Effect of current stressing on the reliability of 63Sn37Pb solder joints

The effect of current stressing on the reliability of 63Sn37Pb solder joints with Cu pads was investigated at temperatures of −5 °C and 125 °C up to 600 h. The samples were stressed with 3 A current (6.0 × 10² A/cm² in the solder joint with diameter of 800 μm and 1.7 × 10⁴ A/cm² in the Cu trace with cross section area of 35 × 500 μm). The temperatures of the samples and interfacial reaction within the solder joints were examined. The microstructural change of the solder joints aged at 125 °C without current flow was also evaluated for comparison. It was confirmed that the current flow could cause the temperature of solder joints to rise rapidly and remarkably due to accumulation of massive Joule heat generated by the Cu trace. The solder joints stressed at 125 °C with 3 A current had an extensive growth of Cu₆Sn₅ and Cu₃Sn intermetallic compounds (IMC) at both top and bottom solder-to-pad interfaces. It was a direct result of accelerated aging rather than an electromigration or thermomigration effect in this experiment. The kinetic is believed to be bulk diffusion controlled solid-state reaction, irrespective of the electron flow direction. When stressed at −5 °C with 3 A current, no significant change in microstructure and composition of the solder joints had occurred due to a very low diffusivity of the atoms as most Joule heat was eliminated at low temperature. The IMC evolution of the solder joints aged at 125 °C exhibited a subparabolic growth behavior, which is presumed to be a combined mechanism of grain boundary diffusion and bulk diffusion. This is mainly ascribed to the retardant effect against the diffusion course by the sufficiently thick IMC layer that was initially formed during the reflow soldering.     

Development of an end-point detector for parylene deposition process

Parylene is an emerging material for MEMS. It is an organic material that is grown by using the chemical vapor deposition method at room temperature. The deposition thickness is commonly controlled by the amount of solid-phase dimer loaded in a sublimation chamber. In a conventional deposition machine, the end point of the process is designated by the moment the dimer is exhausted. However, this end-of-process criterion does not offer precise, repeatable control of film thickness. We present the results of the development of an in situ end-point detector for a Parylene chemical vapor deposition process. The detector is based on the thermal transfer principle and can be implemented on commercial parylene deposition systems with minimal system modification. Such a sensor enables a user to stop the deposition when a targeted thickness is reached. The end point detector is very simple to implement on existing parylene deposition systems. A series of such sensors with different target deposition thickness would allow extraction of the actual deposition rate within a deposition run.     

Evaluating reactivity to ecological momentary assessment during smoking cessation.

Ecological momentary assessment (EMA) consists of assessing phenomena in real time in the natural environment. EMA allows for more fine-grained analyses of addictive behavior and minimizes threats to internal validity, such as recall biases and errors. However, because of the intensive monitoring involved in EMA, measurement reactivity is a concern. To test whether EMA with palmtop personal computers induces reactivity, the authors compared smoking-related outcomes between smokers using EMA and those not using EMA during a quit attempt. The use of no-EMA control groups has been rare in reactivity investigations to date. The EMA protocol included event-contingent assessments (smoking episodes, urge episodes) and random assessments. Outcomes included biologically confirmed abstinence and self-report measures of withdrawal, self-efficacy, motivation, affect, and temptations. Participants were smokers motivated to quit (N = 96). They were randomized to 1 of 3 groups: EMA for the week preceding a planned quit date, EMA for the week following the quit date, and no EMA. Abstinence rates did not differ between the groups at Day 7 or at Day 28 postcessation. For the 20 subscales assessed at each of 3 assessment times, there were significant differences between participants with and without EMA experience for 3 subscales at the 1st of 3 assessment times, and significant differences for 3 different subscales at the 3rd assessment time. These differences suggest some reactivity to EMA, although the inconsistent pattern across time indicates that further research is needed to definitively conclude that EMA induces reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A clustering approach for identifying and quantifying irregularities in interconnection networks

Support for arbitrary topologies has become more popular for system-area networks but very little has been done in trying to characterize their behavior and performance. Traditional parameters like diameter and bisection width are not sufficient for characterizing the irregularities that abound in such networks and fail to give much insight into throughput performance. A clustering approach for partitioning a network into clusters of richly-connected regions is proposed as a means of defining two performance-correlated characterization metrics: intercluster bandwidth index and intercluster link-cost index. The two characterization metrics are shown to have a strong correlation to saturation throughput when link and load distribution of a network is imbalanced. Simulation results also show that the clustering algorithm can be applied to a variety of network configurations and traffic scenarios, particularly irregular ones. With the proposed characterization metrics that correlate more strongly with performance, it is possible to classify networks into categories having similar performance.     

Quantification of ageing of ultracapacitors during cycling tests with current profile characteristics of hybrid and electric vehicles applications

The ageing quantification of ultracapacitors in cycle-life tests has been studied. Current profiles and the characteristics of the ultracapacitors used in hybrid and electric vehicle applications are specified and validated. With these profiles, significant self-heating occurs but without exceeding the manufacturers' limits. Thus, ultracapacitors are aged in a short time with the same degradation mechanisms observed in normal use. Ageing evaluation is based on the measurement of the electrical parameter changes. A particular phenomenon is performance recovery during rest periods when power-cycling is interrupted for electrical characterisation. Therefore, an online characterisation procedure was added for more accurate evaluation of the ultracapacitors' ageing. A number of devices from two manufacturers are cycled with different current profiles. The obtained results are presented and discussed.     

A 100-GOPS programmable processor for vehicle vision systems

New generations of automobiles will include driver assistance systems requiring powerful, low-cost processors to handle video/camera applications and to enable fast, convenient application development. Shrinking feature sizes on processors already in development will bring substantial increases in system speed and functionality.     

Wireless security is different

Wireless security requires slightly different thinking from wired security because it gives potential attackers easy transport medium access. This access significantly increases the threat that any security architecture must address. Wireless networking broadcast nature makes traditional link-layer attacks readily available to anyone. Wireless network security based on the IEEE 802.11 standard has received a lot of negative attention, since it is coupled with several design errors and security problems. IEEE 802.11 uses spread-spectrum signaling technology, which the military depends on for secure communications. Newer architectures are becoming available to dramatically increase the security of 802.11-based networks.     

Design of a microstrip filter using multiple capacitively loaded coupled lines

A method to design a microstrip filter has been proposed. The multiple capacitively loaded coupled lines are adopted for the design of the microstrip filter. The filter shows different stopband behaviour with respect to even or odd total number of resonators. The transmission zeros may be located around the lower, higher or both regions of the passband's skirt. The coupling among the capacitively loaded lines can produce another transmission zero particularly in the higher stopband. A bandpass filter and a duplexer utilising these features are designed. The equivalent model is also proposed to illustrate the filter's coupling among these capacitively loaded coupled lines. The design has been verified by experimental results     

Grain growth in a low-loss cold-rolled motor-lamination steel

This article attempts to determine the mechanisms governing the grain growth process that occurs during lamination annealing of a cold-rolled, motor-lamination (CRML) steel. A new simulation approach linking a Monte Carlo model with electron backscatter diffraction (EBSD) scans used as input has been employed to incorporate the effects of crystallographic texture on the simulated grain growth process. The results from the texture analysis and the computer simulation of the grain growth process indicate that both stored energy driven grain growth and anisotropic grain boundary growth influence the overall grain growth occurring during lamination annealing.