Mixed Assemblies Research Articles

Microstructural Analysis of Reworked Ball Grid Array Assemblies Under Thermomechanical Loading Conditions

Plastic ball grid array packages (Sn3.0Ag0.5Cu) were assembled with Sn3.0Ag0.5Cu and Sn37Pb solder paste to form Pb-free and mixed BGA assemblies. The Pb-free and mixed assemblies were subjected to one (1X) rework cycle and three (3X) rework cycles. All the reworked Pb-free and mixed assemblies were then subjected to a temperature cycling test with a temperature range of -55°C-125°C. The cycles to 0.1% failure of 1X reworked Pb-free assemblies was 18% smaller than that of nonreworked Pb-free assemblies, and the cycles to 0.1% failure of 3X reworked Pb-free assemblies was approximately 100% smaller. However, the cycles to 0.1% failure 1X reworked mixed BGA assemblies was approximately 200% larger than that of the nonreworked mixed BGA assemblies, and the cycles to 0.1% failure 3X reworked mixed assemblies was 35% larger. Detailed microstructural analysis and geometry analysis were provided to explain the temperature cycling reliability differences between the nonreworked and reworked assemblies, as well as the differences between the Pb-free assemblies and the mixed assemblies. The increase in the temperature cycling reliability of reworked mixed assemblies was found to be related to more homogenous Pb-rich phase distribution in the bulk solder.

Microstructural Analysis of Reballed Tin-Lead, Lead-Free, and Mixed Ball Grid Array Assemblies Under Temperature Cycling Test

In this study, ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (SAC305) solder balls were reballed with Sn-37Pb solder balls. Three different reballing methods were used. The non-reballed lead-free BGAs were assembled with SAC305 and Sn-37Pb solder pastes to form the lead-free and mixed assemblies. The reballed Sn-Pb BGAs were assembled with Sn-37Pb solder paste to form the reballed Sn-Pb assemblies. All assemblies were subjected to a temperature cycling test with a temperature range of −55°C to 125°C. For the same component type, the reballed BGA assemblies showed similar temperature cycling reliability regardless of the reballing methods. However, the temperature cycling reliability of the reballed assemblies was worse than that of the mixed and the lead-free assemblies. The mean cycles-to-failure of the mixed assemblies was larger than or equal to that of the lead-free assemblies. Failure analysis revealed that the failure site in reballed Sn-Pb assemblies was located in the bulk solder at the component side regardless of the component type and the reballing method, indicating that the reballing method did not influence the crack propagation in reballed assemblies. The mixed assemblies had the same failure site as the lead-free assemblies, i.e., in the bulk solder at the component side. The microstructure differences between the tin-lead, lead-free, and mixed assemblies are also discussed in detail.

Pebble and Rock Band: Heuristic Resolution of Repeats and Scaffolding in the Velvet Short-Read de Novo Assembler

BackgroundDespite the short length of their reads, micro-read sequencing technologies have shown their usefulness for de novo sequencing. However, especially in eukaryotic genomes, complex repeat patterns are an obstacle to large assemblies.Principal FindingsWe present a novel heuristic algorithm, Pebble, which uses paired-end read information to resolve repeats and scaffold contigs to produce large-scale assemblies. In simulations, we can achieve weighted median scaffold lengths (N50) of above 1 Mbp in Bacteria and above 100 kbp in more complex organisms. Using real datasets we obtained a 96 kbp N50 in Pseudomonas syringae and a unique 147 kbp scaffold of a ferret BAC clone. We also present an efficient algorithm called Rock Band for the resolution of repeats in the case of mixed length assemblies, where different sequencing platforms are combined to obtain a cost-effective assembly.ConclusionsThese algorithms extend the utility of short read only assemblies into large complex genomes. They have been implemented and made available within the open-source Velvet short-read de novo assembler.

