Browsing by Author "Liu, Shenyi"

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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.
Low-temperature die attach for power components: Cu-Sn-In solid-liquid interdiffusion bonding
(2022) Emadi, F.; Liu, Shenyi; Klami, Anton; Tiwary, N.; Vuorinen, V.; Paulasto-Krockel, M.
A4 Artikkeli konferenssijulkaisussa
Based on the finite element (FE) simulations done in this work, lowering the bonding temperature significantly decreases the bonding induced residual stresses. Therefore, low temperature Cu-Sn-In SLID process was utilized to bond Si to Si and Si to sapphire under various bonding conditions. The microstructural evolution and the (thermo-) mechanical properties of the joints were studied. The results showed that the Cu-Sn-In SLID bonds composed of a single Cu6(Sn, In)5 IMC phase with high joint strength. Furthermore, the hardness and Young's modulus of Cu6(Sn, In)5 formed in the SLID bonding were measured to be slightly higher than that of binary Cu6Sn5.
Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability
(2024) Emadi, Fahimeh; Vuorinen, Vesa; Liu, Shenyi; Paulasto-Krockel, Mervi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
To meet the essential demands for high-performance microelectromechanical system (MEMS) integration, this study developed a novel Cu-Sn-based solid-liquid interdiffusion (SLID) interconnect solution. The study utilized a metallization stack incorporating a Co layer to interact with low-temperature Cu-Sn-In SLID. Since Cu6(Sn,In)5 forms at a lower temperature than other phases in the Cu-Sn-In SLID system, the goal was to produce single-phase (Cu,Co)6(Sn,In)5 interconnects. Bonding conditions were established for the Cu-Sn-In/Co system and the Cu-Sn/Co system as a reference. Thorough assessments of their thermomechanical reliability were conducted through high-temperature storage (HTS), thermal shock (TS), and tensile tests. The Cu-Sn-In/Co system emerged as a reliable low-temperature solution with the following key attributes: 1) a reduced bonding temperature of 200 °C compared to the nearly 300 °C required for Cu-Sn SLID interconnects to achieve stable phases in the interconnect bondline; 2) the absence of the Cu3Sn phase and resulting void-free interconnects; and 3) high thermomechanical reliability with tensile strengths exceeding the minimum requirements outlined in the MIL-STD-883 method 2027.2, particularly following the HTS test at 150 °C for 1000 h.