Effects of the second war Research Paper Example | Topics and Well Written Essays - 1250 words

Effects of the second war - Research Paper Example Such a policy revealed ?an eagerness, a desire, not to hinder the ag- gressors in their nefarious work.? The western powers allowed Germany to have Austria, ?despite the undertaking to defend her independence; they let her have the Sudeten region; they abandoned Czechoslovakia to her fate.? Finally, Stalin enunciated Soviet policy towards its neighbors: We stand for peaceful, close and friendly relations with all neighboring countries which have common frontiers with the U.S.S.R. That is our position; and we shall adhere to this position as long as these countries maintain like relations with the Soviet Union, and as long as they make no attempt to trespass, directly or indirectly, on the integrity and inviola- bility of the frontiers of the Soviet state. He concluded with a warning to the Party ?to be cautious and not to allow our country to be drawn into conflicts by war- mongers who are accustomed to have others pull the chestnuts out of the fire for them.?11 Was Stalin's statemen t a revolution in Soviet foreign policy or was he restating an old hope, agreement with Germany over Eastern Europe? He was probably attempting to warn Britain and France not to leave the Soviet Union to face Germany alone. From Berlin there was silence. Although Ribbentrop brought the speech to Hitler's attention suggesting that he be authorized to learn more about Stalin's intentions, Hitler was uninterested. Alexei Merekalov, the Soviet ambassador, brought a message from the Kremlin to the German Foreign Ministry on April 17. Ostensibly the reason for his visit was the matter of Soviet con- tracts with the Skoda works in Czechoslovakia for war materi- als. However, Merekalov proceeded to lead Ernst von Weizsaecker, the state secretary, into a discussion of German-Polish relations and finally came around to the subject of Russo-German affairs. At last Merekalov got to the point: ideological differences, he suggested, need not be a ?stumbling block? to friendly relations. ?Russia h ad not exploited the present friction between Germany and the western democracies against us [Germany], nor did she wish to do that.?12 There was no reason for Russia and Germany not to enjoy normal relations. In contrast to Weizsaecker's account, according to Soviet doc- uments released in 1990 and 1992, the meeting was not the occasion of a Soviet hint at a possible rapprochement. The signal of detente was coming from the Germans. Merekalov was merely following instructions in presenting Soviet complaints concern- ing Germany's failure to fulfill contracts of the former Czecho- slovak Skoda factories. Merekalov made no plea for improved Russo-German relations. It is quite possible that Weizsaecker's account is the more accurate. Meanwhile, Britain and France embarked on tortuous nego- tiations with the Soviet government. On April 14, the British gov- ernment pressed the Soviet Union to make a public declaration promising to assist any European neighbor of the Soviet Union who resi sted aggression if such assistance was desired. Britain would not be involved in this declaration. France, however, made a different proposal involving France going to war against Germany if Poland or Romania were to be attacked. France would aid the Soviet Union if it were at war as a result of aid- ing Poland or Romania. Litvinov replied on April 17 with a proposal for a triple al- liance in which Britain, France, and the Soviet Union would aid each other in case of aggression against

How people are managed and how they lead Essay Example | Topics and Well Written Essays - 4000 words

How people are managed and how they lead - Essay Example Four of the eight principles are: Congruence not Incongruence, Descriptive not Evaluative, Problem not Person Oriented and Specific not Global. Explain the meaning of the concepts and using ideas from your own experience give examples of their meaning. 3 3. Read the case study and discuss the issues, in terms of supportive communication which it raises. 4 Portfolio Assignment 2 1. House, R.J. in his ‘Path Goal Theory of Leadership’ and Hersey, P. and Blanchard, K.H. in their ‘Situational Leadership Theory’ offer two contingency models of leadership. Discuss, with reference to these two models of leadership the basis upon how leaders engage with their staff to help them improve their performance and gain commitment. 6 2. Discuss the nature and components of transformational leadership. How does transformational leadership differ from the behavioural models of leadership, such as Tannenbaum, R. and Schmidt’s, ‘Continuum Model’ and Contingen cy models of leadership such as the ‘House’ and ‘Hersey-Blanchard’ models discussed above. 7 Portfolio Assignment 3 1. Analysis of the case study 9 2. Research suggests that adults do not follow a well developed set of principles when they make decisions. Discuss how leaders might reflect on  the appropriateness of a decision  in terms of ethical considerations. Give examples to support your answer. 10 Portfolio Assignment 4 1. Resistance to organisational change, particularly when the change is ‘soft’ in nature, can stem from the individual or from the organisation. Discuss the nature of, and explore the reasons why, change is often resisted. 12 2. From a management perspective how can this resistance be overcome? 13 References 14 Bibliography 17 Portfolio Assignment 1 Whetten and Cameron (2011, p261) citing Bowman (1964) write that, â€Å"Surveys have consistently shown that the ability to effectively communicate face to face is the char acteristic judged by managers to be the most critical in determining promotability†. 