Papers by Author: Zhi Gang Dong

Abstract: In order to improve the surface quality of sapphire substrates ground by diamond wheel, the chemo-mechanical grinding (CMG) tools for sapphire grinding was investigated in this paper. According to the processing principle of CMG, three CMG tools with different abrasives of SiO2, Fe2O3 and MgO were developed respectively. The compositions of the CMG tools were designed and optimized based on the physicochemical characteristics of sapphire. The grinding experiments were performed with the developed CMG tools and the grinding performance of three kind of tools were evaluated by comparing the surface roughness and the MRR of sapphire. The experiment results show that the grinding performance of SiO2 CMG tool was worst. The surface roughness and MRR corresponding to SiO2 CMG tool were all significantly poorer than Fe2O3 and MgO CMG tools. The highest MRR could be obtained by Fe2O3 CMG tool, but the best surface quality was obtained by MgO CMG tool.

Abstract: Aiming at the problems such as metal ionic contamination, poor dispersion property and low material removal rate (MRR) in the chemical mechanical polishing (CMP) process for sapphire crystal, a proper CMP slurry based on the organic basis was studied in this paper. Through the single-factor experiment, the effect of different abrasives, pH regulators, dispersants and active agents on the surface roughness and material removal rate (MRR) were studied and a fine CMP slurry was developed. The polishing performance of developed CMP slurry was also researched by comparing the MRR and the surface roughness of sapphire crystal with that polished using the KA-901 CMP slurry. The results show that the MRR and the surface roughness corresponding to the developed slurry were all better than KA-901 slurry, and the developed CMP slurry has a good application prospect.

Abstract: The paper reports an experimental study on the effect of honing parameters on the honing surface roughness, material removal rate and surface topography. A cylindrical honing machine was developed, on which the honing experiments for stainless steel cylinder parts were performed with different honing parameters including the abrasives and its grit size of honing stones, honing pressure and honing time. The results can provide helpful instruction to the determination of the honing process and parameters.

Abstract: Scratch experiments were performed on MgO (001) plane along different crystallographic orientations with the gradually increased forces to investigate the deformaton and damage of MgO. The normal and lateral forces during scratch, as well as the topography characteristics of the residual scratch along different crystallographic orientations were compared and analyzed. The cracks propagation around the scratch were studied. The patterns of cracks and scratches were found to be very different when scratching along different crystallographic orientations. The mechanism of cracks forming beside the scratches on single crystal MgO was discussed.

Abstract: The intermetallics of Cu6Sn5 that are formed at the Sn-based solder/ Cu substrate interface play a significant role in solder joint reliability. The characterization of the mechanical properties of the interface Cu6Sn5 is essential to understand the mechanical performance and structural integrity of the solder joints. In this study, the interface Cu6Sn5 and (Cu,Ni)6Sn5 formed in Sn-Cu and Sn-Cu-Ni ball grid array (BGA) joints were investigated using nanoindentation. The results demonstrated that the strain rate sensitivity and the activation volume of these intermetallics were affected by the reflow times and load conditions. The strain rate sensitivity of Cu6Sn5 and (Cu,Ni)6Sn5 were estimated from 0.023 to 0.105, and the activation volume of Cu6Sn5 and (Cu,Ni)6Sn5 were estimated from 0.128 b3 to 0.624 b3 (b=4.2062x10-9 m) for 1, 2 and 4-reflowed Sn-Cu (-Ni) samples.

Abstract: Nanoindentation tests with the aid of acoustic emission monitoring were performed on single crystal MgO (001) plane to investigate the deformation of MgO under high indentation pressures. The results indicated that the deformation of MgO under nanoindentation with a sharp indenter could be classified into three stages: elastic deformation, elastoplastic deformation, and fragmentation. The elastic energy release and fracture occurred could be identified using acoustic emission signals.

Abstract: Single crystal MgO can be used as the substrates to deposit HTS films. The subsurface damage (SSD) generated in processing has great effect on the strength and performance of the substrates. However, the characteristics of MgO SSD and its formation mechanism have not been understood fully. In this paper, the surface and subsurface damage caused by saw cutting, rough lapping and fine lapping of MgO substrates were studied by cross-section of microscopy and SEM. The formation mechanism was discussed; and a SSD model was presented.