James H. Constable

Electrical resistance as an indicator of fatigue

The dependence of the electrical resistance on strain and fatigue was analyzed for the case of electrical interconnections subjected to a sinusoidal strain. Measurements of the resistance change at the drive frequency and at twice the drive frequency provided greater sensitivity than static resistance measurements. Equations were developed to model the electrical resistance to second order in the strain. The resistance change gives a direct measure of the interconnect strain. The amplitude of the resistance change at twice the drive frequency was found to increase rapidly with fatigue. The ratio of the resistance change at twice the drive frequency to the change at the drive frequency was approximately 20% at low cycle fatigue failure. The ratio was suggested as a fatigue indicator for reliability analyses or for accelerated testing. >

An investigation of solder joint fatigue using electrical resistance spectroscopy

Interconnect electrical resistance is examined as a possible bases for a reliability tool. Measurements are reported of the resistance change of lap shear (60% Sn-40% Pb) solder joints as a function of fatigue. The expected dependence of electrical resistance on elastic strain, plastic deformation, and cyclic fatigue is reviewed. An analytical framework is developed to examine the observed electrical resistance change. A technique called resistance spectroscopy was used to measure the small resistance change resulting from the strain and fatigue in the presence of much larger resistance changes resulting from temperature and other fluctuations. The level of the noise in the resistance measuring system used for the lap shear joints was less than one nano-ohm. The lap shear solder joints exhibited a systematic resistance change as the specimens were cycled toward failure. Initially the average resistance increased, followed by a much stronger decrease, and lastly increased markedly as crack propagation began. The decreasing-resistance portion of this signature occurs prior to crack initiation, and can be used to detect incipient solder joint failure more quickly and with greater ease than present techniques. >

AMLCD flicker model considering the V/sub T/ shift in a-Si:H TFT

The observed development of flicker with time in active matrix liquid crystal display (AMLCD) panels has been correlated to the threshold voltage shift of the thin film transistors (TFTs) used in panels. The effect of a threshold voltage shift on the panel flicker was calculated using a flicker model developed here. One set of AMLCD panels used for the flicker characterization employed top-gate TFTs, while a second set employed bottom-gate TFTs. Optical measurements to determine the flicker voltage as a function of aging were performed on both types of panels. Electrical characterization of the TFTs extracted the threshold voltage from the C-V measurement. Samples of the TFTs were available on the kerf strips for both panel types, and ensured that the optically characterized panels and the TFTs electrically characterized were manufactured in the same batch for each of the two panel types.

Heat pulse transmission from sodium fluoride into helium I

Heat pulse transmission across a NaF-He I interface reveals behavior not observed at a He II interface. Longitudinal and transverse crystal modes are resolved at the detector with the longitudinal pulse exhibiting a unique characteristic structure. The detected longitudinal pulse appears with an initial overshoot lasting about 100 nsec and a reduced rear portion lasting the duration of the input pulse. The initial overshoot component echoes repeatedly between opposite surfaces of the crystal, and is indicative of the small transmission predicted by the acoustic mismatch theory. No echoing of the rear portion has been observed, and apparently the rear portion has a different coupling process at the interface. For the transverse pulse, a change in shape and a delay in arrival time are noted upon transmission into liquid, suggesting that certain portions of the pulse are not transmitted. Measurements of the amplitude dependence of the various pulses are made, and compared with a model having a frequency-selective coupling at the interface.

Acoustic Emission Analysis for FatiguePrediction of Lap Solder Joints inMode Two Shear

This current research method combined the disciplines of Fractography, ConFocal analysis, and Acoustic Emission to discover and identify failure modes of eutectic (62%Sn36%Pb2%Ag) solders (with and without rosin core flux) and lead free (99CSn-Cu) solder under cyclic displacement controlled Mode II shear fatigue. Results show a strong pattern of acoustic emission correlating to stages of failure. Three distinct stages were found: “Stage I” (crack initiation), “Stage II” (nucleation), and “Stage III” (failure and/or propagation). Time domain analysis shows distinct waveforms for each stage of fatigue. The frequency domain analysis shows a distinct pattern in the PSD. The combination of these two trends allows for a basis to predict solder joint fatigue in an acoustical manner utilizing acoustic emissions. Fractographic results support the trends seen in the acoustic emission analysis for each stage of fatigue. Dominant failure modes of specimens appeared to be intermetallic crack growth, grain coarsening, and dislocation energy effects. These failure modes can be explained in both the time and frequency responses of these specimens. The conclusion is that utilizing acoustic emissions with the disciplines of Acoustic Emissions, Fractography, ConFocal analysis has uncovered and identified failure modes of eutectic (62%Sn36%Pb2%Ag) solders (with and without rosin core flux) and lead free (99CSn-Cu) solder under cyclic displacement controlled Mode II shear fatigue.