1. One way to improve communication is through ‘Supportive Communication†. Discuss what Whetten and Cameron mean when they define this concept of communication. Why do they consider it so important? The term ‘supportive communication’ as used in the book of Whetten and Cameron aims to highlight two characteristics of communication: the potentials of communication to help towards the achievement of the goal set and the freedom provided to both parties in order to state their views (Whetten and Cameron 2011). Supportive communication is a mode of communication that can be quite important in certain organizational events, such as interviews (Whetten and Cameron 2011). Indeed, an interview between a candidate and the employer would have more chances to lead to the development of a successful cooperation if both parties were allowed to show their concerns and their percepti ons in regard to the issues discussed during the interview (Whetten and Cameron 2011). In other words, for Whetten and Cameron supportive communication can be used for enhancing cooperation and trust in the workplace. No other mode of communication, apart from supportive communication, offers to both parties the chance to feel equal, a condition that can be quite crucial in certain cases; for example, using supportive communication an interviewer can identify the actual willingness of the interviewee to work as a member of a group (Whetten and Came

McWane, Inc. Essay Example for Free

McWane, Inc. Essay McWane, Inc. is a privately held company based in Birmingham, Ala., which owns plants across the country and Canada and who is one of the world’s largest manufacturers of cast iron sewer and water pipe (McWane Mess). From 1995-2003, McWane plants, in the U.S., had 4,600 worker injuries (CBC News). The company was also cited for more than 400 safety violations and 450 environmental violations during that same period (Barstow, Foundry). Tyler Pipe, one of McWane’s plants, was described by one its workers. He said it was â€Å"a dim, dirty, hellishly hot place where men are regularly disfigured by amputations and burns, where turnover is so high that convicts are recruited from local prisons, where some workers urinate in their pants because their bosses refuse to let them step away from the manufacturing line for even a few moments† (Barstow and Bergman, Texas). A federal investigation began in January 2003, which was the same month The New York Times published a series of articles that described McWane as one of the nations most persistent violators of workplace safety and environmental laws (Barstow, Foundry). CAUSES Root organizational causes and regulatory weakness factors contributed to the McWane scandal. The structure at McWane contributed to the scandal because it was one of the root organizational causes. McWane Inc. is a privately held organization where the family and a few close individuals run it. The family is described as secluded and very private (Barstow and Bergman, Family’s). Executives and family members repeatedly decline interview requests and rarely talk to the media (Barstow and Bergman, Family’s). In 2007, of McWane’s twenty-five divisions, only two included McWane in the name (Wisniewski). Even though McWane’s divisions were places where the desperate seek work (Barstow and Bergman, Texas), society did not hold the right people accountable. Many individuals do not know McWane is connected because the plant names rarely reflect their owner. Without interviews, the fact that it is a private company, and that it keeps its name off new divisions, McWane lacks transparency to help keep it accountable. The seclusion and privacy of the family makes it seem as though they stay out of the public eye for a reason. McWane’s organizational culture was also a root cause that contributed to the scandal. One phrase was posted throughout the plants and was posted in large orange print: REDUCE MAN HOURS PER TON (Barstow and Bergman, Texas). This phrase created a culture that drove all aspects of the McWane companies. McWane was not the best place to work. In fact, there were times when turnover was 100 percent at one plant (The McWane Mess). High turnover is one measure of the culture at McWane and it shows how employees fit into that culture. The high turnover was disturbing and not normal for the industry. Acipco, a direct industry competitor, had a yearly turnover of around half a percent (Barstow and Bergman, Family’s). The organizational culture that focused on one key phrase continued into work shifts. There were two 12-hour shifts instead of the normal three shifts of eight hours. At the end of a shift, supervisors often called for four more hours of work. Therefore, employees worked 16-hour days, sometimes seven days a week (Barstow and Bergman, Texas). Leadership was also a root organizational cause. McWane never developed a system to hold supervisors accountable for safety; however, their system for holding supervisors accountable for production downtime (Barstow and Bergman, Texas). Federal rules require conveyor belts be shut off for maintenance. They also require that all belts have safety guards. The rules are important because they help prevent workers from being caught and crushed. In one instance, inspectors discovered that a belt violated both of those rules (Barstow and Bergman, Texas). This negligence contributed to one of the nine deaths that occurred at McWane divisions from 1995-2003 (Barstow and Bergman, Deaths). Leaders in the company gave orders that were in clear violation of laws. Another example of leadership was what to do with 200 old tires. It would have cost about $750 to have them brought to a waste dump. However, documents show that a plant manager ordered the tires be burned, even though he had been notified burning tires violated air-quality laws (Barstow and Bergman, Texas). The managers like the one above were partially victim to those higher up. The leadership style at McWane was clearly a top down approach. One plant manager stated, â€Å"I was like a robot. All that mattered was getting machines moving again after an accident† (The McWane Mess). One risk manager says that a top down approach creates a disconnection between plant managers and executives. He also explains that this disconnection increases in privately held companies due to a lack of accountability (The McWane Mess). OSHA’s regulatory and oversight weakness contributed to the McWane scandal. At the time, the laws in place were not severe enough detour McWane from committing them. At the time of the scandal, the crime, of willfully violating safety rules that cause the death of a worker, was a misdemeanor. That crime was a less serious than harassing a