In thermosonic wire bonding, a free air ball (FAB) created by electronic flame-off (EFO) is crucial to a reliable first bond. To reveal the mechanisms of FAB and ripple formation, the dynamic FAB formation process was monitored and analyzed with a high-speed camera and digital data acquisition system. FAB formation was found to occur in four stages: initiation, preheating, melting, and solidification. The FAB formation speed and model depend only on the EFO current. The FAB formation speed can be as high as 90.4 μm/ms at an EFO current of 60 mA. A minimum EFO time is required for FAB formation, which depends on the EFO current. A semiempirical model FAB=ηln[ I ( t - 0.5 tmin )]- c , was developed to describe the relationship between the FAB size and the EFO time at different EFO currents. The ripple formation mechanism was investigated by analyzing the solidification stage images. Transient droplet vibration caused by high-speed rolling-up and skin-forming solidification in the molten gold drop caused by a large temperature gradient are two major factors in ripple formation. This analysis is expected to be useful for understanding the FAB formation mechanism and optimizing the EFO parameters.
Looping is a key technology in modern thermosonic wire bonding. To provide insight into the loop formation mechanism, a variable-length link-spring (VLLS) model is proposed. In this model, the wire segments and moment balance equations at the opening end of the wire are dynamically added during the capillary upward movement stage, to simulate the wire feeding and kink formation process. The complete looping process is analyzed by solving nonlinear equations iteratively and using Newton's method. Using this model, the wire profile evolution process and kink number, position, and deformation during looping are obtained and verified by experimental results. The effects of the upward loop trace parameters (reverse motion and kink height parameters) on the final loop profile are studied. The results show that the VLLS model, which considers the upward loop trace, is more suitable for looping process analysis.
AbstractBackground: The World Health Organization declared the outbreak a public health emergency of international concern (Corona Virus Disease 2019) on January 30th, this study aimed to investigate the epidemiological and clinical characteristics of Corona Virus Disease 2019 in Xiaoshan, Hangzhou, and evaluate scientific basis for disease control and prevention. Methods: A total of 30 patients had been admitted to hospital from Jan 22 to Feb 22, 2020, all of them were laboratory confirmed SARS-Cov-2. Demographic, epidemiological, clinical, laboratory data were collected from Hospital information system and Epidemiological investigation reports. All data was performed by descriptive analysis, Chi-square test or non-parametric Mann-Whitney U test, as appropriate. Two sided p value less than 0.05 was considered statistically significant.Results: 30 patients were enrolled, the median age was 44.5 years (IQR 33.8-52.3) and 17 (56.7%) patients were female, 14 (46.7%) patients were native and had no exposure to Hubei Province. At the time of study submission, only one patient had not been discharged and no patients died during the study. The median hospital stay was 16.0 days (IQR 12.5-20.5) and the median course of disease was 20.5 days (IQR 17.0-23.3). The most common symptoms were fever (66.7%), dry cough (26.7%), and pharyngalgia (23.3%) on first admission. Most patients were generally illness or more mild, but 10 (33.3%) patients received oxygen therapy and 14 (46.7%) patients received hormone therapy during their hospitalization. Almost half of patients showed mild lymphocytopenia and 40% patients had elevated concentrations of CRP in the early stages of COVID-19.Conclusions: Among the 30 patients were confirmed with SARA-Cov-2 infection in Xiaoshan, Hangzhou, most of them had clinical presentation of respiratory tract infection, but the median course of disease was more than 2 weeks. Further systematic prospective studies about COVID-19 should be urgently needed.
Through silicon via (TSV) is an important technology to realize three-dimensional (3D) packaging with lower energy consumption, faster signal transmission rate and smaller packaging size. Voids and seams are usually formed in the TSV filling process and an appropriate numerical model is needed to predict the filling process. A mathematical model is presented and verified by experiments. In the simulation, we found that as the suppressor concentration increases, the cupric ion in the microvias decreases more slowly with increasing microvias depth; the location of the peak of the accelerator surface coverage is further away from the orifice and the microvias can maintain a larger range of high suppressor surface coverage, resulting in a higher filling ratio. In addition, the presence of accelerators cannot change the distribution of cupric ions in the microvias and the suppressor surface coverage. Therefore, the filling ratio is not affected. But the presence of accelerators can greatly accelerate the cupric deposition rate.
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