The reliability of copper pillar under the coupling of thermal cycling and electric current stressing

Ma, Hui-Cai; Guo, Jingdong; Chen, Jianqiang; Wu, Di; Liu, Zhi-Quan; Zhu, Qing–Ling; Zhang, Li; Guo, Hongyan

doi:10.1007/s10854-016-5038-8

Cited by 14 publications

(1 citation statement)

References 16 publications

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“…It has been widely used in advanced packaging products such as flip-chip, Co-Wos, and microsystems [ 1 , 2 ]. At present, the interconnection height of Cu pillar microbumps does not exceed 100 μm, and the pitch can be reduced to less than 50 μm, significantly improving the chip package I/O density [ 3 , 4 ]. However, the current density applied to microbumps increases dramatically with the reduction of interconnect size, making electromigration failure of interconnects significant.…”

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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