Fred Barez

Thermal characterization of Fan-in Package-on-Packages

The 3D market continues to be driven by mobile applications. The technology integrates devices or packages in the vertical direction to achieve reduction in size and cost along with high performance, challenging IC package designers to maintain a low enough junction temperature without using fans and heat sinks. The study carried out in the paper investigates the effect of design criteria on the thermal performance of a new generation of stacked packages, called Fan-in Package-on-Packages (FiPoPs). The main goal of the undertaken project was to investigate the change in thermal performance in the test model due to variation in the internal thermal design parameters only. Based on the research of earlier generation models, the parameters chosen to analyze in this work included (a) number of thermal vias (b) solder ball I/O density and (c) die size. Due to limited design information pertaining FiPoPs, geometrical and materials parameters for a typical FiPoP were acquired from Statschippac, Inc. This stacked package within FiPoP chosen for analysis included two metal layers, 14 × 14 mm body size, 9 mm × 9 mm die size, 0.075 mm thickness for both top and bottom packages and 0.5 mm solder ball pitch. The results presented by the study show that the thermal resistance of the bottom package of a FiPoP decreases with increase in number of thermal vias and solder balls placed under the package. The decrease in thermal resistance with addition of thermal vias alone is small; solder balls must be added as well to result in significant improvement. As expected, the thermal resistance of the entire package increases as the die size drops.

Dynamic Force Response of Human Legs due to Vertical Jumps

Jumping is a natural exertion that occurs during a variety of human activities including playing sports, working, skateboarding, dancing, escaping from hazardous events, rescue activities, and many others. During jumping, the ankles in particular are expected to support the entire body weight of the jumper and that may lead to ankle injuries. Each year hundreds of patients are treated for ankle sprains/strains with ankle fractures as one of the most common injuries treated by orthopedists and podiatrists. The knee joint is also considered the most-often injured joint in the entire human body. Although the general anatomy of the lower extremities is fairly well understood, an understanding of the injury mechanism during these jumping tasks is not well understood. The aim of this study is to determine the reaction forces exerted on legs and joints due to vertical jumps, through musculoskeletal simulation and experimental studies to better understand the dynamic jump process and the injury mechanism. The joint reaction forces and moments exerted on the ankle, knee and hip joint during takeoff and extreme squat landing of a vertical jump were determined through the application of musculoskeletal simulation. It is concluded that during extreme squat landing of a vertical jump, joint reaction forces and moments were highest in proximal/distal and anteroposterior direction may cause most likely injury to the hip joint ligaments, ankle fracture and knee joint, respectively.Copyright

Optimum spacing of vertical parallel plates for combined natural convection and radiation

The reliability of electronic products depends on their ability to dissipate the heat generated by various components. Application of an array of parallel plates such as a heat sink is a common example of using parallel plates in electronics cooling. The most common practice in dissipation of the heat generated by electronics is by means of natural convection. Others have investigated the optimum spacing of vertical parallel plates for the maximum natural convection heat transfer. The goal of this study is to determine the optimum spacing for the maximum combined natural convection and radiation heat transfer from an array of isothermal parallel plates. An exact correlation was obtained to determine the optimum spacing for the maximum radiation heat transfer alone. It is concluded that the optimum spacing for the combined natural convection and radiation heat transfer is similar to that of the optimum spacing of the natural convection alone. An exact correlation was also obtained to determine the optimum spacing for combined heat transfer.

