3 Sn interfaces which lead to the failure. [5] Although these results are abundant , the failure mechanism of "Cu-Sn microbumps" under current stressing is not clear. In this study, Cu 6 Sn 5 microbumps were fabricated and analyzed after electromigration tests.…”

Section: Introductionmentioning

confidence: 99%

Electromigration in microbumps with Cu-Sn intermetallic compounds

Chu

Zhan

Lin

et al. 2016

2016 International Conference on Electronics Packaging (ICEP)

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The electromigration test of the microbump interconnects with Cu/Cu6Sn5/Cu structure is reported in this study. This Cu6Sn5 intermetallic compound layer was singlecrystal like. The diameter of the microbumps in die-to-die stacking was 30 μm. Test vehicles were applied by a current density of 2.2x10 5 A/cm 2 and settled on a hotplate at 150 o C. The resistances of the microbumps were simultaneously monitored by the four point probe during the test procedure. The Cu6Sn5 transformed into Cu3Sn in the early stage and porous Cu3Sn generated in the Cu6Sn5 layer at later stages. The morphology of porous Cu3Sn could be caused by the current direction. The decomposition of Cu6Sn5 into Cu3Sn and Sn occurs during the EM test. The migration of Sn atoms to the periphery of the underbump-metallization was forced by the current stress, which may be the mechanism of the pore formation with the pore volume of 41.4%. More porous Cu3Sn was found in the cathode end which was an evidence of the EM effect. Finite element analysis was used to do some calculation based on theoretical stoichiometry and microstructures in the test results. The resistivity of porous Cu3Sn structure which was about 30 μΩ−cm which was three times larger than that of Cu3Sn. The porous Cu3Sn may threaten the reliability issues of microbumps.

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Reliability and failure mechanism of copper pillar joints under current stressing

Cited by 22 publications

References 32 publications

Influence of Temperature and Current Stressing on Cu‐Sn Intermetallic Compound Growth Characteristics of Lead‐Free Microbump

Influence of Temperature and Current Stressing on Cu‐Sn Intermetallic Compound Growth Characteristics of Lead‐Free Microbump

Interfacial Reaction and Electromigration Failure of Cu Pillar/Ni/Sn-Ag/Cu Microbumps under Bidirectional Current Stressing

Electromigration in microbumps with Cu-Sn intermetallic compounds

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