Mechanical characterization of Sn–Ag-based lead-free solders

Recently, preventing environmental pollutions, lead-free (Pb-free) solders are about to replace tin–lead (Sn–Pb) eutectic solders. However, the mechanical properties of Pb-free solders have not been clarified. Hence, the following study was conducted; first, a rate-dependent plasticity was characterized to represent the inelastic deformation behavior for Sn–Ag-based lead-free solders. The material parameters in a constitutive model were determined in a direct method combining both rate-dependent and rate-independent plastic strains. The constitutive model unifies both rate-dependent creep behavior and rate-independent plastic behavior occurring concurrently at the same time in the solders. Secondly, the strength of solders with a variety of plating materials was studied. Intermetallic compounds (IMC) between solder and electrical pads are formed during reflow process and gradually grow in service. By using the Cu-plates on which Cu or Ni or Ni/Au plating was deposited, the specimens of solder joints were fabricated with Sn–Ag-based lead-free solders. After aging the specimens in an isothermal chamber, tensile tests were performed. From scanning electron microscope (SEM) microscope observation and EDX microprobe analysis, the growth and components of the IMC layer were also examined. Based on the experimental tests, the relations between solder joint strength and the aging period were discussed. Furthermore, the validation of fracture strength of solder joints resulting from the tensile tests was verified with package-mounted board level reliability tests.     

Production of two types of ice crystal-controlling proteins in Antarctic bacterium

Pseudomonas fluorescens KUAF-68, which was isolated from Antarctica, had both ice-nucleating protein and antifreeze protein activities in the culture broth. We found that both proteins were separately produced based on the results of column chromatography, SDS-PAGE analysis and Southern hybridization. The activity of the ice-nucleating protein was stimulated by the addition of glycine (0.020 N%), whereas the activity of the antifreeze protein was stimulated by the addition of L-asparagine (0.025 N%). This is the first report on the production of two types of ice crystal-controlling proteins in one bacterial strain.     

Comparison of mechanical properties of PP/SEBS blends at intermediate and high strain rates with SiO2 nanoparticles vs. CaCO3 fillers

The present article focuses on the effect of two types of inorganic fillers (SiO₂ and CaCO₃) on the mechanical properties of PP/SEBS blend. The nominal particle diameters of SiO₂ and CaCO₃ are 7 nm and 1 μm, respectively. The studied blend ratios were PP/SEBS/SiO₂ (CaCO₃) = 75/22/3 and 73/21/6 vol %. The morphology of polymer blends was observed and the distributions of the SEBS, SiO₂, and CaCO₃ particles were analyzed by transmission electron microscopy (TEM). Tensile tests were conducted at nominal strain rates from 3 × 10^?1 to 10² s^?1. The apparent elastic modulus has the local strain‐rate dependency caused by SiO₂ nanoparticles around SEBS particles in the blend of PP/SEBS/SiO₂. The yield stress has weak dependency of morphology. The absorbed strain energy has strong dependency of the location of SiO₂ nanoparticle or CaCO₃ fillers and SEBS particle in the morphology. It is considered that such morphology, in which inorganic nanoparticles are located around SEBS particles, can prevent the brittle fracture while the increased local strain rate can enhance the apparent elastic modulus of the blend at the high strain rate. On the basis of the results of this study, the location and size of inorganic nanoparticles are the most important parameters to increase the elastic modulus without decreasing the material ductility of the blend at both low and high strain rates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Estimation of static strength of adhesively bonded single lap joints with an acrylic adhesive under tensile shear condition based on cohesive zone model

In this study, the tensile shear and bending tests of adhesively bonded single lap joints with the acrylic adhesive was evaluated experimentally and numerically. In the previous paper, the traction-separation laws in mode 1 and mode 2 for an acrylic adhesive were directly obtained from the observation of failure process using Arcan type adhesively bonded specimens: simultaneous measurements of the J-integral and the opening displacements in the directions normal, δ_n and tangential to the adhesive layer, δ_s respectively. The experimental results were compared with numerical simulations conducted in ABAQUS including cohesive damage model. The cohesive laws obtained in the previous paper were simplified to trapezoidal shape from the experimentally obtained ones which were indicated in the previous paper. A good agreement was found between the experimental and numerical results. Then, to investigate the damage evolution in the adhesive layer for some lap joints, microscopic video observation was conducted near the end of the adhesive layer, and the video image have been compared with the contours of damage variable obtained by FEM corresponding to the video images. The observed damage evolution also agrees with the trend of damage variable.     