wild burro on federal lands, which was punishable by up to one year in prison (Barstow and Bergman, Deaths). The fines McWane had to pay for violations were lower than the cost of having the machines down due to implementing and following safety regulations. A McWane executive confessed that Tyler Pipe had willfully ignored workplace safety laws, a crime that caused the death of a worker. The company only paid a $250,000 fine (The McWane Mess). OSHA let off McWane through payments and it did not do more to ensure the safety of workers in McWane plants. Weak labor union oversight also played a role in contributing to the scandal. The labor unions that represented McWane workers were usually small and overwhelmed with cases. The unions had no bargaining power because they were small, so they could not effectively protect their workers from low wages, hours per shift, or dangerous environments. A United Steelworkers union official attempted to tour Tyler Pipe with a safety and health specialist but had been rejected twice (The McWane Mess). CONSEQUENCES McWane scandal had widespread consequences. Those consequences affected the company as well as the environment and manager at the plants. The scandal produced financial woes and a tainted reputation for McWane. McWane was ordered to pay $19 million in fines and restitution in 2006 (Barstow, Foundry). In addition, McWane was ordered to pay $8 million in fines for dozens of workplace safety and environmental crimes in 2009 (Barstow, Iron Pipe). The fines that McWane had to pay were substantially more than any other fines it had previously received. The McWane scandal also greatly affected the environment. As stated before, McWane had over 450 environmental violations (Barstow, Foundry). One of those incidents, the burnt tires, caused toxins to be released directly into the air. Another incident that McWane was charged with was illegally dumping oil into the Atlantic Ocean. McWane had dumped so much oil that it created an 8.5-mile-long slick (Barstow and Bergman, Family’s). Lastly, the McWane scandal affected the lives of those managers who were charged criminally. Four McWane plant managers were convicted or pled guilty to committing environmental crimes (United States v. Atlantic). These people took risks that ended in tarnished reputations, criminal records, jail time, and hefty fines. PREVENTION Prevention is key so that scandals, like McWane, do not happen again. One preventative step is that the government has set stronger penalties for companies who repeatedly violate safety and environmental laws. The government has also set out better guidelines to prosecute repeat offenders (Barstow, Guilty Verdicts). Another preventative measure is that OSHA is looking to increase its criminal enforcement arm. In four years, OSHA only sent 21 percent of eligible cases to the Department of Justice, and the DOJ acted on 4 percent (McGarity et al). If OSHA can increase its force, it can ensure the safety of more workers. The increased force would be a deterrent for companies, because the chances of it being charged would increase. One last way to prevent other scandal is to have the White House and Congress step up (McGarity et al). If these two groups could work together and provide OSHA with a larger budget, OSHA could then improve everything that they do. It all comes down to the fact that OSHA is there for the people, but with a small budget, they cannot do the best job possible. Works Cited Barstow, David, and Lowell Bergman. At a Texas Foundry, an Indifference to Life. The New York Times 8 Jan. 2003. Print. Barstow, David, and Lowell Bergman. Deaths on the Job, Slaps on the Wrist. The New York Times 10 Jan. 2003. Print. Barstow, David, and Lowell Bergman. Familys Profits, Wrung From Blood and Sweat. The New York Times 9 Jan. 2003. Print. Barstow, David. Foundry Pleads Guilty to Environmental Crimes. The New York Times 23 Mar. 2005. Print. Barstow, David. â€Å"Guilty Verdicts in New Jersey Worker-Safety Trial.† The New York Times 27 April 2006. Print. Barstow, David. Iron Pipe Maker Is Fined $8 Million for Violations. The New York Times 25 Apr. 2009. Print. CBC News: The Fifth Estate A Toxic Company The Canadian Connection. CBCnews. CBC/Radio Canada, 8 Jan. 2003. Web. McGarity, Thomas, Rena Steinzor, Sidney Shapiro, and Matthew Shudtz. Workers at Risk: Regulatory Dysfunction at OSHA. The Center for Progressive Reform. Feb. 2010. Web. The McWane Mess. ISHN Magazine. BNP Media, 11 Feb. 2010. Web. United States v. Atlantic States Cast Iron Pipe Company Et Al. Fact Sheet. EPA. Environmental Protection Agency, 9 June 2011. Web. Wisniewski, Barbara J. The McWane Story. McWane, 2012. Print.

Descriptive Writing Essay Example for Free

Descriptive Writing Essay I could feel a gentle warm breeze that was blowing in from the west, bringing with it a mouth-watering smell of strawberry ice cream. Also with the wind came the enchanting smell of fresh salty air mixed with another smell that I didn’t recognise. The active bustling metropolitan was surrounded by rolling emerald green hills, giants watching over me. In the centre of the city sat a colossal thirty storey skyscraper made purely out of glass and reinforced steel. The city faced the never ending topaz sea: it stretched all the way up to a calm and pleasant lake which glittered over a mile away in the distance. The north section of the city was taken up by imposing skyscrapers and a humming metropolitan of lights and music; a huge building encrusted completely with multi-coloured gems that bathed the city in the reflective luminosity. Nestled at the bottom of the skyscrapers were dozens of magnificent and completely unique cafe’s and bars. The first cafe at the top was a marble building that looked like a mausoleum, with heavy columns. The second bar was completely different- a million lights flashed from every surface. The third cafe was a long, low building with the front made completely of glass that was patterned with hundreds of different patterns, and it had beanbags inside and low coffee tables. Another cabin was covered in flowers that had grown on the walls and doorway and another spectacular cabin was made of solid gold that seemed to glow in the sunlight.

