Showing papers by "Ming Li published in 2007"

Preparation and characterization of a titanium-substituted hydroxyapatite photocatalyst

Abstract: Nanocrystals of titanium-substituted hydroxyapatite (CTHAp) were prepared with Ti4+ concentrations of x = 0, 0.1, 0.2 and 0.5 [x = Ti/(Ca + Ti)] at hydrothermal temperatures of 100, 150, 190 and 230 °C. The effects of reaction temperature and titanium concentration on the crystal were investigated by using TEM, XRD, FTIR, ICP and XPS. The obtained CTHAp crystallites were rod like pure hydroxyapatite phase (about 70 nm in length and 10 nm in diameter), the crystallinity and grain sizes decreased with the increase of XTi, and increased with hydrothermal temperature from 100 to 230 °C. The concentration of Ti4+ near the surface is larger than in the bulk. The photocatalytic activity of CTHAp was examined by using decomposition of methylene blue (MB) and found that CTHAp had good photocatalytic activity under visible light and UV irradiation.

A new covered stent designed for intracranial vasculature: application in the management of pseudoaneurysms of the cranial internal carotid artery.

Abstract: BACKGROUND AND PURPOSE: The management of intracranial pseudoaneurysms is controversial. The purpose of this study was to provide a preliminary evaluation of the clinical efficacy of a Willis covered stent specially designed for the intracranial vasculature in the management of a pseudoaneurysm of the cranial internal carotid artery (CICA). MATERIALS AND METHODS: Eight patients with pseudoaneurysms of the CICA were treated with use of the Willis covered stent. The flexibility of the entire stent system was gauged from the resistance met when reaching the target lesion and was categorized as no resistance, no apparent resistance, or resistance that could be overcome. The apposition of the Willis stent after deployment was scored as excellent with no endoleak, good with a small endoleak, or bad with an apparent endoleak. Follow-up angiography was performed 3 to 12 months after placement of the stent, and angiographic assessments were categorized as endoleak, stenosis of the covered segment of vessel, or occlusion of parent arteries. Follow-up clinical evaluations were also performed, and outcomes were graded as full recovery, improvement, unchanged, and aggravation. RESULTS: Endovascular treatment was technically successful in all aneurysms without procedural-related complications, and all of the stents were easily navigated to the targeted lesions in the CICA. Complete resolution of the pseudoaneurysm was observed in 6 patients immediately after the procedure, and a minimal endoleak into the aneurysm persisted in 2 patients. No morbidity or mortality and no technical adverse event occurred. A follow-up angiogram confirmed complete reconstruction of the internal carotid artery, with no recurrent aneurysmal filling and no occurrence of stenosis in the area of the stent. By the final follow-up visit, 4 patients had fully recovered, 3 had improved, and 1 patient9s condition was unchanged. CONCLUSION: On the basis of our preliminary experience, the Willis covered stent specially designed for the intracranial vasculature can manage a CICA pseudoaneurysm safely and effectively, but longer follow-up and expanded clinical trials are needed.

Study on the Adhesion Between Epoxy Molding Compound and Nanocone-Arrayed Pd Preplated Leadframes

Abstract: Since Au is used as the end finish on Pd preplated leadframes (Pd PPFs), the weak adhesion between the surface noble metal Au and the epoxy molding compound (EMC) often causes delamination and reduces the reliability of integrated circuit (IC) packages, which greatly limits the application of Pd PPFs. This paper reports on a novel application of arrays of nanocones prepared by a special electrodeposition method to improve the adhesion between the leadframe and EMC. Nanocone-arrayed structures greatly increase the area of the interface between the Pd PPF and the EMC. Shearing strength tests indicate that the adhesion between the EMC and nanocone-arrayed PPF is three to four times higher than that of the conventional PPF. Apart from increased interfacial area, the effect of a physical inlay may also increase the adhesion strength.

Effect of Aging on the Interfacial Reaction between Sn-9Zn-xCr Solder and Cu Substrate

Abstract: Lhe influences of adding 0.05, 0.1, 0.3, 0.5 wt.% Cr to Sn-9Zn alloy on growth of intermetallic compound layer (IMCs) at the interface of Sn-9Zn-xCr/Cu was investigated during aging treatment at 85degC and relative humidity from 20% to 85% for 100 h, 200 h, 350 h, 500 h. Lhe results show that IMCs thickness of Sn-9Zn-Cr alloys is much thinner than that of Sn-9Zn alloy after aging, but there is little difference on IMCs thicknesses among Sn-9Zn-Cr alloys. It is of interest to note that IMCs growth rate of Sn-9Zn-Cr is about 1/4 times of that of Sn-9Zn alloy. We supposed the reason is that Cr can slow down diffusion rate of Zn in solder. It is quite reasonable to consider that reliability of Sn-9Zn-Cr solder joints is better than that of Sn-9Zn solder joints because of thinner intermetallic compound layer.

