Stencil printing behavior of lead-free Sn-3Ag-0.5Cu solder paste for wafer level bumping for Sub-100 μm size solder bumps

Stencil printing for flip chip packaging using fine particle solder pastes is a low cost assembly solution with high throughput for fine pitch solder joint interconnects. The manufacturing challenges associated with both solder paste printing increases as electronic device size decreases due to trend of miniaturization in electronic components. Among multiple parameters, the two most important stencil printing parameters are squeegee pressure and printing speed. In this paper, the printing behavior of Pb free Sn-3Ag-0.5Cu solder paste with a particle size distribution of 2–12 μm for wafer level bumping using a stencil printing method (stencil opening dimension ?30 μm) was evaluated by varying the printing speed and squeegee pressure to fabricate solder bumps with a sub 100 μm size. The optimal squeegee pressure and print speed for the defect free printing behavior and fairly uniform size distribution of reflowed paste were found to be 7 kgf and 20 mm/s, respectively. The average size of the reflowed printed paste decreased with the increasing squeegee pressure.     

Signal processing for real-time identification of similar metals by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS) is regarded as a promising technique for realtime sorting of scrap metals due to its capability of fast multi-elemental and in-air analysis. This work reports a method for signal processing which ensures high accuracy and high speed during similar metal sorting by LIBS. Similar metals such as aluminum alloys or stainless steel are characterized by nearly the same constituent elements with slight variations in elemental concentration depending on metal type. In the proposed method, the original data matrix is substantially reduced for fast processing by selecting new input variables(spectral lines) using the information for the constituent elements of similar metals. Specifically, principal component analysis(PCA) of full-spectra LIBS data was performed and then, based on the loading plots, the input variables of greater significance were selected in the order of higher weights for each constituent element. The results for the classification test with aluminum alloy, copper alloy,stainless steel and cast steel showed that the classification accuracy of the proposed method was nearly the same as that of full-spectra PCA, but the computation time was reduced by a factor of 20 or more. The results demonstrated that incorporating the information for constituent elements can significantly accelerate classification speed without loss of accuracy.     

Event justice perceptions and employees' reactions: Perceptions of social entity justice as a moderator.

Building on 2 paradigms in organizational justice research and on fairness heuristic theory, the author argues that employees' perceptions about the fairness of social entities (their supervisor and their organization) moderate the relationship between their perceptions about the fairness of specific events and their reactions. A survey of 265 supervisor-employee pairs in 4 companies was conducted to test this argument. Hierarchical linear modeling analyses showed that when employees perceived their organization to be generally fair, this perception moderated the relationship between the perceived justice of a particular event and their reactions to the organization (organizational commitment and organization-directed citizenship behavior). In addition, employees' perceptions of the fairness of their supervisor were found to moderate the relationship between the perceived justice of a particular event and their supervisor-directed responses (trust in managers and supervisor-directed citizenship behavior) and their organization-directed responses. The results suggest that employee attitudes and behavior can be better understood when both event justice perceptions and social entity justice perceptions are considered together. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enzymatic Polymerization on DNA Modified Gold Nanowire for Label-Free Detection of Pathogen DNA

This paper presents a label-free biosensor for the detection of single-stranded pathogen DNA through the target-enhanced gelation between gold nanowires (AuNW) and the primer DNAs branched on AuNW. The target DNA enables circularization of the linear DNA template, and the primer DNA is elongated continuously via rolling circle amplification. As a result, in the presence of the target DNA, a macroscopic hydrogel was fabricated by the entanglement of the elongated DNA with AuNWs as a scaffold fiber for effective gelation. In contrast, very small separate particles were generated in the absence of the target DNA. This label-free biosensor might be a promising tool for the detection of pathogen DNAs without any devices for further analysis. Moreover, the biosensor based on the weaving of AuNW and DNAs suggests a novel direction for the applications of AuNWs in biological engineering.     

Enzyme‐Driven Hasselback‐Like DNA‐Based Inorganic Superstructures

DNA structures have gained much attention due to its ease of self‐assembly and precise controllability. Although DNA technology has been successfully applied to generate a variety of DNA structures, there are only few attempts to apply DNA technology to generate inorganic materials due to lack of controllability of interactions between DNA and inorganic materials. In addition, the synthesis of a predictable structure of hybrid materials still remains a significant challenge. To address the challenge, here a novel strategy for the synthesis of DNA‐based inorganic superstructures using DNA polymerase is reported. In particular, strategic feeding of metal ions for generating DNA‐inorganic hybrid superstructures during DNA polymerization is established. This approach can produce a variety of structures with varying metal ions and can easily add functionality to the product. The structural features are also easily studied by first‐principles calculations. With these advantages, DNA‐Mn particles show the potential as a cell tracking agent, a contrast agent for MRI, and an electrode material for supercapacitors. The enzyme‐driven synthesis in this study will provide a novel route for the generation of a range of organic–inorganic hybrid superstructures for biomedical and energy applications.     

Social networks, personal values, and creativity: Evidence for curvilinear and interaction effects.

Taking an interactional perspective on creativity, the authors examined the influence of social networks and conformity value on employees’ creativity. They theorized and found a curvilinear relationship between number of weak ties and creativity such that employees exhibited greater creativity when their number of weak ties was at intermediate levels rather than at lower or higher levels. In addition, employees’ conformity value moderated the curvilinear relationship between number of weak ties and creativity such that employees exhibited greater creativity at intermediate levels of number of weak ties when conformity was low than when it was high. A proper match between personal values and network ties is critical for understanding creativity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New process of electroplate Sn bumping on TSV without a PR mould for 3D-chip stacking

A new method of fabricating Sn bumps by electroplating without a PR (photoresist) mould on a Si die was investigated in terms of the bump growth and morphology for application to 3D-chip stacking. The omission of the PR mould was expected to result in a reduction of the process time and of the cost of electroplate bumping on the Si chip. For the electroplating of Sn bumps, a cathode consisting of a Si die with a Cuplugged TSV (through-silicon via) was used, with Sn or Pt adopted as an anode. The current densities and plating times were varied to assess the change in the Sn bump size and morphology. As a result, Sn bumps with rivet-head shapes were successfully fabricated via electroplating on Cu-plugged TSV without a PR mould. The height and width of the Sn bump were increased at a longer plating time and a larger current density. The Sn or Pt anode had a minimal effect on the electroplating results: The deposition rates and morphologies of the Sn bumps with different anodes were nearly identical in the range from 15 to 60 min at −30 mA/cm². The Sn deposit without a PR mould developed a facet with various directions less than 5 min of plating time. After 15 min, however, the selective growth of some facets became dominant, which enlarged the preferred facets and caused a decrease in the number of facets.     

pH control for dyeing polyamide in a reused acid dyebath

The pH control that can be achieved in a reused dyebath was investigated. The study involved a phosphate buffer system and four pH sliding systems, including ammonium sulphate and three hydrolysable organic esters. Instead of discharging the dyebath after each dyeing cycle, the residual dyebath was analysed using a UV-Vis spectrophotometer and reconstituted to the required concentration of dyes, auxiliaries and acid donors. The dyebath was reused for 10 cycles and colour reproducibility, levelness and fastness of the dyed samples were measured after each recycling. In comparison with ammonium sulphate and sodium dihydrogen phosphate, hydrolysable organic esters gave a stable and effective pH shifting in the dyebath reuse system. In addition, hydrolysable organic esters resulted in a very low amount of salt in residual dyebath. No deterioration in colour fastness of the dyed fabrics over 10 cycles of dyebath reuse was evident.