Study of Low-Temperature Thermocompression Bonding in Ag-In Solder for Packaging Applications

Low-temperature solders have wide applications in integrated circuits and micro-electromechanical systems packaging. In this article, a study on Ag-In solder for chip-to-chip thermocompression bonding was carried out. The resulting joint consists of AgIn₂ and Ag₉In₄ phases, with the latter phase having a melting temperature higher than 400°C. Complete consumption of In solder into a Ag-rich intermetallic compound is achieved by applying a bond pressure of 1.4 MPa at 180°C for 40 min. We also observe that the bonding pressure effect enables a Ag-rich phase to be formed within a shorter bonding duration (10 min) at a higher pressure of 1.6 MPa. Finally, prolonged aging leads to the formation of the final phase of Ag₉In₄ in the bonded joints.     

Enhancement of the thermal stability and mechanical properties of a PMMA/aluminum trihydroxide composite synthesized via bead milling

The use of aluminum trihydroxide (ATH) fillers as non-halogen flame retardants for polymethylmethacrylates (PMMA) creates a conflict between the mechanical properties and heat resistance of the composites. Therefore, to ensure that the PMMA mechanical properties remain satisfactory, improvements in both the filler–polymer interactions and the ability to control the size and size distribution, morphology and dispersion of the fillers are required. Thus, in the present study, bead milling was used to control both the size distribution and dispersion of ATH fillers in MMA, which had an initial average size of 0.75 μm. The dispersion was obtained by alteration of the surface characteristics of ATH fillers using a silane-based dispersing agent, (3-acryloxypropyl) trimethoxysilane (APTMS). Bead milling successfully comminuted the ATH particles and prevented the formation of ATH agglomerates. The smallest average size of the ATH particles after bead milling was 300 nm. Highly dispersed ATH filler particles were observed in the TEM images of the PMMA/ATH composites. The filler–polymer interaction, i.e. the interaction parameter (B), was calculated. The effects of volume fraction, particle size distribution, and surface modification of the fillers on the results of dynamic mechanical analysis (DMA) are discussed. The thermal stability of the PMMA/ATH composites was also investigated using thermal gravimetric analysis (TGA).     

Performance analysis of the SOFC–MGT hybrid system with gasified biomass fuel

Analysis of electricity generation efficiency of the biomass SOFC–MGT hybrid system has been made for several cases of different composition of fuel relevant to typical air-, oxygen- and steam-blown biomass gasification processes. Reference case for comparison is the one where pure methane is used as fuel. In the analysis, multi-stage model for internal reforming SOFC module developed previously has been used with some modification. It is found that efficiency achieved for all the three cases of different types for biomass fuel is reasonably high and so that the biomass SOFC–MGT hybrid system is promising. However, in all the three cases, efficiency is lower than the counterpart of pure methane case, both in the SOFC module and in the hybrid system. Among the biomass fuel cases, efficiency is found to be highest with steam-blown biomass fuel both for the SOFC module and for the hybrid system. The lowest efficiency is found in the case of air-blown fuel. In addition, effects of higher steam content in the biomass fuel and variety in composition of biomass fuel for each gasifying agent are also studied.     

Hepatitis B Virus-Like Particle: Targeted Delivery of Plasmid Expressing Short Hairpin RNA for Silencing the Bcl-2 Gene in Cervical Cancer Cells

Gene therapy research has advanced to clinical trials, but it is hampered by unstable nucleic acids packaged inside carriers and there is a lack of specificity towards targeted sites in the body. This study aims to address gene therapy limitations by encapsidating a plasmid synthesizing a short hairpin RNA (shRNA) that targets the anti-apoptotic Bcl-2 gene using truncated hepatitis B core antigen (tHBcAg) virus-like particle (VLP). A shRNA sequence targeting anti-apoptotic Bcl-2 was synthesized and cloned into the pSilencer 2.0-U6 vector. The recombinant plasmid, namely PshRNA, was encapsidated inside tHBcAg VLP and conjugated with folic acid (FA) to produce FA-tHBcAg-PshRNA VLP. Electron microscopy revealed that the FA-tHBcAg-PshRNA VLP has an icosahedral structure that is similar to the unmodified tHBcAg VLP. Delivery of FA-tHBcAg-PshRNA VLP into HeLa cells overexpressing the folate receptor significantly downregulated the expression of anti-apoptotic Bcl-2 at 48 and 72 h post-transfection. The 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay demonstrated that the cells’ viability was significantly reduced from 89.46% at 24 h to 64.52% and 60.63%, respectively, at 48 and 72 h post-transfection. As a conclusion, tHBcAg VLP can be used as a carrier for a receptor-mediated targeted delivery of a therapeutic plasmid encoding shRNA for gene silencing in cancer cells.     