Oxidation failure of Lead Frame Copper alloys with Surface Electroplated Pure Cu

Abstract: Influence of surface electroplated pure copper on oxidation failure of lead frame copper alloys for IC package were investigate. Pure copper layer will benefit the diffusion of copper ion, so the thickness of copper oxide films increase but the velocity of CuO formation decrease and the oxidation only occurs at pure copper layer. As electroplating pure copper layer on copper alloy exceed a critical thickness, surface electroplating treatment can improve copper alloy's resistance against oxidation failure greatly. The oxide film structure of copper alloys is CuO/Cu2O/Cu substrate, after electroplate treated, and the oxide film structure change to CuO (no or trace)/Cu2O/Cu. The oxide films with only Cu2O have higher adhesion strengths.

Electrodeposition of Palladium Film on Electroless Ni-P Coatings Supported by Si Substrate

Abstract: A transition layer of Ni-P coating will help enhance the hydrogen sensing stability of Pd films supported by silicon wafers. In this work, Pd films were electrodeposited on electroless Ni-P coated silicon wafers. The effect of deposition parameters on the microstructure (especially the morphology) of Ni-P coatings and Pd films were investigated. Experimental results indicated that a lower pH value of electroless plating solution and a longer electroless plating time could increase the size of Ni-P nodular particles. In addition, the morphology of Pd films was shaped by the nanostructures of the Ni-P coating. An optimized Pd/Ni-P structures is expected to present good hydrogen sensing performance.

Properties and Reliability of Sn-Pb and Lead-free Mixed Soldering

Abstract: During the transition from Sn-Pb solder to lead-free solder, it is inevitable to encounter the reliability difficulties when lead-free and Sn-Pb materials were used within the same mounting process. To solve the problem in the mixed soldering, two methods were adopted that is improving the soldering temperature and electroplating Sn-Pb on the surface of the devices then soldering in a lower temperature. Mechanical strength of the solder joint, fracture morphology and the intermetallic compound (IMC) at the interface between solder and board materials were investigated. The experimental results showed the inclination of pores evolving when improving the solder temperature reduces the reliability. However, symmetrical solder joint with high reliability was obtained in the second method.

Preparation and Properties of Sn-9Zn-3Bi-Cr Based Lead-free Solder

Abstract: The influence of different Cr content on oxidation resistance, thermal properties, wetting properties, growth of intermetallic compound of Sn-9Zn-3Bi based solder are described herein, and compare with eutectic Sn-9Zn solder. Cr element segregates in the near-surface layer, and improves the oxidation resistance which contributes to better wettability at the meantime. Sn-9Zn-3Bi-0.3Cr solder shows the best oxidation resistance and wetting properties, followed by Sn-9Zn-3Bi-0.1Cr solder. Because of its small amount, Cr addition causes little change in solidus and liquidus temperature of Sn-9Zn-3Bi alloy. Micrographs of Sn-9Zn-3Bi-xCr/Cu interfaces indicate that the addition of Cr can obviously restrain growth of IMCs, and Sn-9Zn-3Bi-0.3Cr alloy has the thinnest thickness of IMCs.

Field Emission Properties of Ni Nanocones Arrays Fabricated by Electrodeposition

Abstract: Ni nanocones field emission arrays (FEAs) were fabricated by electro deposition. Morphologies of the Ni nanocone arrays were investigated by scanning electron microscope (SEM). Field emission properties of these arrays were tested by a vacuum field emission measurement system. The Ni nanocone arrays had low turn-on fields of 5-6.7 V/mum (corresponding to an emission current of 1 muA) and large currents of 155~206 muA. The effects of nanocones size and alignment on field emission properties indicated that maybe the sharper the nanocones, the better the performance of Ni FEAs. It was shown that morphology of Ni FEAs is a significant important condition and should be studied further.

Preparation of Microcones Array Material for Microelectronic Package

Abstract: Microcones arrays of cobalt were prepared by electrodeposition with special crystallization conditioning agent. The influence of electrodepositing conditions and form factor effect on the morphology of microcones array is reported. X-ray diffraction result indicated that the Co arrays growing with (110) preferred orientation. The Co array had an obvious magnetic anisotropy. The coercive and saturation field perpendicular and parallel to the surface of Co were FE-SEM, XRD and VSM, respectively.