Microstructure and mechanical properties of Pb-free solder alloys for low-cost electronic assembly: A review

Lead-free solders, including Sn-58Bi, Sn-52In, and Sn-3.5Ag, are potential replacements for Sn-37Pb solder in low-cost electronic assembly. This paper reviews the literature on the microstructure and mechanical properties of these alloys. Because of the processing and testing conditions, many of the data are not predictive for electronic assembly applications. However, eutectic Sn-Bi seems to have properties approaching those of eutectic Sn-Pb under most conditions, while eutectic Sn-In seems far inferior in most respects. Eutectic Sn-Ag has many promising characteristics, but its relatively high melting temperature may preclude its use for this type of application.     

Fast full‐color reflective display via photoluminescent enhancement

Reflective displays are advantageous in applications requiring low power or daylight readability. However, there are no low‐cost reflective technologies capable of displaying bright colors. By employing photoluminescence to more efficiently use ambient light, we created a prototype display that provides bright, full color in a simple, low‐cost architecture. This prototype includes a novel electrokinetic shutter, a layer that incorporates patterned luminescent red, green, and blue sub‐pixel elements, and a novel optical out‐coupling scheme. The luminescent elements convert otherwise‐wasted portions of the incident spectrum to light in the desired color band, resulting in improved color saturation and lightness. This prototype provides a color gamut that is superior to competing reflective display technologies that utilize color filters in single‐layer side‐by‐side sub‐pixel architectures. The current prototype is capable of switching in <0.5 s; future displays based on an alternative electro‐optic shutter technology should achieve video rate operation. A transflective version of this technology has also been prototyped. The transflective version utilizes its backlight with a power efficiency that is at least three times that of a conventional liquid crystal display. These photoluminescence‐based technologies enable a host of applications ranging from low‐power mobile products and retail pricing signage to daylight readable signage for outdoor advertising segments.     

High Definition Digital Fabrication of Active Organic Devices by Molecular Jet Printing

We introduce a high resolution molecular jet (MoJet) printing technique for vacuum deposition of evaporated thin films and apply it to fabrication of 30 μm pixelated (800 ppi) molecular organic light emitting devices (OLEDs) based on aluminum tris(8‐hydroxyquinoline) (Alq₃) and fabrication of narrow channel (15 μm) organic field effect transistors (OFETs) with pentacene channel and silver contacts. Patterned printing of both organic and metal films is demonstrated, with the operating properties of MoJet‐printed OLEDs and OFETs shown to be comparable to the performance of devices fabricated by conventional evaporative deposition through a metal stencil. We show that the MoJet printing technique is reconfigurable for digital fabrication of arbitrary patterns with multiple material sets and high print accuracy (of better than 5 μm), and scalable to fabrication on large area substrates. Analogous to the concept of “drop‐on‐demand” in Inkjet printing technology, MoJet printing is a “flux‐on‐demand” process and we show it capable of fabricating multi‐layer stacked film structures, as needed for engineered organic devices.     

Colour and tolerance of preferred skin colours on digital photographic images

Skin‐tone has been an active research subject in photographic colour reproduction. There is a consistent conclusion that preferred skin colours are different from actual skin colours. However, preferred skin colours found from different studies are somewhat different. To have a solid understanding of skin colour preference of digital photographic images, psychophysical experiments were conducted to determine a preferred skin colour region and to study inter‐observer variation and tolerance of preferred skin colours. In the first experiment, a preferred skin colour region is searched on the entire skin colour region. A set of nine predetermined colour centers uniformly sampled within the skin colour ellipse in CIELAB a*b* diagram is used to morph skin colours of test images. Preferred skin colour centers are found through the experiment. In a second experiment, a twice denser sampling of nine skin colour centers around the preferred skin colour center determined in the first experiment are generated to repeat the experiment using a different set of test images and judged by a different panel of observers. The results from both experiments are compared and final preferred skin colour centers are obtained. Variations and hue and chroma tolerances of the observer skin colour preference are also analysed. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013     