Decolorization of beads-milled TiO2 nanoparticles suspension in an organic solvent

In this paper, a new method is proposed for the decolorization of a yellow-hued suspension of rutile TiO₂ nanoparticles in an organic solvent (diethylene glycol dimethylether). The presence of color has always been undesirable in a suspension of nanoparticles filler used for industrial needs, particularly for optical applications.A colorless suspension was achieved by irradiating well-dispersed TiO₂ nanoparticles in an organic solvent with UV-light (λ = 254 nm) for 5 h. TiO₂ nanoparticles of 1 and 5 wt.% were dispersed using a beads mill method. Trimethoxytrifluor(propyl) silane was used as a dispersant to achieve stability. The effect of the UV-light irradiation on the TiO₂ nanosuspension was investigated by means of a Fourier transform nuclear magnetic resonance analyzer (FT-NMR). The dispersant was partially desorbed due to the interaction of UV light and the TiO₂/dispersant complex. Thus, an enhanced transparency and the absence of color were obtained for well-dispersed TiO₂ nanoparticles in an organic solvent.     

Intramedullary femoral osteosynthesis: an additional cause of ARDS in multiply injured patients?

This study analysed the effects of reaming and intramedullary nailing and thoracic injury related to development of ARDS and multi-organ failure in multiply injured patients. Sixty patients were entered into a retrospective follow-up study. Twenty-one patients with thoracic injury and femoral shaft fracture, treated by intramedullary nailing, were compared with 17 patients with a femoral shaft fracture without thoracic injury, and with 22 patients without femoral shaft fracture but with major thoracic injury. The incidence of ARDS, multiple organ failure (MOF) and the mortality rate in the groups was analysed, using chi 2 and Fisher exact tests. No significant differences in age, sex and ISS existed between the groups. There were no statistically significant differences with regard to the incidence of developing ARDS (P > 0.5), MOF (P > 0.5) and mortality rate (P > 0.2) after injury. The results of this study suggest that reaming of the femoral shaft as part of an intramedullary nailing procedure is not a major cause in developing ARDS and MOF in patients with femoral shaft fractures and thoracic injury. Conventional intramedullary nailing can be considered as a safe procedure in femoral shaft fractures in multiply injured patients, as well as in the presence of major thoracic injury.     

Comparison of Preconditioned Conjugate Gradient Method and LDLT Factorization for Structural Analysis

This paper compares the efficiency of the preconditioned conjugate gradient (PCG) method and the LDL ^T factorization for solving a sparse system of linear equations in large-scale structural analysis with both single- and multiple-load cases. In the PCG method we present an incomplete LDL^T preconditioning method that can be used to efficiently solve a system of linear equations with a wide range of matrix conditions, system sizes, and computer memory limitations. The preconditioning method is very flexible, and we can easily balance the size of the preconditioning matrix and the level of the preconditioning that is appropriate for the problem to be solved. For comparison, we use an implementation of a row-oriented sparse LDL^T solution method.     

Synthesis of polyblends from polypropylene and poly(R,S)‐β‐hydroxybutyrate,and their characterization

Blends of modified polypropylene (PP) with poly(R,S)‐β‐hydroxybutyrate (PHB) were prepared by casting polymer solutions, followed by compression molding into thin films. The modified polypropylene was obtained by oxidation with hydrogen peroxide. Oxidation of polypropylene produced new functional groups such as carbonyl and hydroxyl groups on the polymer chain, and a decrease in molecular weight and crystallinity of the polymers. Maximum crystallinity and mechanical properties of the polyblends were found with a PP/PHB ratio of 90/10 (w/w), and then decreased with increasing PHB content in the polyblends. Biodegradability of the polyblends was lower than that of bacterial and synthetic PHBs. Furthermore, an increase of PHB proportion in the polyblends resulted in highly non‐compatible polyblends. Hence only PHB and small parts of the polyblends were decomposed by microorganisms. Copyright © 2006 Society of Chemical Industry