Effect Of Vibration On Solder Joint Reliability Engineering Essay

Effect Of Vibration On Solder Joint Reliability Engineering Essay CHAPTER 01 INTRODUCTION SOLDER JOINT IN ELECTRONIC ASSEMBLIES Circuit boards range from simple single moulded plastic boards with copper conductors on one or both sides to multilayer boards with copper conductors, each layer being separated by a dielectric and interconnected by metal conductors. Minimum line width and spacing between lines is less than 100  µm. The board typically is made from a composite such as an epoxy with layered sheets of woven fibreglass. The dielectric material between layers of conductors is usually a polymer, for example polyimide. To maintain solder ability, the exposed copper may be coated with an inhibitor such as benzotriazole or with a solder overcoat. Components are attached to the board with solder or metal-filled conductive adhesives. Fully assembled boards may be further protected against moisture, contamination, and mechanical damage by a cover coat. 1.2 SOLDER JOINT RELIABILITY AND FAILURE Solder joints are widely used in the electronic packaging industry to produce good electrical, thermal, and mechanical connections between the package and the printed circuit board. Eighty percentage of the mechanical failure in airborne and automation electronic caused by vibration and shock. Design appropriate measure to ensure the survival equipment in the shock and vibration environment is necessary to do so. Remaining 20 percentage of mechanical failure related to thermal stresses resulting from high thermal gradients, coefficient of thermal expansion and high coefficient of elasticity. Solder joint failure occur in several reasons: Poor design of the solder joint A bad solder joint treatment Solder material Excessive stress applied to solder joints. In general, however, the solder joint failure are simply ranked according to the ature of stress that have caused. Most joint failure fall into three major categories: Fatigue failure due to cyclic stress application Due to the implementation of a long term or permanent load The stress is due to overloading in the short term Reflow profile also has a significant role on solder joint reliablity. because It also has a high influence micro structure of the solder joint. Vibration failure of solder joints is often assessed for reliability using high accelerated life test, which is represented by a GRMS- time curve. For surface mount microelectronic components, an approximation of printed circuit board (PCB) model analysis can be made by assuming PCB as a bare unpopulated thin plate because the increase in stiffness of PCB due to the mounting of the components is approximately offset by the increase in total mass of the populated PCB [2]. However, this approximation can lead to errors in natural frequency prediction for different package profiles, for flip-chip-on-board (FCOB) and plastic-ball-grid-array (PBGA) assemblies [3,4]. When the component has small profile, the approximation of PCB assembly as a bare PCB can provide satisfactory modal analysis results because the stiffness and mass contribution of small component to PCB assembly is not significant. In this study, varying G-level random vibration tests for PCB assembly were conducted. In order to assess the reliability of PCB assembly, it is necessary to conduct the dynamic analysis. A global-local modeling approach [4-6] was used. The analyses by Basaran [7,8], Chandaroy [9] and Zhao et al. [10] show that solder joint deformation is in the elastic range for vibration loading. The global-local or submodeling method [11-13] has been used for the board level FE simulation. In this study, four different model cases were investigated for FEA modal analysis to calculate the first order natural frequency of the FCOB assembly. A quasi-static analysis approach was conducted for the FCOB assembly to evaluate the stress strain behavior of the solder joints. A harmonic analysis was also investigated to study the dynamic response of the FCOB assembly subjected to vibration load. Fatigue life prediction results from the quasi-static analysis and harmonic analysis approaches were compared to the test results. 1.3 PROJECT PURPOSE In this modern world due to the causes of health and environmental issues the electronic manufacturing industries facing a challenging problem of necessity to produce reliable solder products in very high density with very low cost. Solder joints are very important to the reliability of Printed Circuit Boards (PCB). This is a one of the leading factor in transmission of electrical and thermal connections. In case of every PCB even a smaller solder joints are very important. So this project investigates the Effect of Vibration on Solder Joint Reliability in Electronics Assembly Applications. Solder joint of a Electronic assembly is very important measurement because of This model based study might help engineers effectively improve the PCB mechanical design and thus improve reliability of electronics attached to the PCB by considering realistic uncertainties and adverse vibration environments. CHAPTER 02 LITERATURE REVIEW 2.1 SINE ON RANDOM VIBRATION TESTING Vibration sine on random testing is performed by superimposing a sine wave on top of a random environment. A sine on random vibration test duplicates the combined environment of a spinning helicopter blade with its distinct resonant levels and the rest of the aircraft which generates random engine and aerodynamic induced vibration. Gunfire on board an aircraft causes sine vibration while the rest of the aircraft generates random excitations. These types of tests are duplicating vibration characterized by dominant peaks (sinusoids) superimposed on a broadband background Another variation would be a swept sine on random test. 2.2 SINUSOIDAL VIBRATION TESTING Dynamic deflections of materials caused by vibration can cause a host of problems and malfunctions including failed electrical components, deformed seals, optical and mechanical misalignment, cracked or broken structures, excessive electrical noise, electrical shorts, chafed wiring. Because sine vibration is basically a certain fundamental frequency and the harmonics of that fundamental, in its pure state, this type of vibration is generated by a limited but significant number of sources. Expressed as amplitude versus frequency, sine vibration is the type of vibration generated in the field by sources such as engine rotational speeds, propeller and turbine blade passage frequencies, rotor blade passage and launch vehicles. While much of real world vibration is random, sine vibration testing accomplishes several important goals in product qualification and testing. Much material and finished product was modeled on some type of sine vibe signature. A sine sweep of frequencies will determine whether the assumptions were correct and if the deviations are significant