A Novel Mechanism of Embrittlement Affecting the Impact Reliability of Tin-Based Lead-Free Solder Joints

This work addresses a new mode of brittle failure that occurs in the bulk of tin-based lead-free solder joints, unlike the typical brittle failures that occur in the interfacial intermetallics. Brittle failures in the joint bulk result from the low-temperature ductile-to-brittle transition in the fracture behavior of β-tin. The bulk embrittlement of these joints is discussed by referring to the results of impact tests performed on both solder joints and bulk solder specimens. The mechanism of bulk embrittlement is largely explained based on the results of a fractography study performed on the bulk joint failures using scanning electron microscopy.     

Detection of failure sites by focused ion beam and nano-probing in the interconnect of three-dimensional stacked circuit structures

Focused ion beam (FIB) and nano-probing were applied for failure analysis of three-dimensional stacked circuits with copper through-silicon-vias between the stacked chips. The failure analysis was done after high temperature storage and thermal cycling tests. Passive voltage contrast in FIB allowed to pinpoint the open sites. FIB cross-sections showed the presence of opens at the bottom of the copper vias. The failure cause was suspected to be an interlayer particle, which was confirmed by optical profilometry. Nano-probing was used on another sample to pinpoint the failure location through the measurement of the local resistance within the daisy chains. The failure was traced out to be related with surface contamination.     

Trade-off analysis on cost and manufacturing technology of an electronic product: Case study

A trade-off analysis on the cost and system packaging metrics of an electronic product aimed at the commercial/retail industry has been carried out. By comparing the system cost and packaging metrics with those of comparable consumer products, we have determined that there is opportunity for significant cost, size, and weight reduction of the overall electronics packaging system. These include the use of fine pitch IC packages, smaller discrete components, denser PCB wiring technology, double sided IC package surface mount, surface mount connectors, and improved plastics for the product housing. The analysis concluded that PCB area reduction of 40%, using a single PCB instead of three boards, reduction in board cost of over 50% and product weight reduction of over 28% are possible using available technologies.     

Control over the parameters of InAs-GaAs quantum dot arrays in the Stranski-Krastanow growth mode

The effect of the growth temperature on the density, lateral size, and height of InAs-GaAs quantum dots (QD) has been studied by transmission electron microscopy. With the growth temperature increasing from 450 to 520°C, the density and height of QDs decrease, whereas their lateral size increases; i.e., the QDs are flattened. The blue shift of the photoluminescence line indicates decreasing QD volume. The observed behavior is in agreement with the thermodynamic model of QD formation. The effect of lowering the substrate temperature immediately after the formation of QDs on the QD parameters has been studied. On lowering the temperature, the lateral size of QDs decreases and their density increases; i.e., the parameters of QD arrays tend to acquire the equilibrium parameters corresponding at the temperature to which the cooling is done. The QD height rapidly increases with cooling and may exceed the equilibrium value for a finite time of cooling, which enables fabrication of QD arrays with a prescribed ratio between height and lateral size by choosing the time of cooling.     

Formation of dislocation defects in the process of burying of InAs quantum dots into GaAs

Evidence given by electron microscopy of dislocation relaxation of stresses near InAs quantum dots buried into GaAs is presented. It was found that dislocation defects not emerging to the film surface are formed in some buried quantum dots. This suggests that stress relaxation occurs in the buried state of the quantum dot, rather than at the stage of the formation and growth of an InAs island on the GaAs surface. Models of internal dislocation relaxation of buried quantum dots are presented.     

Exploiting Varying Resource Requirements in Wavelet-based Applications in Dynamic Execution Environments

In the context of future dynamic applications, systems will exhibit unpredictably varying platform resource requirements. To deal with this, they will not only need to be programmable in terms of instruction set processors, but also at least partial reconfigurability will be required. In this context, it is important for applications to optimally exploit the memory hierarchy under varying memory availability. This article presents a mapping strategy for wavelet-based applications: depending on the encountered conditions, it switches to different memory optimized instantations or localizations, permitting up to 51% energy gains in memory accesses. Systematic and parameterized mapping guidelines indicate which localization should be selected when, for varying algorithmic wavelet parameters. The results have been formalized and generalized to be applicable to more general wavelet-based applications.     

Effects of continuous and intermittent self-monitoring on academic behavior.

Conducted a project with 27 undergraduate Ss dealing with review preparation for the general aptitude portions of the Graduate Record Examination. A linear teaching machine programed with quantitative and verbal problems was employed. The Ss were randomly assigned to 4 conditions: (a) continuous self-monitoring, (b) intermittent self-monitoring, (c) performance feedback, and (d) control. Self-monitoring Ss were instructed to record their progress by pressing a counter on either a continuous or intermittent schedule following correct answers. Performance-feedback Ss received information on the accuracy of their responding but were not given the opportunity to self-monitor. Control Ss received neither self-monitoring instructions nor performance feedback. Results show that self-monitoring Ss remained for significantly longer review sessions and that this effect was more pronounced under the continuous rather than the intermittent schedule. Self-monitoring Ss also displayed significantly better accuracy on quantitative problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Female counselor–client dyads: Effects of counselor age, client marital status, and intimacy level of presenting problem on perceptions of counselors.

Explored the impact of counselor age, level of intimacy of clients' presenting problems, and client marital status on perception of counselors and the counseling relationship with 48 married females (mean age 21.9 yrs) and 48 unmarried females (mean age 26.3 yrs). Ss viewed a series of 3 videotapes, which were counterbalanced for level of intimacy of client's presenting problems and depicted initial interviews between young female clients and either younger or older female counselors. After viewing each individual vignette, Ss completed a counselor rating form, a client satisfaction form, and manipulation checks for presenting problem intimacy and counselor age. Overall, differences in presenting problems and counselor age were perceived as intended. Ss' marital status was unrelated to any measures. Counselors were judged as most expert, attractive, and trustworthy when dealing with presenting problems that were least intimate. Ss anticipated greater satisfaction with younger rather than older counselors only for the least intimate presenting problem. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Non-Gaussian Air Gap Response Models for Floating Structures

The air gap response of a specific semisubmersible platform subjected to irregular waves is considered. Statistical analyses are performed on model test data for the absolute near-structure wave elevation, and these measured data are compared with predictions resulting from probabilistic models. Models applied are first-order and second-order diffraction models typical of standard practice, and two new hybrid models that include second-order effects in the incident wave, but not in the diffracted wave. The first of these hybrid models is moment based, while the second relies on narrow-band random process theory. Either of these new models can be implemented in place of the standard linear-only model with little additional computational effort, as only linear diffraction analysis is required. Both new models are found to better predict the air gap demand than standard linear diffraction analysis.