Metalloporphyrin Assemblies on Pyridine-Functionalized Titanium Dioxide

Porphyrin adsorption on TiO2 nanoparticles has been achieved for multiple porphyrins, and in mixed porphyrin assemblies, via axial ligation to surface-bound pyridine anchored by either para carboxylic or phosphonic functionalizations. Homogenous assemblies were prepared and characterized, while mixed metalloporphyrin assemblies were demonstrated by controlling the concentration ratios of respective porphyrins in the modifying solution. Evaluation of the assemblies using spectroscopic techniques and electrochemistry confirms high porphyrin retention, while exhibiting their surface bound optical and electrochemical properties. A thorough study is discussed where several metalloporphyrins have been evaluated (Ru(CO)OEP, Ru(CO)TPP, and ZnTPP) for relative comparisons and relationships to pyridyl axial binding strengths. The systematic study evaluates multiple background cases using either H2TPP, TiO2 modification with benzoic acid, or unmodified TiO2 to confirm the high affinity of Ru and Zn porphyrins for surface-anchored pyridyl sites. The simple method of step-by-step coordinative anchoring of porphyrins to TiO2 using small, commercially available molecules is highly adaptable for use in dye-sensitized solar cells (DSSC) where intimate contact between the absorbing dye and the semiconductor is required. DSSC devices with novel mixed porphyrin assemblies were shown to give higher power performance than DSSCs utilizing sensitization with only one type of porphyrin.

Electrochemistry and electrocatalytic properties of mixed assemblies of horseradish peroxidase, poly(diallyl dimethylammonium chloride) and gold nanoparticles on a glassy carbon electrode

Poly(diallyldimethylammonium chloride), gold nanoparticles (Au-NPs; 2–5 nm) and horseradish peroxidase (HRP) were alternately self-assembled on a glassy carbon electrode. Due to the conducting wire effect of the Au-NPs, the HRP undergoes direct electrochemistry with a small peak-to-peak separation of 33 mV and a formal potential of −0.370 V (versus SCE). The reaction involves a single electron transfer coupled to a one-proton transfer reaction. Electrochemical impedance spectroscopy and cyclic voltammetry also were applied to characterize the self-assembly process and to study the electrochemical behavior of the immobilized HRP. Its good electrocatalytic response to the reduction of hydrogen peroxide resulted in a novel third-generation biosensor for this species.

Characterization and Cytotoxicity of Self-Organized Assemblies of Curcumin and Amphiphatic Poly(ethylene glycol)

Polymer-conjugated nanoparticles are an important technology to control the stability, safety, and efficacy in drug delivery systems. Herein, we investigate self-organized mixed assemblies of a lipophilic drug candidate, curcumin (Cm), and a poly(oxyethylene) cholesteryl ether (PEG-Chol). Cm was assembled together with PEG-Chol to form nano-sized assemblies (around 10 nm) of assumed micelles. In contrast with the rapid decomposition of free Cm due to the hydrolysis, the Cm was highly stabilized in the nanoparticles, especially at below 40 mol% Cm. Cell viability assay revealed that the cytotoxic activity of the Cm/PEG-Chol nanoparticles against myeloma cells is higher than those of free Cm in a comparison at 1 microM. On the other hand, both the Cm/PEG-Chol nanoparticles and PEG-Chol micelles had significant cytotoxicity to the myeloma cells at 5 microM. Taken together, the present Cm/PEG-Chol system offers a stable nanoparticle encapsulating Cm which can be injected as a liquid. Cm and vehicle micelles will damage the cancer cells cooperatively.

Self-assembled interpenetrating networks by orthogonal self assembly of surfactants and hydrogelators

Interpenetrating networks (IPN) consist of two or more networks of different components which are entangled on a molecular scale and cannot be separated without breaking at least one of the networks. They are of great technological interest because they allow the blending of two or more otherwise incompatible properties or functions, and furthermore synergistic effects might arise from the simultaneous operation of the two networks. So far, the preparation of interpenetrating network gels by self-assembly approaches was doomed to fail because the conventional polymers and surfactant building blocks either phase separate or form mixed assemblies, respectively. Here we report on self-assembled interpenetrating networks obtained by the orthogonal self-assembly of small molecular hydrogelators and surfactants. Preliminary studies on the self-assembly behaviour and viscoelastic properties of these systems revealed that these self-assembled IPN have a number of intriguing properties. For instance, the presence of two coexisting networks offers new possibilities for compartmentalization, and will allow one to adjust the viscoelastic properties between 'soft' and 'hard' gels. The non-covalent character of such IPN makes their formation fully reversible, which can be exploited for dual responsive systems. Most interestingly, self-assembled IPN can also act as a very primitive, yet unique, model for biological interpenetrating networks like the extracellular matrix and the cytoskeleton, and thereby contribute to our understanding of these very complex systems.