enough to cause design changes. In other words, sweep will establish if the anticipated frequency has been met and/or discovers the test item fundamental frequency. Similarly, a sweep will help identify the test subject resonance frequencies, which may be the points at which the item experiences particularly stressful deflections. By dwelling at those frequencies in subsequent tests, premature failures due to the properties of the material may come to light before the items sees field use. Some of the following tests include fixed frequency at higher levels of the controlling variable (displacement, velocity, acceleration), and random vibration . Per customer request, NTS will run sweeps in one direction, decreasing, increasing or bi-directionally and can change frequency logarithmically or linearly. Another typical sinusoidal vibration test, sine burst such as the teardrop, goes rapidly to peak pulse and then decays at lower rate (to prevent damage to the unit). The burst test puts a maximum load into an article at a rapid rate and particularly stresses joints and seams to identify workmanship and design issues. 2.3RANDOM VIBRATION TESTING The legitimacy of random vibration s an effective tool of screening work man ship defects came about during manufacturing. Up until that limited hertz sine was applied during reliability testing. Pure sinusoidal vibration is composed of a single frequency at any given time. Comparisons tests revealed that to equal the effectiveness of random vibration. The test item will have to be subjected to many sine frequencies over a longer period of time, and may unintentionally fatigue the test item. Random vibrations undercover defect faster. 2.4 Real world simulation. Most vibration in real world is random for example a vehicle travelling over road experience random vibration from the road irregularities. A ground launched rocket vehicle experiences non stationary vibration during its flight the motor ignites the rocket travel through the atmosphere , the motor burn ends and so forth even in wing when subjected to turbulent air flow, undergoes random vibration. Random vibration is composed of multitude of continues spectrum of frequencies. Motion varies randomly with time. It can be presented in the domain by a power spectral density function [G2/Hz]. HIGHLY-ACCELERATED LIFE TESTING (HALT) Exposes the product to a step-by-step cycling in environmental variables such as temperature, shock and vibration. HALT involves vibration testing in all three axes using a random mode of frequencies. Finally, HALT testing can include the simultaneous cycling of multiple environmental variables, for example, temperature cycling plus vibration testing. This multi-variable testing approach provides a closer approximation of real-world operating environments. Unlike conventional testing, the goal of HALT testing is to break the product. When the product fails, the weakest link is identified, so engineers know exactly what needs to be done to improve product quality. After a product has failed, the weak component(s) are upgraded or reinforced. The revised product is then subjected to another round of HALT testing, with the range of temperature, vibration, or shock further increased, so the product fails again. This identifies the next weakest link. By going through several iterations like this, the product can be made quite robust. With this informed approach, only the weak spots are identified for improvement. This type of testing provides so much information about the construction and performance of a product, that it can bequite helpful for newer engineers assigned to a product with which they are not completely familiar. HALT testing must be performed during the design phase of a product to make sure the basic design is reliable. But it is important to note that the units being tested are likely to be hand-made engineering prototypes. At Trace, we have found that HALT testing should also be performed on actual production units, to ensure that the transition from engineering design to production design has not resulted in a loss of product quality or robustness. Some engineers may consider this approach as scientifically reasonable, but financially unrealistic. However, the cost of HALT testing is much less than the cost of field failures HIGHLY-ACCELERATED STRESS SCREENING (HASS) HASS testing is an on-going screening test, performed on regular production units. Here, the idea is not to damage the product, but rather to verify that actual production units continue to operate properly when subjected to the cycling of environmental variables used during the HASS test. The limits used in HASS testing are based on a skilled interpretation of the HALT testing parameters. The importance of HASS testing can be appreciated when one considers todays typical manufacturing scenario. Circuit boards are purchased from a vendor who uses materials purchased from other vendors. Components and sub-assemblies are obtained from manufacturers all over the world. Often, the final assembly of the product is performed by a subcontractor. This means that the quality of the final product is a function of the quality (or lack thereof) of all the components, materials, and processes which are a part of that final product. These components, materials, and processes can and do change over time, thereby affecting the quality and reliability of the final product. The best way to ensure that production units continue to meet reliability objectives is through HASS testing. RELIABILITY Reliability is defined as the probability that a device will perform its required function under stated conditions for a specific period of time. Predicting with some degree of Confidence is very dependent on correctly defining a number of parameters. For instance, choosing the distribution that matches the data is of primary importance. If a correct distribution is not chosen, the results will not be reliable. The confidence, which depends on the sample size, must be adequate to make correct decisions. Individual component failure rates must be based on a large enough population and relevant to truly reflect present day normal usages. There are empirical considerations, such as determining the slope of the failure rate and calculating the activation energy, as well as environmental factors, such as temperature, humidity, and vibration. Lastly, there are electrical stressors such as voltage and current. Reliability engineering can be somewhat abstract in that it involves much statist ics; yet it is engineering in its most practical form. Will the design perform its intended mission? Product reliability is seen as a testament to the robustness of the design as well as the integrity of the quality and manufacturing commitments of an organization. One of the fundamentals of understanding a products reliability requires an understanding of the calculation of the failure