Tin Whisker Electrical Short Circuit Characteristics Part 2

Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has a currently unknown probability associated with it. Due to contact resistance electrical shorts may not occur at lower voltage levels. In this experiment, we study the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From this data we can estimate the probability of an electrical short, as a function of voltage, given that a free tin whisker has bridged two adjacent exposed electrical conductors. In addition, three tin whiskers grown from the same Space Shuttle Orbiter card guide used in the aforementioned experiment were cross-sectioned and studied using a focused ion beam (FIB)

Developing an Empirical Model for Estimating the Probability of Electrical Short Circuits from Tin Whiskers

To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish

Estimating the Probability of Electrical Short Circuits from Tin Whiskers

To comply with lead-free legislation, many manufacturers have converted from tin-lead to pure tin finishes of electronic components. However, pure tin finishes have a greater propensity to grow tin whiskers than tin-lead finishes. Since tin whiskers present an electrical short circuit hazard in electronic components, simulations have been developed to quantify the risk of said short circuits occurring. Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that had an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish

Tin Whisker Electrical Short Circuit Characteristics

Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish

Simple equations to predict concentric lower-body muscle power in older adults using the 30-second chair-rise test: a pilot study

Although muscle power is an important factor affecting independence in older adults, there is no inexpensive or convenient test to quantify power in this population. Therefore, this pilot study examined whether regression equations for evaluating muscle power in older adults could be derived from a simple chair-rise test. We collected data from a 30-second chair-rise test performed by fourteen older adults (76 ± 7.19 years). Average (AP) and peak (PP) power values were computed using data from force-platform and high-speed motion analyses. Using each participant’s body mass and the number of chair rises performed during the first 20 seconds of the 30-second trial, we developed multivariate linear regression equations to predict AP and PP. The values computed using these equations showed a significant linear correlation with the values derived from our force-platform and high-speed motion analyses (AP: R = 0.89; PP: R = 0.90; P < 0.01). Our results indicate that lower-body muscle power in fit older adults can be accurately evaluated using the data from the initial 20 seconds of a simple 30-second chair-rise test, which requires no special equipment, preparation, or setting

Smart Control of Fleets of Electric Vehicles in Smart and Connected Communities

The increasing deployment of electric vehicles (EVs) across the United States has introduced many new opportunities and challenges with regards to energy management and control. In smart and connected communities (SCCs), where advanced communication infrastructures are in place, optimal coordination of EVs can significantly impact EV owners, power systems, and charging station owners. This paper develops two scheduling frameworks (static and dynamic) for optimal coordination of a fleet of cooperative EVs in a community with many charging stations and potentially different types of chargers (e.g., level 1, level 2, and DC fast). The scheduling problems are formulated as mixed-integer multi-objective optimization models and then multi-objective solution methods are utilized to find the optimal solution for each of the two scheduling frameworks. Numerical experiments simulated based on the State of Florida verify the usefulness of smart charging for better energy management and satisfying key players' objectives and constraints

Design of an industrial flexible robot controller using matlab

The main objective of this work is to investigate a causal inverse dynamics of a flexible single hub-arm system with a variable tip mass and to control the end point motion. The joint trajectory was assumed and the end point trajectory was obtained directly through the solution of the inverse dynamic problem. Although the flexible link is nonminimum phase in nature, the use of feedforward torque with end point acceleration feedback gives very good performance specially for variable tip mass. A robust controller was designed for tracking the desired trajectory based on classical control methodologies

Solving the Multivariant EV Routing Problem Incorporating V2G and G2V Options

In the near future, gasoline-fueled vehicles are expected to be replaced by electrical vehicles (EVs) to save energy and reduce carbon emissions. A large penetration of EVs threatens the stability of the electric grid but also provides a potential for grid ancillary services, which strengthens the grid, if well managed. This paper incorporates grid-to-vehicle (G2V) and vehicle-to-grid (V2G) options in the travel path of logistics sector EVs. The paper offers a complete solution methodology to the multivariant EV routing problem rather than considering only one or two variants of the problem like in previous research. The variants considered include a stochastic environment, multiple dispatchers, time window constraints, simultaneous and nonsimultaneous pickup and delivery, and G2V and V2G service options. Stochastic demand forecasts of the G2V and V2G services at charging stations are modeled using hidden Markov model. The developed solver is based on a modified custom genetic algorithm incorporated with embedded Markov decision process and trust region optimization methods. An agent-based communication architecture is adopted to ensure peer-to-peer correspondence capability of the EV, customer, charging station, and dispatcher entities. The results indicate that optimal route for EVs can be achieved while satisfying all constraints and providing V2G ancillary grid service

A computerized dynamic biomechanical model of the human shoulder complex

This study introduces a generalized three dimensional dynamic model of the human shoulder complex. This model can be used to analyze load sharing between the muscles, the bones and the ligaments of the shoulder region at any position under any loading conditions. The model was applied to predict the musculoskeletal forces during manual lifting tasks. The MATLAB optimization toolbox was utilized in computing the musculoskeletal forces in the shoulder region. The effects of load and lifting technique on 24 muscle groups, during manual lifting of loads from floor to table height, were investigated