Vadim V. Silberschmidt

Bio: Vadim V. Silberschmidt is an academic researcher from Loughborough University. The author has contributed to research in topics: Machining & Materials science. The author has an hindex of 44, co-authored 543 publications receiving 8619 citations. Previous affiliations of Vadim V. Silberschmidt include University of Rhode Island & Universities UK.

Thermo-mechanical damage accumulation during power cycling of lead-free surface mount solder joints

Abstract: It is well known that in surface mount technology (SMT), thermal strains in electronic assemblies are induced in the solder joints by the mismatch between the coefficients of thermal expansion (CTE) of the components, substrate and solder, both during their processing and in service. Therefore, thermo-mechanical damage is likely to occur in the solder and the principle reliability hazard in SMT assemblies is the resulting fatigue cracking of the solder fillet, caused by cyclic thermal stresses. These stresses may be caused by both cyclic variations in power dissipation within equipment and by external environmental temperature changes. Most work reported to date has focused on the effects of environmental temperature changes, although for many types of equipment power cycling may result in significant stresses. The present paper describes the experimental determination of the actual temperature distribution in a chip resistor assembly when it is powered. The paper also discusses the significance of such experimentally determined non-uniform temperature distributions in electronic assemblies to fatigue damage accumulation due to both power cycling and to cyclic variations in the ambient temperature whilst the chip resistor is powered. This fatigue damage accumulation study is carried out using finite element analysis.

TEM Microstructural Analysis of As-bonded Copper Ball Bonds on Aluminum Metallization

Abstract: In this study, the nano-scale interfacial details of ultrasonic copper ball bonding to an aluminum metallization in the as-bonded states were investigated using high resolution scanning/transmission electron microscopy with energy dispersive spectroscopy. Our results showed that ultrasonic vibration swept aluminum oxide and copper oxide in some regions of contacting surface, where an approximate 20 nm Cu-Al intermetallics (i.e. CuAl2) formed. In the regions where oxide remained, aluminum oxide layer connected with copper oxides layer. No nano-level voids or gaps were observed at the central area of the interface, including the regions with oxide. Calculation of interfacial temperature showed that the ultrasonic vibration increased the flash temperature up to 465°C which was believed to improve the interdiffusion for the formation of Cu-Al intermetallics.

Finite Element Modeling and Analysis of Ultrasonically-Assisted Drilling of Bone

Abstract: Drilling in bone is a common surgical procedure in orthopedics for fixation and reconstructive surgeries. Research in this area is largely focused on investigating alternate drilling techniques for minimal destruction to the bone tissue. This study measured temperature and force generated during conventional drilling (CD) and ultrasonically-assisted drilling (UAD) using Finite Element (FE) simulations. Three-dimensional FE model of bone drilling was developed and analyzed to simulate the dynamic processes involved in the process. Numerical simulation predicted lower drilling force and temperature in UAD compared to CD using controlled ultrasonic parameters (frequency -- 20kHz, amplitude = 10 micrometers). Drilling tests are performed on fresh bovine femur using surgical drills in the presence of ultrasonic vibrations imposed on the drill in the cutting direction. Force and temperature generation at various depths are calculated and compared for the prescribed drilling techniques. The results obtained from numerical simulations are compared with bone drilling experiments.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Effect of Temperature

Abstract: A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.