rate. The traditional method of determining a products failure rate is through the use of accelerated vibration operating life tests performed on a sample of devices. The failure rate obtained on the life test sample is then extrapolated to end-use conditions by means of predetermined statistical models to give an estimate of the failure rate in the field application. Although there are many other stress methods employed by electronic assembly manufacturers to fully characterize a products reliability, the data generated from operating life test sampling is the principal method used by the industry for estimating the failure rate of a electronic assembly in field service. Failure Rate (ÃŽÂ ») Measure of failure per unit of time. The useful life failure rate is based on the exponential life distribution. The failure rate typically decreases slightly over early life, then stabilizes until wear-out which shows an increasing failure rate. This should occur beyond useful life. Failure In Time (FIT) Measure of failure rate in 109 device hours; e. g. 1 FIT = 1 failure in 109 device hours. Total Device Hours (TDH) The summation of the number of units in operation multiplied by the time of operation. Mean Time between failures (MTBF) Reliability is quantified as MTBF (Mean Time Between Failures) for repairable product and MTTF (Mean Time To Failure) for non-repairable product. A correct understanding of MTBF is important. A power supply with an MTBF of 40,000 hours does not mean that the power supply should last for an average of 40,000 hours. According to the theory behind the statistics of confidence intervals, the statistical average becomes the true average as the number of samples increase. An MTBF of 40,000 hours, or 1 year for 1 module, becomes 40,000/2 for two modules and 40,000/4 for four modules. Sometimes failure rates are measured in percent failed per million hours of operation instead of MTBF. The FIT is equivalent to one failure per billion device hours, which is equivalent to a MTBF of 1,000,000,000 hours. The formula for calculating the MTBF is ÃŽÂ ¸ = T/R. ÃŽÂ ¸ = MTBF T = total time R = number of failures MTTF is stands for Mean Time To Failure. To distinguish between the two, the concept of suspensions must first be understood. In reliability calculations, a suspension occurs when a destructive test or observation has been completed without observing a failure. MTBF calculations do not consider suspensions whereas MTTF does. MTTF is the number of total hours of service of all devices divided by the number of devices. It is only when all the parts fail with the same failure mode that MTBF converges to MTTF. ÃŽÂ ³= T/N ÃŽÂ ³ = MTTF T = total time N = Number of units under test. If the MTBF is known, one can calculate the failure rate as the inverse of the MTBF. The formula for (ÃŽÂ ») is: where r is the number of failures. Once a MTBF is calculated, probability can derive from following equation: R(t) = e-t/MTBF Confidence Level or Limit (CL) Probability level at which population failure rate estimates are derived from sample life test. The upper confidence level interval is used. Acceleration Factor (AF) A constant derived from experimental data which relates the times to failure at two different stresses. The AF allows extrapolation of failure rates from accelerated test conditions to use conditions. Since reliability data can be accumulated from a number of different life tests with several different failure mechanisms, a comprehensive failure rate is desired. The failure rate calculation can be complicated if there are more than one failure mechanisms in a life test, since the failure mechanisms are thermally activated at different rates. Equation 1 accounts for these conditions and includes a statistical factor to obtain the confidence level for the resulting failure rate. THE BATHTUB CURVE The life of a population of units can be divided into three distinct periods. Figure 1 shows the reliability bathtub curve which models the cradle to grave instantaneous failure rates vs. time. If we follow the slope from the start to where it begins to flatten out this can be considered the first period. The first period is characterized by a decreasing failure rate. It is what occurs during the early life of a population of units. The weaker units die off leaving a population that is more rigorous. This first period is also called infant mortality period. The next period is the flat portion of the graph. It is called the normal life. Failures occur more in a random sequence during this time. It is difficult to predict which failure mode will manifest, but the rate of failures is predictable. Notice the constant slope. The third period begins at the point where the slope begins to increase and extends to the end of the graph. This is what happens when units become old and begin to fail at an increasing rate. Reliability Predictions Methods A lot of time has been spent on developing procedures for estimating reliability of electronic equipment. There are generally two categories: (1) predictions based on individual failure rates, and (2) demonstrated reliability based on operation of equipment over time. Prediction methods are based on component data from a variety of sources: failure analysis, life test data, and device physics. For some calculations (e.g. military application) MIL-HDBK-217 is used, which is considered to be the standard reliability prediction method. A simple failure rate calculation based on a single life test would follow equation 1. ÃŽÂ »Ã¢â€š ¬Ã‚  = failure rate. TDH = Total Device Hours = Number of units x hours under stress. AF = Acceleration factor, see Equation 3. Since reliability data can be accumulated from a number of different life tests with several different failure mechanisms, a comprehensive failure rate is desired. The failure rate calculation can be complicated if there are more than one failure mechanisms in a life test, since the failure mechanisms are thermally activated at different rates. Equation 1 accounts for these conditions and includes a statistical factor to obtain the confidence level for the resulting failure rate where, ÃŽÂ » = failure rate in FITs (Number fails in 109 device hours) ÃŽÂ ² = Number of distinct possible failure mechanisms k = Number of life tests being combined xi = Number of failures for a given failure mechanism i = 1, 2, ÃŽÂ ² TDHj = Total device hours of test time for life test j, j = 1, 2, k AFij = Acceleration factor for appropriate failure mechanism, i = 1, 2, k M = ÃŽ2 (ÃŽÂ ±, 2r +2) / 2 where, ÃŽ2 = chi square factor for 2r + 2 degrees of freedom r = total number of failures (ÃŽÂ £ xi) ÃŽÂ ± = risk associated with CL between 0 and 1. 