Nanopatterning of donor/acceptor hybrid supramolecular architectures on highly oriented pyrolytic graphite: a scanning tunneling microscopy study.

Hybrid supramolecular architectures have been fabricated with acceptor 1,4-bis(4-pyridylethynyl)-2,3-bis-dodecyloxy-benzene (PBP) and donor 2,6-bis(3,4,5-tris-dodecyloxy-phenyl)dithieno[3,2-b:2',3'-d]thiophene (DTT) compounds on highly oriented pyrolytic graphite (HOPG) surfaces, and their structures and molecular conductance are characterized by scanning tunneling microscopy/spectroscopy (STM/STS). Stable, one-component adlayers of PBP and DTT are also investigated. The coadsorption of two-component mixtures of PBP and DTT results in a variety of hybrid nanopattern architectures that differ from those of their respective one-component surface assemblies. Adjusting the acceptor/donor molar ratio in mixed adlayer assemblies results in dramatic changes in the structure of the hybrid nanopatterns. STS measurements indicate that the HOMO and LUMO energy levels of PBP and DTT on an HOPG surface are relatively insensitive to changes in the hybrid supramolecular architectures. These results provide important insight into the design and fabrication of two-dimensional hybrid supramolecular architectures.

1P-229 長鎖-短鎖リン脂質混合会合体の形態と物理化学的性質(生体膜/人工膜・構造物性,第46回日本生物物理学会年会)

1P-229 長鎖-短鎖リン脂質混合会合体の形態と物理化学的性質(生体膜/人工膜・構造物性,第46回日本生物物理学会年会)

Studies on an Ester-Modified Cationic Amphiphile in Aqueous Systems: Behavior of Binary Solutions and Ternary Mixtures with Conventional Surfactants

The aqueous behavior of an ester-modified cationic amphiphile with the molecular structure CH3CH2O(C=O)(CH2)6(C=O)O(CH2)8N+(CH3)3Br-, in the following referred to as A, has been investigated. Systems with A as the only solute, as well as different aqueous mixtures with conventional cationic surfactants, primarily dodecyltrimethylammonium bromide (DTAB), were included in the study. Isotropic solution samples were characterized using 1H NMR, 13C NMR, NMR diffusometry, and conductivity measurements, whereas liquid crystalline samples were investigated by optical polarization microscopy and small-angle X-ray diffraction. The results are compared to the behavior of the binary system of DTAB and water. A does not exhibit a typical surfactant behavior. When it is present as the only solute in a binary aqueous system, it forms neither conventional micelles nor liquid crystalline phases. However, there is clear evidence that it assembles with lower cooperativity into loose clusters at concentrations above 25-30 mM. When A is mixed with DTAB in solution, the two amphiphiles form mixed assemblies, the structure of which varies with the total amphiphile concentration. In concentrated mixtures with alkyltrimethylammonium surfactants, A can participate in hexagonal liquid crystalline phases even when it constitutes a significant fraction of the total amphiphile content.

Forward and Backward Compatibility of Solder Alloys With Component and Board Finishes

