Papers by Keyword: Kirkendall Voids

Abstract: This work presents experimental and computational research on the influence of hot isostatic pressing (HIP) of CMSX-4, a second-generation single-crystal nickel-based superalloy, on interdiffusion behavior and the formation of Kirkendall voids in subsequently assembled diffusion couples under isothermal annealing. Two sets of Ni/CMSX-4 diffusion couples were prepared: one using CMSX-4 that had undergone HIP treatment, and the other using CMSX-4 in the as-cast condition. The diffusion couples were annealed at 1250 °C for 144 h. Experimentally measured interdiffusion profiles of all alloying elements, together with synchrotron X-ray 3D μ-tomography of Kirkendall voids, were compared with calculated diffusion profiles and phase-field simulations of void evolution. A direct comparison between the simulation and experimental results enables an explanation of the HIP effect on the density, distribution, and size of the voids, as well as on the observed shifts in the interdiffusion profiles.

Abstract: Kirkendall voids have always been a reliability issue in recent wire bonding technologies in semiconductor package using gold and copper wires. The unpredictable manifestation of these voids has paved the way for a lot of process improvements, parameter optimizations, and material improvements, aiming to alleviate the formation of voids. Predicting when these voids would likely to start to manifest themselves will give us an understanding as to how to improve wire bonding at time-zero, especially on the formation of the intermetallic coverage (IMC) at time-zero. Augmenting different levels of ultrasonic (US) energy at wire bonding gave us different IMC morphologies and thickness at time-zero, which were compared and analyzed through statistical analysis and through a mathematical model. The collective data of each US energy for both time-zero and after each thermal aging, showed when will Kirkendall voids would likely to occur on silver-aluminum [Ag-Al] intermetallics, and if these voids are detrimental to the integrity of the wire bond interphase [Ag3Al] or if it’s still acceptable within the device’s projected lifetime. The survival of the device at the 1000th HTS mark, reveals the reliability of using silver wires for automotive devices in the semiconductor industry today. Furthermore, the overall behavior of [Ag-Al] intermetallics in IM layer thickness can be predicted through an optimized set of parameters at time zero, but its overall numerical behavior can be quite different. Nevertheless, it has been proven through this thesis, that the [Ag-Al] intermetallics can survive 1000 hours of HTS, with different US energy level applications at time-zero.

Abstract: The intermetallic compounds (IMCs) layer formed between Sn-0.7Cu-1.0wt.%Si₃N₄ (SC-1.0SN) solder and Cu-substrate were investigated through isothermal solid-state aging. The SC-1.0SN/Cu solder joints were aged at 50°C and 150°C for 24h, 240h, 480h and 720h duration after reflow. The as-soldered joint IMC formed at interface was Cu₆Sn₅. In addition, only Cu₆Sn₅ layer was observed at the interface of the samples aged at low temperature of 50°C although the aging duration was prolonged up to 720h and has begun to increase in thickness. On the other hand, the Cu₃Sn layer was clearly observed in the sample of aged at 150°C up to 240h. However, at least no voids were vividly observed in the 50°C aged samples, while kirkendall voids were clearly found in Cu₃Sn layer of samples aged at 150°C up to 480h of aging time will be discussed further.

Abstract: The study of composition and microstructure of welded joints was performed before and after the diffusion annealing at elevated temperatures for different annealing time. The Kirkendall effect in the Ni/Ni3Al diffusion couples was observed by means of different methods, e.g. using light, scanning electron and atomic force microscopies. The study suitably completes and specifies the morphology features of Kirkendall voids at different evolution stages, i.e. at nucleation, growing and coalescence. Kirkendall voids occurred in the region between the Matano and γ/γ´interface planes. The location of the γ/γ´ interface that moved in the direction of Ni3Al phase during the annealing resulted from the Al concentration profile measured by EDAX. The Matano plane location was determined by means of Boltzmann-Matano’s method using concentration profile data. It was observed that the void size was increasing in the direction from the Matano plane to the γ/γ´ interface. The obtained results were completed by surface topography of Kirkendall voids of slightly etched specimens by atomic force microscopy (AFM).