2.2 SOLDER PASTE 2.1.1 ROLE OF SOLDER PASTE IN REFLOWING Solder paste is a combination mixture of a flux composition and a highly grinded, powdered solder metal alloy that is normally used in the electronics industry to soldering processes. And also it is call as a attachment medium between the device interconnection features and the PCB itself. The components of a solder paste are specially designed for excellent printing and reflow characteristics. In normal case of the surface mount soldering process involves placing the substrate and a small amount of solder paste in a printed circuit board. After that the system will be heated until the solder reflows, forms an electrical connection between the solder pad and the electrical contact of electronics part. After this reflow finished it forms both an electrical and mechanical connection between the electronics components and the printed circuit board. 2.1.2 SELECTION CRITERIA OF A SOLDER PASTE Selection of a solder paste is very important factor for reflowing process, reliability its quality. The following factors are considerable for a good solder paste [6]. The size of the solder alloy particles which are in the solder paste The tendency to form voids The properties of the flux medium of the solder paste Alpha particle emission rate The design of the stencil to be used for printing Thermal properties of the solder paste Electrical properties of the solder paste CHAPTER 03 EXPERIMENTS 3.1 MATERIALS AND METHODOLGY SOLDER PASTE Basically I used solder paste in same procedure. The details of solder paste used in the experiment are given in the following table TYPE OF SOLDER PASTE ALLOYS CODING PARTICLE SIZE METAL LOADIND S1 Sn95.5Ag4Cu0.5 S2 Sn42Bi57Ag1 Table 3.1.1 types of solder paste used in experiment For this project all above solder paste should be in a container with appropriate labelling and identification on it to distinguish it from the Tin lead solder paste. The solder paste should be stored in a refrigerator between 35 45 F. and should be allowed to come room temperature for minimum four hours before doing the solder paste printing. Once it has finished the using solder paste must replace to the refrigerator since it can not be at room temperature over 24 hours. The self life of the lead free solder pastes may be reducing from the typical six month. The above guidelines are strictly followed in this project. Because it is not only for guarantee the quality of solder paste but also a good way to reduce the errors that may affect the final results of the project. SOLDER PASTE PRINTING IMPORTANT OF SOLDER PASTE PRINTING Surface mount technology (SMT) is used extensively in the electronics industry. Surface mount components are potentially more reliable products can be designed and manufactured using the SMT. The solder paste stencil printing process is very critical and important step in the surface mount manufacting process. Most of all the soldering defects are due to problems dealing with the screening process. So we want to a major consideration in operation and set up steps in stencil printing process. When we are monitoring these factors carefully we can minimize the defects. The main purpose of printing solder paste on PCB is to supply solder alloy to solder joint to correct amount. That only print must be aligned correctly and can get a perfect component placement. PRINTING PROCESS PARAMETERS Some of the following parameters are very important to printing process. STENCIL Stencils are using for the solder paste slip easily off the aperture edges and thereby secures a uniform print. For this process we using electro formed stencils. Because of these stencils have very shape edge and slightly conic. Generally a stencil is mading from cupper or nickel [12]. ENVIRONMENTAL Dust and dirt from the air that will reach the PCBs and stencils can be defects poor wet ability in the reflow soldering process. So PCBs should be stored in sealed packages and cleaned before use. SOLDER PASTE Solder paste characterise must be controlled to achieve a maximum production results. Some of the factors are given below [12]. Percent of metal Viscosity Slump Solder balls Flux activity working life and shelf life STENCIL PRINTING PARAMETERS Stencil printing parameters are very important factors in printing processes to achieve a best yield. The following parameters must be monitors and controlled in a printing process. Squeegee pressure = 8kg Squeegee speed = 20 mm/s Separation speed = 100% Printing gap = 0.0 mm These factors and limit can be adjust for our project purpose SOLDER PASTE PRINTING EQUIPMENT AND PROCESS Figure 3.2.4.1 DEK 260 stencil printing machine The DEK 260 stencil printing machine is used to print solder paste on the circuit board. This DEK 260 stencil printing machine has two main functions. Registers the position of the product screen with in the print head Positioning the circuit board below the stencil, to ready for the print cycle. The boards to be print are supported on magnetic tooling and held by vacuum caps arranged on the plate to guarantee the board steady during the printing on to the board. The first step of the experiment is to do the solder paste printing on to the board. In this project unable to get metal stencil, so circuit boards are printed by hand, below procedure followed to print PCB Put weights onto the stencil to fix it roll the squeegee over the stencil solder paste presses through the aperture onto PCB separate stencil two circuit boards are printed with solder paste for each solder paste types. Totally 4 circuit boards printed. SOLDER PASTE REFLOWPROCESS/PROFILE Figure 3.3.1 reflow oven To achieve a good reliable solder joint the reflow process is very important. When doing the reflow with sn-pb solder paste often performed at minimum peak temperature of about 203. It is 20k above the sn pb liquid state temperature. When doing the reflow process with lead free solder paste it has to be performed at a minimum peak temperature of 230. It is just 13K above the melting temperature. It is generally accepted that lead free solders requires a higher reflow temperature up to 220 230. Reflow profile will be affecting the reliability of a solder joint. Because it is a major factor that influence the formation of the intermettallic layers in a solder joint. Intermettalic layer is a critical part of a solder joint. An intermettalic bond thickness should be thin. Therefore a good reflow profile must produce solder bumps with a thin intermetallic layer. PREHEAT ZONE In this zone indicates how the temperature is changing fast on the printed circuit board. The ramp-up rate is usually between 1-3 per second. If this rate exceeds there will be damage to components from thermal shock. Only In this preheat zone the solder paste begins to evaporate. So if the rise rate is too low the evaporation of flux is not incomplete. This will affect the quality of the solder joint. THERMAL SOAK ZONE It is also called the flux activation zone. In this thermal soak zone it will take 60-120 seconds for removal of solder paste and activation of fluxes. Solder spattering and balling will be happen if the temperature is too high or too low. End of this thermal shock zone a thermal equilibrium will complete the entire circuit board. REFLOW ZONE In this reflow zone only the maximum temperature will be reached. In this zone we have to consider about the peak temperature that is the maximum allowable temperature of entire process. It is very important to monitor this maximum temperature exceeds the peak temperature in this zone. It may cause damage to the internal dies of SMT components and a block to the growth of intermetalic bonds. we have to consider the profile time also. If time exceeds than the manufactures specification it also affect the circuit boards quality. 