Development of Stretch Solder Interconnections for Wafer Level Packaging

A wafer level packaging technique has been developed with an inherent advantage of good solder joint co-planarity suitable for wafer level testing. A suitable weak metallization scheme has also been established for the detachment process. During the fabrication process, the compliancy of the solder joint is enhanced through stretching to achieve a small shape factor. Thermal cycling reliability of these hourglass-shaped, stretch solder interconnections has been found to be considerably better than that of the conventional spherical-shaped solder bumps.     

Local pixel statistics based impulse detection and hybrid color filtering for restoration of digital color images

This paper presents a two stage filtering system to remove random valued impulse noise from color images based on local statistics of the filtering window under consideration. In the first stage, to detect the noisy pixel, the locally adaptive threshold is derived from the pixels of the filtering window. In the second stage, the restoration of the noisy pixel is done on the basis of brightness and chromaticity information obtained from the neighbouring pixels in the filtering window. Simulation results show that the proposed scheme yields much superior performance in comparison with other color image filtering methods.     

A bandwidth-efficient method for cancellation of ICI in OFDM systems

Orthogonal frequency division multiplexing (OFDM) is a very important modulation technique in wideband wireless communication and multimedia communication systems. While, it can effectively deal with multipath delay spread produced by frequency fading channels, its main drawback is the effect of frequency offset (FO) produced by the receiver local oscillator or by motion-induced Doppler. The FO breaks the orthogonality among the subcarriers and hence causes intercarrier interference (ICI). In this paper, ICI caused by frequency drift is eliminated by equalizing the complex weighting coefficients of interference. In most of the commonly used ICI cancellation schemes, bandwidth efficiency suffers because of the requirement of redundancy in the transmission. In the proposed scheme, repetition of data symbols or transmission of training sequence is not required. Thus, the bandwidth efficiency of normal OFDM system is maintained. The improved performance of the present scheme is confirmed through extensive simulations.     

Moisture absorption and diffusion characterisation of packaging materials––advanced treatment

Unlike thermo-mechanical properties, moisture properties of packaging materials are rarely reported, even though moisture has been known to be at least as damaging as temperature to plastic packaging. This is in part due to the lack of characterisation knowledge for such properties.This paper tries to address this issue through a comprehensive presentation of the characterisation techniques for moisture sorption and diffusion properties. Special focuses are given to advanced treatments on unique characteristics of polymeric packaging materials. The effect of aspect ratio of the test specimen on characterisation accuracy has been analysed and correction factor has been formulated. Two techniques for characterising anisotropic diffusivity are presented and illustrated with actual experimental data on organic laminates. The techniques and challenges of characterising moisture diffusivity at high temperature are presented. A new insight into the causes and physics of non-Fickian adsorption in polymeric packaging materials is presented along with a technique to alleviate the associated characterisation challenge.     

Intelligent selection of threshold in covariance-based spectrum sensing for cognitive radio networks

Wireless Networks - The radio spectrum sensing has been an important issue of research in cognitive radio networks over the last decade and the appropriate selection of threshold plays a crucial...     

High-Speed Cyclic Bend Tests and Board-Level Drop Tests for Evaluating the Robustness of Solder Joints in Printed Circuit Board Assemblies

This paper presents a comprehensive study of the resistance of solder joints to failure when subjected to strain rates that simulate the conditions of drop impact experienced by a portable electronic product. Two test methods are used in this study: the board-level drop-shock test (BLDST) and the board-level high-speed cyclic bend test (HSCBT). The performance of (i) 12 material combinations consisting of six solder alloys and two pad finishes, and (ii) 11 manufacturing variations covering three vendors, two finishes, three immersion gold thicknesses, and three thermal aging conditions were investigated using these two test methods. Correlations between the two test methods were performed. Quantitative correlation and sensitivity coefficients for the failure modes and the measured characteristic parameters—number of drops to failure for BLDST and number of cycles to failure for HSCBT—were evaluated. Finally, the potential of HSCBT as a test method for material selection and for bridging board-level and product-level tests was demonstrated through generation of board strain versus number of cycles to failure (S–N) curves of solder joints for six material systems, four bending frequencies, and two test temperatures.     

Comprehensive treatment of moisture induced failure-recent advances

This paper describes a comprehensive treatment of moisture induced failure in integrated circuit (IC) packaging with emphasis on recent advances. This includes advanced technique for modeling moisture diffusion under dynamic boundary conditions such as experienced by packages during solder reflow, autoclave, and temperature-humidity cycling; advanced characterization technique for moisture sorption and diffusion properties of packaging materials including effect of edge diffusion on transverse diffusivity, anisotropic diffusivity in organic laminates, impact of non-Fickian sorption; advanced techniques for modeling vapor pressure during solder reflow; advanced techniques for modeling dynamic delamination propagation during solder reflow; interfacial fracture strength as a function of temperature and moisture; as well as plastic analysis of popcorn cracking.     

Steady state performance evaluation of variable geometry twin-entry turbine

This paper presents the results from an experimental investigation conducted on different turbine designs for an automotive turbocharger. The design progression was based on a commercial nozzleless unit that was modified into a variable geometry single and twin-entry turbine. The main geometrical parameters were kept constant for all the configurations and the turbine was tested under steady flow conditions.A significant depreciation in efficiency was measured between the single and twin-entry configuration due to the mixing effects. The nozzleless unit provides the best compromise in terms of performance at different speeds.The twin-entry turbine was also tested under partial and unequal admissions. Based on the test results a method to determine the swallowing capacity under partial admission given the full admission map is presented. The test results also showed that the turbine swallowing capacity under unequal admission is linked to the full admission case.     

Analysis of NOMA based UAV assisted short-packet communication system and blocklength minimization for IoT applications

Wireless Networks - Recently, academia and industry have shown keen interest in achieving ultra-reliable and low latency communication (URLLC) through short-packet communication to meet the strict...     

Refractive indices variation with temperature and humidity of optical adhesive

Refractive index and birefringence of optical adhesives is studied under different environmental exposures, such as temperature, humidity, and annealing. Refractive index of the adhesive decreases at a higher rate for the temperature treatment compared to the humidity exposure. A sudden decrease in the rate of refractive index (thermo-optic coefficient, dn/dT), from −2×10⁻⁴°C⁻¹ to −4×10⁻⁴°C⁻¹ was observed near the glass transition temperature. The adhesive’s refractive index (n) was studied during the moisture desorption cycle. Refractive index of the adhesive was found to increase at a constant rate with moisture. The change in refractive index of the adhesive upon moisture absorption was found to be irreversible. Birefringence (T_E — T_M) decreases with higher annealing temperature treatment of the adhesive, because the rate of increase in refractive indices for T_E and T_M modes is not similar. The refractive index in T_M mode increases at a higher rate compared to that in the T_E mode. This suggests that the material has become more isotropic due to annealing. The environmental changes in optical properties of the adhesive are discussed in light of Lorenz-Lorentz equations.