Production of H atoms in solid H2 by RF discharge

Hydrogen atoms have been produced by RF discharge at the surface of an H2 crystal and studied by ESR techniques. The mean concentration at 4.2 K was estimated to be 1015 atoms per cm3 for about 14 h of source pulsing. This atom concentration was shown to be stable for long times. The results suggest that diffusion of atoms into the interior of the solid takes place very rapidly.

Investigation of Environmental Noise in Small Electrical Conductors

Large excess resistance noise has been observed in small conductors surrounded by air. The conductor resistance was found to have a well-defined average power spectral density over the observed frequency range from 10-4 to 200 Hz and the dependence of the noise was measured as a function of bias current, temperature, temperature coefficient of resistance (TCR), spatial correlation, and state of the surrounding air. In this paper, three different mechanisms were identified that produce the noise. The room-temperature fluctuations were measured and found to have a spectral density nearly proportional to f-2 over the observed six-order-of-magnitude frequency range. The lowest frequency noise around 10-4 Hz could be predicted from the measured temperature fluctuations using the TCR. Above 10-3 Hz and below 1 Hz, enclosing the wire in a box greatly reduces the noise, and placing the wire in a vacuum eliminates the predominant noise. This noise was directly related to the temperature of the conductor, somewhat proportional to the TCR, independent of bias current, and has a correlation length smaller than the specimen size. The highest frequency noise does not depend on the conductor temperature, TCR, or the presence of air. It had a very strong dependence on bias current and had a long spatial correlation. The mechanism that generates this noise is not understood

Relaxation of in-plane and out-of-plane oH2 pairs☆

Abstract Previous measurements of the nuclear spin-lattice relaxation time for nearest neighbor o H 2 pairs have been analyzed. The analysis has yielded the relaxation time for both in-plane and out-of-plane pair configurations. The relaxation time for the in-plane pairs was found to be 97ms and that for out-of-plane pairs was 12 ms. An analysis of the pair signal amplitude versus time indicated that the equilibrium time constant for the formation of in-plane pairs was over an order of magnitude longer than that for out-of-plane pairs.

Work in progress — Developing an individualized life-long learning plan for junior electrical and Computer Engineering majors

The Accreditation Board for Engineering and Technology (ABET), now ABET Inc., adopted Engineering Criteria 2000 (EC2000) in 1997. At the time this was considered a revolutionary approach to accreditation criteria, because of its focus on what is learned in the classroom rather than what is taught. In the spring of 2003 the faculty of the Electrical Engineering and Computer Engineering department at Binghamton University approved a new course - EECE 382 - Electrical and Computer Engineering Seminar II. The intent was to consolidate topics that were being taught across several courses within one focused seminar to better ensure that Criteria 3 of General Criteria for Basic Level Programs - Program Outcomes and Objectives - was consistently addressed. EECE 382 was to provide an overview of the professional aspects of the fields of Electrical Engineering and Computer Engineering. This paper reports on how one of the objectives of Criteria 3: ‘a recognition of the need for and an ability to engage in life-long learning’ is addressed in EECE 382.

Correlation of the V/sub T/ drift in a-Si:H TFT to the optically observed flicker increase in AMLCD

The observed development of flicker with time in AMLCD panels has been correlated to the threshold voltage shift of the thin film transistors (TFTs) used in the panels. The effect of threshold voltage shift on panel flicker was calculated using a flicker model developed here. One set of AMLCD panels used for the flicker characterization employed top gate TFTs while a second set employed bottom gate TFTs. Optical measurements to determine the flicker voltage as a function of aging were performed on both types of panels. Electrical characterization of the TFTs extracted the threshold voltage from the C-V measurement. Samples of the TFTs were available on kerf strips for both panel types, and ensured that the optically characterized panels and the TFTs electrically characterized were manufactured in the same batch for each of the two panel types.