Browsing by Author "Brand, Sebastian"

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Electromigration Reliability of Cu3Sn Microbumps for 3D Heterogeneous Integration
(2024) Tiwary, Nikhilendu; Grosse, Christian; Kögel, Michael; Windemuth, Thilo; Ross, Glenn; Vuorinen, Vesa; Brand, Sebastian; Paulasto-Kröckel, Mervi
A4 Artikkeli konferenssijulkaisussa
3D heterogeneous integration (HI) and advanced packaging (AP) technologies require small volume, high-density interconnects for stacking discrete chips for which the reliability of interconnects becomes crucial. Intermetallic compounds (IMCs) based μbumps have been shown to outperform solder-based μbumps concerning their resistance to electromigration (EM) related failures, which is a key index to assess the interconnect reliability. Cu-Sn solid-liquid interdiffusion (SLID) bonding is an attractive low-cost wafer-level bonding technology for rapid manufacturing of full Cu3Sn IMC μbumps, However, SLID requires melting of Sn during the bonding process which poses risks and design challenges in manufacturing. Due to Sn squeeze-out during the bonding process, Sn melt could react with redistribution layers (RDLs) or metallization layers and form IMCs at undesired locations resulting in early failures thereby compromising the reliability. The Sn-squeeze out issue during bonding is addressed in this work by designing test structures with equal and unequal lateral dimensions of μbumps in the top and bottom wafers. The effects of Sn-squeeze out on the EM resistance and reliability are compared in both designs. Significant improvement in the Sn-squeeze out and corresponding EM resistance was observed in the test structures manufactured with unequal lateral dimensions of μbumps in the top and bottom wafers. FE element simulations were carried out to gain insights and assess the impact of Sn squeeze-out on the reliability and functionality of the Cu3Sn μbumps.
Fatigue Crack Networks in Die-Attach Layers of IGBT Modules Under a Power Cycling Test
(2024) Liu, Shenyi; Vuorinen, Vesa; Liu, Xing; Fredrikson, Olli; Brand, Sebastian; Tiwary, Nikhilendu; Lutz, Josef; Paulasto-Krockel, Mervi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The die-attach layer is a vulnerable structure that is important to the reliability of an insulated-gate bipolar transistor (IGBT) module. A new failure mechanism named fatigue crack network (FCN) has been identified in the central area of the IGBT modules' solder layer. In this article, to investigate the formation mechanism of the FCN, a fast power cycling test (PCT) (current on 0.2 s and current off 0.4 s) was designed and performed on a commercial IGBT module. Subsequently, scanning acoustic microscopy and X-ray imaging were used for nondestructive inspection of the defects of the solder layer. The cross section was based on the nondestructive inspection results. Then, electron backscattered diffraction analysis was carried out on both observed vertical and horizontal cracks. As a result, both networked vertical cracks at the center and horizontal cracks at the edge of the solder layer were detected. The recrystallization occurred during the PCT. The voids and cracks emerged at high-angle grain boundaries. A finite element simulation was performed to understand the driving force of FCN qualitatively. The stress simulation results indicate that under time-dependent multiaxial stress at the center of the solder, the defects nucleated, expanded, and connected vertically to form the FCNs.