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Start Over Author "Li, Junhui" Publisher institute of electrical and electronics engineers (ieee)
59 results on '"Li, Junhui"'

28. Robustness Investigation on Nanosized-Scandia-Doped Dispenser Cathodes

Author

Pan Zhaoliu, Yunfei Yang, Yiman Wang, Jinshu Wang, Wei Liu, and Li Junhui

Subjects
Materials science, business.industry, 020502 materials, Doping, 02 engineering and technology, Electron, 021001 nanoscience & nanotechnology, Temperature measurement, Cathode, Electronic, Optical and Magnetic Materials, Anode, law.invention, Semiconductor, 0205 materials engineering, law, Optoelectronics, Electrical and Electronic Engineering, 0210 nano-technology, business, Current density, Order of magnitude
Abstract

In order for practical applications in vacuum electron devices, the robustness of scandia-doped dispenser (SDD) cathode is a major concern. Emission properties after air exposure and gas poisoning have, therefore, been studied. A full restoring of emission has been proved after the cathodes were exposed to air and reactivated for a time much shorter than initial activation. Poisoning experiments demonstrated that the poisoning pressure thresholds of residual gases for the SDD cathode are about half to one order of magnitude higher at equivalent temperatures but with higher emission level in comparison with that of an excellent M cathode. The cathode is easier to recover after poisoning and can operate stably in a nonideal environment. These features are thought to be related to the surface Ba–Sc–O structure which has closely chemical association, better stability for air exposure, relatively high tolerance to gas poisoning, and the semiconductor emission characteristic.

Published
2018

43. Effects of Ultrasonic Power and Time on Bonding Strength and Interfacial Atomic Diffusion During Thermosonic Flip–Chip Bonding

Author

Liu Linggang, Han Lei, Deng Luhua, Li Junhui, and Zhang Xiaolong

Subjects
Materials science, Scanning electron microscope, Analytical chemistry, Thermocompression bonding, Industrial and Manufacturing Engineering, Electronic, Optical and Magnetic Materials, Atomic diffusion, Anodic bonding, Shear strength, Ultrasonic sensor, Electrical and Electronic Engineering, Deformation (engineering), Composite material, Flip chip
Abstract

In this paper, bonding strength of thermosonic flip-chip (FC) bonding was tested by a Dage 4000 bonding tester, atomic diffusion of bonding interfaces was detected by a scanning transmission electron microscope, and deformation of the bumps was observed by X-ray inspection system. Experimental results show that moderate ultrasonic power (about 4 W) results in higher shear strength of FC interfaces, while excessively high ultrasonic power induces larger displacement of vibration to damage bonding performance. Appropriate ultrasonic bonding time (about 100 ms) leads to the optimal thickness of atomic diffusion at the interfaces (about 200 nm) and better bonding bump shear strength with an average of 75 g. Overlong ultrasonic bonding time obviously aggravates the deformation of the bumps, which reduces bonding precision, thickens the thickness of atomic diffusion at the interfaces and damages the bonding strength. So, optimized parameters of ultrasonic power of 4 W and ultrasonic bonding time of 100 ms are proposed to improve the quality and performance of FC bonding.

Published
2012

49. Dynamics Features of Cu-Wire Bonding During Overhang Bonding Process

Author

Deng Luhua, Han Lei, Ma Bangke, Liu Linggang, and Li Junhui

Subjects
Bonding process, Wire bonding, Lead bonding, Materials science, chemistry, Deflection (engineering), Bonding strength, Aluminium, Metallurgy, chemistry.chemical_element, Electrical and Electronic Engineering, Indentation hardness, Electronic, Optical and Magnetic Materials
Abstract

Cu-wire overhang bonding process is investigated first by a high-speed camera system. It was found that the greater impact, rebound, and deflection of overhang die during the Cu-wire bonding process happen since a hard Cu ball hits with the die with a 1.0-μm-thick Al pad, which affects the bonding strength. When the thickness of the Al pad on the die increases to 2.8 μm, its microhardness is three times lower than that of the 1.0-μm Al pad, which will help to improve the dynamics features of hard Cu overhang bonding. Real-time dynamics features prove that the loading process of the 2.8-μm-thick Al pad is much more stable than that of the 1.0-μm-thick Al pad. Furthermore, impact and rebound reduce significantly; thus, the shear strength of Cu-wire overhang bonding increases significantly.

Published
2011

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