The primary objective of the research presented in this paper is to qualify the reliability of mixed assemblies by comparing them to the conventional Sn-Pb assembly and completely Pb-free assembly. The research investigates both forward and backward compatibility in electronic assemblies using a design of experiments (DOE) approach. The investigation utilized a test vehicle containing an area array component (BGA169) and chip components (0603 resistors). Hot air solder leveling (HASL) and organic solderability preservative (OSP) surface finishes were used on the test vehicles to represent Sn-Pb and Pb-free alternatives, respectively. The assembled test vehicles were cut into two panels - one containing a resistor section for isothermal aging and the other containing a BGA and another resistor section for thermal shock. The assemblies were subjected to isothermal aging and thermal shock tests as per Interconnecting and Packaging Electronic Circuits/Joint Electronic Device Engineering Council (IPC/JEDEC) standards. The resistors were sheared in the as-soldered condition, and at various isothermal aging intervals and thermal shock cycles. In order to simulate an intermetallic failure in isothermal aging, a reduced shear height (20 mum) was used for the shear test. The performance of the resistor solder joints were quantified in terms of the shear force. The performance of the ball grid array (BGA) solder joint during thermal shock testing was quantified in terms of the number of cycles to failure. Experimental results from shear analysis of resistor solder joints show that Pb-free alloy assemblies' performance is superior to those assembled using Sn-Pb alloy. Also, the ductile nature of the Sn-Ag-Cu (SAC) alloy provides the joints a better fatigue life. With the area array components, Pb-free assembly joints outlived the traditional Sn-Pb joints when subjected to thermal shock loading. Among the mixed assemblies, backward-compatible assemblies (Pb-free bumps and Sn-Pb solder alloy) showed superior performance. The microstructural analysis of the solder joints indicate a uniform distribution of lead in the solder joint matrix.

Component Mode Synthesis Methods for 3-D Heterogeneous Core Calculations Applied to the Mixed-Dual Finite Element Solver MINOS

This paper describes a new technique for determining the pin power in heterogeneous three-dimensional calculations. It is based on a domain decomposition with overlapping subdomains and a component mode synthesis (CMS) technique for the global flux determination. Local basis functions are used to span a discrete space that allows fundamental global mode approximation through a Galerkin technique. Two approaches are given to obtain these local basis functions. In the first one (the CMS method), the first few spatial eigenfunctions are computed on each subdomain, using periodic boundary conditions. In the second one (factorized CMS method), only the fundamental mode is computed, and we use a factorization principle for the flux in order to replace the higher-order eigenmodes. These different local spatial functions are extended to the global domain by defining them as zero outside the subdomain. These methods are well fitted for heterogeneous core calculations because the spatial interface modes are taken into account in the domain decomposition. Although these methods could be applied to higher-order angular approximations—particularly easily to an SPN approximation—the numerical results we provide are obtained using a diffusion model. We show the methods’ accuracy for reactor cores loaded with uranium dioxide and mixed oxide assemblies, for which standard reconstruction techniques are known to perform poorly. Furthermore, we show that our methods are highly and easily parallelizable.

A study of the non-linear behaviour of adhesively-bonded composite assemblies

The objective of this study is to define a reliable tool for dimensioning of adhesively bonded assemblies, particularly for marine and underwater applications. This paper presents experimental and numerical results, which describe the non-linear behaviour of an adhesive in a bonded assembly for various loadings. A modified Arcan fixture, well-suited for the study of the behaviour of bonded metal–metal assemblies, was developed in order to focus on the analysis of the behaviour of the adhesive in thin films. The edge effects are minimised by using an appropriate design of the substrates so that experimental results give reliable data. To analyze the kinematics of the deformation of the adhesive joint non-contact extensometry techniques were employed. Thus, various characteristics of the non-linear behaviour of the adhesive were observed. The results obtained for mixed assemblies (steel, aluminium, composite substrates) show similar behaviour of the adhesive using the proposed procedure. Furthermore, quality controls by DSC, and studies of curing by DMA have been performed to verify the bonding procedure.