Considerations on performance evaluation of cavity-backed slotantenna using the FDTD technique

The finite-difference time-domain (FDTD) method is considered a versatile and efficient tool for the solution of Maxwell's equations in complex structures for any time dependence. We show an antenna feed model suitable for performance evaluation of a cavity-backed slot antenna using the FDTD technique. The gap voltage and the coaxial feed models are examined, and their input characteristics and absolute gains are compared. Analytical results show that the input characteristics are estimated with fewer time steps for the coaxial model than for the conventional gap voltage model. Furthermore, we show how to calculate absolute gains and radiation patterns using the coaxial model and a sinusoidal voltage source at the desired frequency. The computed results of the absolute gain converge after the fifteenth period of the voltage source for the coaxial model and are in good agreement with the experimental results. On the other hand, the absolute gain is observed to fluctuate when the gap voltage model is used. The performance evaluation and comparison reveals that the coaxial model is an appropriate feed model for use in the analysis of the performance of the cavity-backed slot antenna using the FDTD technique. The good agreement of the FDTD results with the experimental measurements demonstrates the effectiveness of the model and the method proposed     

Chemothermal pulverization: Crushing titanate crystals to obtain nanosized powders via high-temperature treatment

In this study, we investigated chemothermal pulverization (CTP) phenomena that are induced in titanate single crystals and ceramics by high-temperature treatment at approximately 1000℃ under reactive gas containing ammonia and oxygen and cause these materials to break down into nanosized powders. Structural characterization revealed that there were many nanosized voids formed in titanates during heat treatment for CTP, and subsequent analysis revealed that these voids were filled with nitrogen gas. These results indicated that CTP consisted of four steps: the in-diffusion of nitride ions from the surface to titanates, the deposition of nitrogen molecules (gas) inside the titanate crystals instead of nitride formation, the growth of voids by further nitrogen transport from the surface to voids, and, finally, the breakdown of the walls between voids to form nanopowders. Furthermore, we discussed the exact mechanism of CTP phenomena by examining the effect of doping into titanates on the progress of CTP and by conducting theoretical calculations for the simulation of nitrogen impurities in titanate lattices.     

Heterogeneous expression of nm23 gene product as a predictor of lymph nodal status in human breast cancer

The nm23 gene was originally identified by differential hybridization of metastatic murine melanoma cell lines. Some experimental studies demonstrated a significantly low metastatic potential of melanoma cell lines transfected with the nm23 gene. In this study, we clarified the relationship between intracellular nm23-immunoreactivity and lymph nodal status of human breast cancer. We analyzed 82 surgically removed breast tumors including 67 invasive carcinomas (ductal, lobular and mucinous carcinomas). The nm23 expression was diffusely positive in the benign tumors and non-invasive carcinomas. Of the invasive ductal carcinomas, lymph node metastasis was found in 67.7% (21/31) of the focally positive/negative cases and in 18.2% (4/22) of the diffusely positive cases (p<0.001). Immunohistochemically, advanced margins of invasive carcinomas with lymph node metastasis were shown to be negative for nm23 expression, while intraductal carcinoma components were positive. This observation suggested that focally positive/negative nm23 expression can be a predictor of lymph node metastasis of invasive ductal breast carcinoma.     

A novel evaluation method for interfacial adhesion strength in ductile dissimilar materials

The energy of interface adhesion between two elastic–plastic materials was directly evaluated as the mechanical work supplied exclusively to separate the interface. Interface crack extension was simulated by elastic plastic finite element models, where the nodes along the interface in the vicinity of crack tip were divided into two nodes and the nodal forces were gradually decreased to zero. While further plastic deformation takes place in the volume of materials during crack extension, the work done by these nodal forces against mutual displacement of crack surfaces should be consumed on the surfaces and thus equals to the interface adhesion energy. This technique was applied to a copper/polyimide system for flexible printed circuits in accordance with the new experimental results. In comparison to the results obtained by the conventional peel test, this technique yielded far smaller amount of interface energy successfully excluding the energy dissipated with bulk plastic deformation without any insertion of cohesive strip along the interface in the model.     

Study on an Undershot Cross-Flow Water Turbine

This study aims to develop a water turbine suitable for ultra-low heads in open channels, with the end goal being the effective utilization of unutilized hydroelectric energy in agricultural water channels. We performed tests by applying a cross-flow runner to an open channel as an undershot water turbine while attempting to simplify the structure and eliminate the casing. We experimentally investigated the flow fields and performance of water tur- bines in states where the flow rate was constant for the undershot cross-flow water turbine mentioned above. In addition, we compared existing undershot water turbines with our undershot cross-flow water turbine after at- taching a bottom plate to the runner. From the results, we were able to clarify the following. Although the effec- tive head for cross-flow runners with no bottom plate was lower than those found in existing runners equipped with a bottom plate, the power output is greater in the high rotational speed range because of the high turbine ef- ficiency. Also, the runner with no bottom plate differed from rtmners that had a bottom plate in that no water was being wound up by the blades or retained between the blades, and the former received twice the flow due to the flow-through effect. As a result, the turbine efficiency was greater for runners with no bottom plate in the full ro- tational speed range compared with that found in runners that had a bottom plate.