Epoxidized perfluoropolyethers: A route to hydrophobic,negative‐tone photoresists

The synthesis, formulation, and wafer level processing conditions of a heavily fluorinated hydrophobic photoresist was demonstrated. The synthesis is based on terminal epoxy modification of commercially available perfluoropolyethers. Structural characterization shows that terminal epoxide can open during the synthetic process, but in a simple formulation has a negligible effect on photoresolution of the photoresist. Formulation into a traditional photoresist requires careful selection of appropriate cosolvents to ensure solubility of the hydrophobic epoxy and hydrophilic photoacid generator while attaining adequate coating quality. Formulation processing conditions are presented and the chemical resistance of the resist through aggressive processing steps is demonstrated. Wafer level patterning using traditional photolithographic tools illustrates the applicability of the formulation and process conditions for traditional resist or microfluidic applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Linewidth control for 0.25 micron gate patterning

Linewidth control of small lines over non-planarized topography is particularly challenging due to resist thin film interference effects and reflective notching. This paper compares the linewidth control performance of several deep-UV resist processes, using dyed resist and both top and bottom anti-reflection coatings. Only the bottom anti-reflective coating (BARC) provides adequate linewidth control for development work on 0.25 micron gate patterning. The BARC and resist coating behavior over isolation topography is characterized using atomic force microscopy and correlated to residual linewidth variation. The performance of a zero bias etch process for BARC removal is also presented.     

A reproducible ohmic contact to n-type GaAs0.6P0.4

A study is reported on several alternate metal systems based upon AuGeNiCr, which provide reproducibly $\text{～10}{}^{\mathrm{?4}}\text{Ω-}\text{cm}{}^2$ specific contact resistance to n-type GaAs_0.6P_0.4, employing the conventional open-tube sintering furnace. A simple metallurgical model is presented to explain the success of this technique. It is found that a thin chromium-oxide film is formed during the heat treatment, which is thought to prevent metal pads from balling-up, and volatile components of the semiconductor from evaporating. In this way, the metal-semiconductor interface re-growth process is optimized to consistently provide low resistance ohmic contacts.     

A Decision Process Implementation for Microwave Near-Field Characterization of Concrete Constituent Makeup

Determination of concrete compressive strength is one of the most important factors in the construction industry. Concrete is a mixture of cement, water, sand (fine aggregate) and rock (coarse aggregate) of various sizes. Water and cement chemically bind to form the cement paste phase of concrete, which primarily influences the compressive strength. The aggregate content mainly acts as a filler but also influences the compressive strength of concrete. Currently, there is no single method for nondestructive determination of compressive strength of concrete. As a result, the only reliable method of compressive strength measurement is to core a specimen from an existing structure and perform a compressive failure test. In recent years, studies on the reflection properties of concrete with varying material content have been performed using microwave nondestructive testing techniques. These techniques, employing open-ended rectangular waveguide probes, have shown tremendous potential for determining concrete constituent makeup. The results have demonstrated that microwave reflection property measurements of concrete as a function of varying constituent makeup, possess statistical properties that provide for a unique fingerprint. In this paper a simple decision process is proposed, based on the maximum likelihood ratio, which uses the a priori statistical distribution of microwave reflection measurements for material content determination of concrete specimens. The results show that by simply performing two sets of microwave reflection property measurements at 3 and 10 GHz, the constituent makeup of an unknown concrete specimen can be very closely determined. Subsequently, the compressive strength of the specimen could be easily determined from a simple lookup table relating constituent makeup and compressive strength, which are readily available in the industry.     

A Web-Based Secure System for the Distributed Printing of Documents and Images

We propose and consider a secure printing system for the distributed printing of documents and images over the World Wide Web. The main feature of the system is that it allows previewing and printing of selected documents and images, where only a certain number of hardcopies can be generated based on an agreed payment. The security of the system resides on an aggregate of communication protocols, smartcard technologies, and cryptographic algorithms. The system prevents eavesdropping in that people who intercept the communication cannot generate copies of the document.