Reliability Investigation of Mixed BGA Assemblies

The effect of different reflow profiles on the reliability of lead-free (LF) Sn-3.0 Ag-0.5 Cu (wt.%) (SAC 305) ball grid array (BGA) devices assembled with a SnPb eutectic paste was investigated. The memory modules in a back-to-back configuration were reflowed on standard graphic cards finished with immersion silver (IAg) or hot air solder leveling (HASL) coatings. The reflow peak temperatures ranged from 209 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C to 227 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C, while the time above liquidus (TAL) varied from 45 to 80 s. Depending on the reflow conditions, the solder interconnects displayed varied degrees of SnPb and LF solders intermixing. It was established that in order to receive a homogeneous solder alloy, the reflow peak temperature had to be in the 218 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C–222 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C range. The reliability of solder interconnects of memory modules was assessed by subjecting the cards to 1500 cycles of accelerated thermal-cycling with a profile from 0 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C to 100 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C. It was found that the control SnPb/SnPb assemblies displayed superior reliability to that of the mixed assemblies. Regardless of the degree of homogeneity of the BGA balls, the predominant failure mode of the mixed solder joints was interfacial cracking through a Pb-rich phase near the intermetallic layer. In contrast, only partial cracks propagating diagonally through the bulk solder were present on the control boards. It was concluded that a combination of state of stress and segregation of the Pb-rich phase at the interface was responsible for the shortened thermal–mechanical fatigue life of the mixed solder interconnects.

Hydrotropic Enhancement of Rate of Ninhydrin‐α‐Amino Acid Reaction: A Kinetic Study

The kinetics of ninhydrin‐α‐amino acid (alanine, phenylalanine, and valine) reaction have been studied in the absence and in the presence of a common hydrotrope, sodiumbenzoate. A strong enhancement in the rate of reaction has been observed in the presence of the hydrotrope above its minimal hydrotrope concentration (MHC). The order of reaction in ninhydrin was always found to be unity while that in amino acid decreases from unity to zero at higher [Aminoacid]. A mechanism consistent with kinetic data and involving the formation of a mixed aggregation assemblies between amino acid and hydrotrope has been proposed.

Experimental and Numerical Investigation of the Reliability of Double-Sided Area Array Assemblies

One of the primary advantages of surface mount technology (SMT) over through-hole technology is that SMT allows the assembly of components on both sides of the printed circuit board (PCB). Currently, area array components such as ball grid array (BGA) and chip-scale package (CSP) assemblies are being used in double-sided configurations for network and memory device applications as they reduce the routing space and improve electrical performance (Shiah, A. C., and Zhou, X., 2002, “A Low Cost Reliability Assessment for Double-Sided Mirror-Imaged Flip Chip BGA Assemblies,” Proceedings of the Seventh Annual Pan Pacific Microelectronics Symposium, Maui, Hawaii, pp. 7–15, and Xie, D., and Yi, S., 2001, “Reliability Design and Experimental work for Mirror Image CSP Assembly”, Proceedings of the International Symposium on Microelectronics, Baltimore, October, pp. 417–422). These assemblies typically use a “mirror image” configuration wherein the components are placed on either side of the PCB directly over each other; however, other configurations are possible. Double-sided assemblies pose challenges for thermal dissipation, inspection, rework, and thermal cycling reliability. The scope of this paper is the study of the reliability of double-sided assemblies both experimentally and through numerical simulation. The assemblies studied include single-sided, mirror-imaged, 50% offset CSP assemblies, CSPs with capacitors on the backside, single-sided, mirror-imaged plastic ball grid arrays (PBGAs), quad flat pack (QFP)/BGA mixed assemblies. The effect of assembly stiffness on thermal cycling reliability was investigated. To assess the assembly flexural stiffness and its effect on the thermal cycling reliability, a three-point bending measurement was performed. Accelerated thermal cycling cycles to failure were documented for all assemblies and the data were used to calculate the characteristic life. In general, a 2X to 3X decrease in reliability was observed for mirror-image assemblies when compared to single-sided assemblies for both BGAs and CSPs on 62mil test boards. The reliability of mirror-image assemblies when one component was an area array device and the other was a QFP was comparable to the reliability of the single-sided area array assemblies alone, that is, the QFP had almost no influence on the double-sided reliability when used with an area array component. Moiré interferometry was used to study the displacement distribution in the solder joints at specific locations in the packages. Data from the reliability and moiré measurements were correlated with predictions generated from three-dimensional finite element models of the assemblies. The models incorporated nonlinear and time-temperature dependent solder material properties and they were used to estimate the fatigue life of the solder joints and to obtain an estimate of the overall package reliability using Darveaux’s crack propagation method.

