Current Problems and Possible Solutions in High-Temperature Lead-Free Soldering

The substitution of lead in the electronics industry is one of the key issues in the current drive towards ecological manufacturing. Legislation has already banned the use of lead in solders for mainstream applications (T _M ≈ 220 °C), but the use of lead in the solders for high-temperature applications (>85% lead, T _M ≈ 250-350 °C) is still exempt in RoHS2. The search for proper substitutes has been ongoing among solder manufacturers only for a decade without finding a viable low cost alternative and is the subject of intensive research. This article tries to map the current situation in the field of high-temperature lead-free soldering, presenting a short review of current legislation, requirements for substitute alloys, and finally it describes some existing solutions both in the field of promising new materials and new technologies. Currently, there is no drop-in replacement for lead-containing solders and therefore both the new materials and the new technologies may be viable solutions for production of reliable lead-free joints for high-temperature applications.     

Target adjustment and self-other agreement: Utilizing trait observability to disentangle judgeability and self-knowledge.

Are well-adjusted individuals good targets or accurate self-judges? Across two round-robin studies, the current research first demonstrates that well-adjusted individuals' personalities are viewed with greater distinctive self-other agreement by new acquaintances. Is this enhanced self-other agreement a function of greater judgeability, improving others' ability to form an accurate impression? Or is it a function of greater self-knowledge, having a more accurate impression about oneself? By examining the relationship between psychological adjustment and self-other agreement as a function of trait observability, it becomes clear that psychological adjustment fosters self-other agreement through judgeability more so than through self-knowledge. Specifically, well-adjusted individuals provide new acquaintances with greater information regarding their less observable traits, enhancing others' knowledge and thus distinctive self-other agreement. This effect was replicated with close informant-other agreement, indicating that the well-adjusted individual's tendency to make his or her less visible traits more accessible to others allows those who just met the target to agree better with people who know the target well. In sum, although well-adjusted individuals are in part good self-judges, it is their greater judgeability that seems most critical in enhancing self-other agreement in first impressions. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Needle-disk electrospinning inspired by natural point discharge

Point discharge is a natural phenomenon which principle and application are both under active investigation. In this work, a needle-disk electrode spinneret was designed through the combination of the point discharge concept and the merits of typical needleless electrospinning (disk as spinneret). The desired outcome for point electrode system is to produce a controllable process of jet formation, with respect to the control of jet site and amount of jets under a lower applied voltage value. Two comparisons were used: (i) in comparison to the typical needleless electrospinning method (disk electrospinning), the needle-disk electrospinning produce finer and more uniform nanofibers. Further numerical simulation results confirmed that the needle-disk electrode induced electric field intensity which is 5.33 times higher than that of disk electrode under the same parameters; (ii) both the numerical simulation and experimental results showed that needle-disk electrospinning can produce competitive quality of nanofibers accompanied by enhanced throughput, compared with the traditional single-needle electrospinning method. Finally, we demonstrate that needle-disk electrospinning produces nanofiber with super-high throughput of 13.5 g/h, which is 183 times higher than traditional electrospinning under similar spinning conditions.     

Simulating Particle Size Distributions over California and Impact on Lung Deposition Fraction

Reliable simulations of particle mass size distributions by regional photochemical air quality models are needed in regulatory applications because the U.S. EPA's National Ambient Air Quality Standards specify limits on the mass concentration of particles in a specific size range (i.e., aerodynamic diameter <2.5 μm). Considering the associations between adverse health effects and exposure to ultrafine particles, air quality models may need to accurately simulate particle number size distributions in addition to mass size distributions in future applications. In this study, predictions of particle number and mass size distributions by the Community Multiscale Air Quality model with the standard and an updated emission size distribution are evaluated using wintertime observations in California. Differences in modeled lung deposition fraction for simulated and observed particle number size distributions are also evaluated. Simulated mass size distributions are generally broader and shifted to larger diameters than observations, and observed differences in inorganic and carbon (elemental and organic) distributions are not captured by the model. These model limitations can be reasonably accounted for in regulatory modeling applications. Simulated number size distributions are considerably less accurate than mass size distributions and are difficult to represent in air quality models due to large sub-grid-scale concentration gradients. However, modeled number size distributions are responsive to updates of the emission size distribution, and reasonable simulation of background number size distributions might be possible with an improved treatment of emission size distributions. Modeled lung deposition fractions for simulated number size distributions peak in the same lung region as those for number size distributions observed in the background. However, differences in modeled and observed total number concentrations generally suggest large differences in the total number of deposited particles. Future model development on simulating particle mass size distributions should focus on improving predictions of the mass fraction of particles <2.5 μm. Model development for particle number size distributions should focus on reducing differences in modeled lung deposition for modeled and observed distributions.     