Load Distribution in Barefoot Running Shoes

Running is one of the most practiced sports around the world and it dates back to Ancient Greece. Running became an Olympic sport in 1896 and today is mostly performed for fun and to stay in shape. Nowadays, athletic shoe companies make claims on the performance of the type of shoes they manufacture. Some of their claims include shoes that allow free movements, fit like a glove, and are in complete harmony with human mechanics. The preceding characteristics are those of so-called barefoot running shoes. Robillard [1] explains that minimalist running shoes could be defined as those that provide limited or no support and only minimal protection, with the heel at the same level as the forefoot. Even though running may have been investigated, however, there is not enough analyses on barefoot running shoes. The objective of this study was to investigate the load distribution on the feet of a healthy running adult wearing barefoot shoes through experimental work and finite element analysis (FEA).The methodology used in this study included experimental as well FEA. Tests were conducted with a 175-lb adult subject wearing a pair of minimalist shoes. Experimental data were collected and used to perform Finite Element Analysis. The barefoot shoes were modeled with an equivalent thickness of 0.453 inch, and the following parameters were experimentally determined such as the Young’s modulus of 467 psi, a density of 0.0025 lb/in3, and a Poisson’s ratio of 0.08.The simulation results yielded a maximum compressive stress of 38.71 psi in the toe region. This stress level was approximately one-half of the stresses generated in the heel region of conventional sport shoes. This study, further, revealed the reduction of stresses at the heel region with barefoot shoes resulting in lower risk of pain and injury to the foot in the absence of impact transients ordinarily experienced with conventional shoes.Copyright

Dependence of Elastic Properties of Human Femoral Cortical Bone on Porosity

Hip fracture is one of the most serious and common health problems among elderly which may lead to permanent disability or death. Hip fracture commonly occurs in the femoral bone, the major bone in the hip joint. Microscopic age-related changes in the structure of cortical bone is one of the factors that is considered to be partially responsible for the increase of fracture risk in elderly. It is of great interest to develop a predictable model of such fractures for the aging population in preparation of a suitable therapy. These micro structural changes influence mechanical properties and, therefore, behavior of bone and are critical to understand risk and mechanics of fracture of bone. Correlation between cortical bone strength and porosity, as a microscopic structural factor, has been examined frequently as a function of age and/or porosity. These studies have investigated the effect of porosity experimentally and have not studied the effect of porosity independently from other structural factors such as bone mineral density. In this study effect of porosity on elastic properties of human femoral cortical bone was studied independently using finite element analysis assuming transversely isotropic behavior in terms of elastic properties with the axis of elastic properties along the longitudinal axis of femur shaft. In this study, published standard mechanical tests for transversely isotropic materials were simulated using finite element computer simulation on models with different porosities. The developed finite element model utilized material properties based on the best fit regression in previously published articles. Pores’ size, shape and distribution were also modeled based on previous experimental studies. The finite element model, in general, predicted behavior of five independent elastic mechanical properties, namely, longitudinal Young’s modulus, transverse poisson’s ratio, transverse shear modulus, transverse Young’s modulus and longitudinal poisson’s ratio, as a function of porosity. Furthermore, effect of porosity on the elastic properties across various age groups was investigated using published data on age-related changes in bone porosity. Mathematical models based on Finite Element Analysis results have been developed using linear least square regression. These models show negative linear relationship between studied elastic properties of human femoral cortical bone and porosity. The Finite Element Analysis results compared well with the previously published experimental data. Furthermore, the results obtained show the elastic properties as functions of age for females and males. The predicted values for elastic properties are lower for men compared to women of age 20 to 40 years old. However, after the age of 44, elastic properties of femoral cortical bone for men are higher than women. The Finite Element Model developed in this study will help to create a clinical bone model for the prediction of fracture risk or the selection of suitable therapy in orthopedic surgery.Copyright

Optimum Spacing of Vertical Parallel Plates for Maximum Radiation Heat Transfer

The reliability of the majority of electrical and electromechanical systems depends on their ability to dissipate heat generated by their internal components. Application of parallel plates for cooling electronic equipment is one of the most common methods of heat dissipation through convection and radiation. Others have investigated the optimum spacing between vertical plates for the case of maximum natural convection heat transfer. The goal of this study was to determine the optimum spacing for the maximum radiation heat transfer.Analytic calculations were carried out to determine the optimum spacing. A mathematical interpolation was used to simplify the view factor correlations and from this an exact correlation was obtained to determine the optimum spacing for radiation heat transfer. It was concluded that for a known plate surface area, the optimum spacing for the maximum radiation decreases when the ratio of height over length of the plates increases. For fixed geometric parameters, the optimum spacing for radiation will display a skewed parabolic distribution when the surface emissivity of the plates was increased.Copyright