Sequential Energy and Electron Transfer in Aggregates of Tetrakis[oligo(p-phenylene vinylene)] Porphyrins and C60 in Water

Chiral aggregation of oligo(p-phenylene vinylene)-functionalized Zn and free-base porphyrins is observed in water. The formation of mixed assemblies containing both porphyrins results in sequential energy transfer from OPV via zinc porphyrin to free-base porphyrin. Furthermore, the incorporation of C60 as electron acceptor yields a charge separated state by ultimate electron transfer.

Comparison of three different kinematic sensor assemblies for locomotion study

The decrease in the costs of electronic components and devices, conjugated to the advancement of the miniaturization technologies, has promoted a large profusion of the use of motion sensors for human movement analysis in clinics. The errors in the design are numerous, from circuital errors to positioning and orientation errors; a preliminary approach to the problem by means of simulations is necessary. We developed an environment for the simulation of mixed kinematic sensor assemblies with accelerometers and rate gyroscopes; it was tested by means of three different assemblies in the simulation of the trajectory reconstruction. The first assembly was represented by a 6-accelerometer assembly, the second by a 9-accelerometer assembly and the third was based on three rate gyroscopes and three accelerometers. The circuital error, given as an input to the environment, was determined during a bench test, the positioning error was set to pe = 5 × 10−4 m and the orientation error to αe = 6 × 10−2 deg. Results showed the agreement between estimated and experimental data from the bench test. Simulation results also showed that the errors in trajectory reconstruction in the sagittal plane were lower than 3–4% during 4 s of simulation.

Thermodynamically stable vesicle formation from glycolipid biosurfactant sponge phase

Thermodynamically stable vesicle (L α1) formation from glycolipid biosurfactant sponge phase (L 3) and its mechanism were investigated using a “natural” biocompatible mannosyl-erythritol lipid-A (MEL-A)/ l-α-dilauroylphosphatidylcholine (DLPC) mixture by varying the composition. The trapping efficiency for calcein and turbidity measurements clearly indicated the existence of three regions: while the trapping efficiencies of the mixed MEL-A/DLPC assemblies at the compositions with X DLPC ≤ 0.1 or X DLPC ≥ 0.8 were almost zero, the mixed assemblies at the compositions with 0.1 < X DLPC < 0.8 had some trapping efficiency, and in particular the composition with X DLPC = 0.3 exhibited the maximum trapping efficiency. Confocal laser scanning microscopy (CLSM) and freeze–fracture electron microscopy (FFEM) determined that the assemblies in the compositions with X DLPC ≤ 0.1 were droplets with a sponge phase (L 3) with diameter from 2 to 20 μm and those of X DLPC ≥ 0.8 were multilamellar vesicles (L α) with diameter from 2 to 10 μm. Meanwhile, dynamic light scattering (DLS) measurement revealed that the average size of the vesicles at the composition of X DLPC = 0.3 was 633.2 nm, which is remarkably small compared to other compositions. Moreover, the mixed vesicle solution at the composition of X DLPC = 0.3 was slightly bluish and turbid and kept its dispersion stability at 25 °C for more than 3 months, indicating the formation of a thermodynamically stable vesicle (L α1). These results exhibited the formation of a thermodynamically stable vesicle (L α1) with a high dispersibility from the MEL-A/DLPC mixture. The asymmetric distribution of MEL-A and DLPC in the two vesicle monolayers caused by the difference in geometrical structures is very likely to have changed their self-assembled structure from a sponge phase (L 3) to a thermodynamically stable vesicle (L α1).

Control of two-dimensional aggregates of a long-chain merocyanine by change of molecular environments in monolayer assemblies

An amphiphilic unsymmetrical merocyanine forms J- and H-aggregates by changing molecular environments in the binary and the ternary mixed monolayer assemblies, which have been characterized by visible absorption spectra films having red-shifted and blue-shifted bands in comparison with the solution spectrum, respectively. From the surface pressure–area isotherms of the mixed monolayers, the film structures were studied at the air/water interface. The in-plane X-ray diffraction and the atomic force microscopy measurements of their LB films were done to observe the fine lattice structure. The aggregate structures were well corresponding to the dye arrangements speculated by calculation with an extended dipole model for the spectral shifts.