An Investigation of the Failure Mechanisms of a Polymer Matrix Composite Crew Oar

Journal of Failure Analysis and Prevention - Rowing, or crew, is a constantly evolving sport with an impressive history of equipment advancements, including the use of advanced polymer matrix...     

The sources of heat generation in vibrothermography

Vibrothermography, or sonic IR, is a nondestructive evaluation technique used to find surface and near surface defects—such as cracks and delaminations—through observations of vibration-induced heat generation. This method has significant interest as an industrial inspection method, however, a lack of understanding of the fundamental physics governing the heat generation process has limited its application despite extensive theoretical, numerical simulation, and experimental work. Significant theoretical and numerical simulation work has been performed, but has yet to be rigorously verified experimentally. This paper presents experimental verification of the sources of heat generation in vibrothermography; specifically friction, plasticity, and viscoelasticity. Specific experimental evidence is presented that verifies each of these heat-generating mechanisms.     

Additive manufacturing of zirconia parts with organic sacrificial supports

Ceramic On-Demand Extrusion (CODE) process has been recently proposed for additive manufacturing of strong ceramic components via extrusion. This paper focuses on fabricating 3 mol% yttria-stabilized zirconia (3YSZ) components using CODE process, and enabling CODE to produce parts with support structures. A colloidal suspension of 3YSZ was developed and deposited through the main nozzle, and an organic feedstock was developed and deposited by means of another nozzle to fabricate supports. After printing and drying of raw parts, supports were removed by increasing the temperature and parts were then sintered to near theoretical (~99%) density. The maximum overhang angle that could be built with no support was also found out to be approximately 60 degrees. Three organic support materials, that is, polycaprolactone (PCL), silicone, and petrolatum were prepared and tested. PCL and petrolatum were identified as feasible support materials. Specimens were fabricated to validate the efficiency of the support materials and to evaluate CODE's capability for building parts with complex geometry. The microstructures of these parts were also analyzed via scanning electron microscopy.     

UV initiated formation of polymer monoliths in glass and polymer microreactors

Polymer monoliths with good flow-through properties were prepared by UV initiated polymerisation to form a support for heterogeneous palladium catalysis in glass and polymer microchips. Preparation of homogeneous polymer monoliths required investigation of different light source/photoinitiator combinations and manipulation of the polymerisation mixture to accommodate different channel dimensions. A deep UV (DUV) flood exposure lamp, UV tubes with respective outputs at 255 and 365 nm and a UV LED array with output at 365 nm were used to initiate the polymerisation. The spectra of light source and initiator were matched; 2,2-dimethoxy-2-phenylacetophenone (DMPAP) was selected for polymerisation in the DUV and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) was used for polymerisation in the near UV (NUV). This is the first report of the use of a BAPO-type photoinitiator for the formation of organic polymer monoliths. Only the DUV lamp and 365 nm UV LED array resulted in the formation of homogenous and continuous monoliths which were subsequently used to create continuous-flow microreactors in fused silica capillaries, borosilicate chips and in cyclic olefin copolymer (COC) capillaries and chips. All microreactors gave high to quantitative yields for the Suzuki-Miyaura's coupling of iodobenzene with 4-tolyl boronic acid. In addition to demonstrating the first polymer chip for heterogeneous Suzuki-Miyaura's catalysis, the UV LED array in combination with BAPO was found to be a suitable budget alternative to a DUV exposure source for monolith formation in devices with internal diameter of up to 2 mm.