Factors Contributing to Spiral Humerus Fracture During Muscle-Up Exercise

Spiral humerus fractures associated with extreme muscular torsion loading have been well documented in literature. Throwing motions and arm wrestling are the two causes most often researched, while spiral fractures associated with gymnastics have received less attention. The purpose of this study is to explore the factors that may contribute to torsional failure of the humerus while performing a gymnastics move known as a muscle-up. Primary motivation for this study was the result of the author sustaining a spiral fracture to the distal aspect of her left humerus while attempting a muscle-up. To the author’s knowledge, no previous studies analyzing the forces imposed on the upper extremities during a muscle-up have been conducted.Utilizing the author’s estimated anthropometric measurements and the kinematic and kinetic constraints of the muscle-up activity, the torque acting about the long axis of the humerus was determined in two ways. First, an analytical approach was used to calculate the forces and moments within a simplified linkage representation of the upper extremity for several representative muscle-up postures. The second method was a computer simulation that modeled the entire body with muscles in several different kinematic positions and outputted internal body elbow joint net moments.The analytical approach resulted in torques between 12.0 N·m and 29.3 N·m. The kinetics derived with the computer simulation revealed joint reaction torques between 13 N·m and 38 N·m and net axial torques between 29.1 N·m and 69.1 N·m acting on the left humerus. The internal moments predicted using the computer simulation were above the author’s minimum predicted torque, 53 N·m, associated with humerus fracture initiation.Although there may be many factors that contribute to spiral humerus fracture, in this study, it was determined that the kinematic positions of the muscle-up movement are sufficiently extreme so as to produce torques capable of resulting in spiral humerus fracture.Copyright

Dynamic Response of Human Legs due to Horizontal Jump

Jumping is a coordinated extension of the human body through combined strength and agility to perform a leap motion far enough for the feet to land on the ground. However, the repeated reaction forces and the resulting stresses on the ankle, knee and hip joints may cause injuries to a person. A primary mechanism of such injuries is suggested to be the acute high impact loads experienced during the landing in a horizontal jump. The goal of this study is to determine the reaction force distribution at the joints in the lower extremities during the horizontal jump. A detailed biomechanical system was constructed to calculate the reaction forces generated during the horizontal jump. The horizontal jump kinematics of a participant was measured using a three-dimensional motion capture system and the landing forces were measured using two force plates. Biomechanical simulation software was used to calculate the internal joint reaction forces at the ankle, knee, and hip. It was determined that the maximum reaction forces primarily occurred in the proximo/distal direction of the hip, 2,300 N; and ankle, 2,700 N. However, at the knee joint, the maximum reaction force was determined to be in antero/posterior direction, at 2,000 N; and proximo/distal direction, at 2,100 N, respectively.Copyright

Cooling System for a Portable Bio-Industry Centrifuge

A centrifuge is used in bio-industry to separate species in blood and other chemicals. Bio-industry requires a temperature of zero degree centigrade in the rotor compartment of a centrifuge where samples are placed. In general, the current portable centrifuge systems generate a temperature of about 22 °C in the rotor compartment when operating at 3000 RPM. The motor and the electronics are the primary sources of the heat generation in such centrifuge. The aim of this study is to develop an appropriate cooling system for a specific portable centrifuge used in separating bioparticles that generates a total heat of approximately 43 W. Experimental, analytical and computer simulation were employed to achieve the project objective of reducing and maintaining the rotor compartment temperature at zero degree C. The CFD code Simulation model predicted rotor compartment temperatures that were in good agreement with those of the experimental measurements within 3%. Having confidence in the CFD model, simulation was carried out to incorporate four TEC units that are embedded on the surface of the rotor compartment resulting in reduced temperature to zero degree C.Copyright

A New Approach to Model Axial Fans in Commercial CFD Tools

Most commercial CFD tools use fan curves to represent a fan. However, the presence of a blockage near inlet or exhaust of a fan and a restricted airflow direction will alter the fan performance, and the use of the original fan curve may result in erroneous results in these cases. A new approach to model fans will be presented in this paper. Using conservation of mass, momentum and energy, and the velocity triangles, this model relates velocity and pressure at fan exhaust to the corresponding values at fan inlet as well as fan geometry, rotational speed and fan blade lift and drag coefficients.Copyright