3.3.4 COOLING ZONE In the reflow process the last zone is cooling zone. A proper cooling inhabits excess intermetallic formation or thermal shock to the components. Generally the cooling zone temperature range is 30 100. In this project I selected the following temperature profiles. This temperature profile is stranded reflow profile for lead free soldering. Zone 1 220 Zone 2 180 Zone 3 170 Zone 4 190 Zone5 233 Zone 6 233 Totally 4 circuit boards were printed. Choosing of good reflow profile was not involves any defects or damages in the printed circuit board. Figure 3.3.4.1a printed circuit board after reflow SET UP EVENT DETECTOR The constructed PCBs were connected with event detector by ribbon data cable. Ribbon cable addressed according to `Analysis tech STD series event detectors manual . pins 1 to 32 function as source point and pins 33 to 37 function as ground point. To obtain closed loop circuit to monitor the behaviour of PCB components, PCB boards 1, 2, 3 and 4 connected to channel 1,2,33 and 34 respectively. Ribbon cable After connected ribbon cable with event detector and enviromenrt chamber, channels are assigned in WIN DATA LOG software which supplied with event detector. For this test following settings define for data acquisition INVESTICATING RELIABILITY OF SOLDER JOINT UNDER VIBRATION CHAMER In this study, PCBs were used in Variable Frequency Vibration Test to analyse the dynamic response of PCB assembly subjected to random vibration loading. The PCB specimens were tested at different acceleration levels to assess the solder joint reliability subjected varying G-level vibration loads(G is the gravitational acceleration), respectively. Vibration tests were accomplished by using an electro dynamic Shaker

Harriet Beecher Stowe :: essays research papers

  Ã‚  Ã‚  Ã‚  Ã‚  Harriet Beecher Stowe, the author of Uncle Tom’s Cabin, was born in Litchfield, Connecticut in the year of 1811. She was a housewife of six, and wrote articles for magazines for a living. Stowe’s sister, Isabella Jones Beecher, was furious from the passing of the Fugitive Slave Law, passed as part of the Compromise of 1850. The law required all Northerners to return runaway slaves to their Southern owners. The result of the anger of the two sisters resulted in the production of Uncle Tom’s Cabin. When reading the book, it is quite obvious to an observant reader that the book was written by a nineteenth century woman during the nineteenth century. The opening scene of the book, where Mr. Shelby talks to Haley about Tom, is a reference to Harriet Beecher herself. She is trying to portray that all themes in this book about the evils of slavery are unfortunately true. There were some bright points besides the evils of slavery. Stowe mentioned that slavery in Kentucky was not so badly-off. This, however, angered abolitionists. Even though, there were still many fears to worry about. Another point is that Stowe makes Eliza and George, the parents of little Harry, light skinned. Stowe remarks that light-skinned women, like Eliza, are often especially attractive. This is one stereotype that whites have over blacks. The stereotype is described fully in the description of the two light-skinned story characters.   Ã‚  Ã‚  Ã‚  Ã‚   All of the characters in Uncle Tom’s Cabin are based on real acquaintances of Harriet Beecher Stowe. Eliza is based on a young woman that Stowe had met in Kentucky. The first indication of this is found in Chapter 3: The Husband and the Father. In this chapter, George Harris decides to run away to Canada and work to buy Eliza and Harry’s freedom. Also in this chapter, George and Eliza possess completely different thoughts about slavery.   Ã‚  Ã‚  Ã‚  Ã‚  All in all, most of the situations and characters in this book are references to Harriet Beecher Stowe and the life she lived.

What Did You Buy Into Today? Essay -- Advertising Media Papers

What Did You Buy Into Today? Take a look at your shoes. Check the breast of the shirt you are wearing. Don’t forget the ass of your pants. What about the food you ate for lunch or the computer you typed your paper on? There is no denying that we are living in a brand name life. People have become consumers whether they’ve wanted to or not. It is impossible to walk through life without being bombarded by image after image of a branded identity. From Nike to McDonald’s, Apple to Evian, the â€Å"brand† has worked its way into consumer consciousness on a level that has not been seen in the past. Humans strive for individuality, so how did we so willingly give ourselves over to the brands that now consume us? A common misconception about branding is that branding and advertising are both one in the same. This, however, is not the case. Advertising is only one key component that a company uses to create their own branded image; an image that encompasses everything the company wants the public to know about the meaning of its products. Advertising is just an outlet to get that message across. â€Å"Branding† is a by-product of a society that has too many similar products, a natural occurrence in a free-market capitalist country. The goal of branding is to separate one similar product from another by altering the way that a consumer feels about a certain product at a sub-conscious level. For instance, a marketing campaign common to almost all of us tries to create a distinction in our mind between Coke and Pepsi. To do this, brand makers will work to infiltrate their target market and create an image for the product that closely resembles the image of the target market, thus burning i n the idea that their product is an important aspect of so... ...Nike swoosh being altered to resemble a gun shooting the high soaring basketball player. The results are quick and effective, and spread to others outside your immediate sphere of influence. The more you expose the underlying meaning of the ads around us the more people will think about all the ads and marketing pushes that coincide with their life. It’s time to once again reclaim your life as your own. Question the images put before you. Urge others to do the same. Support independent retail outlets and companies that still produce the products that they are selling to you. If you must buy branded products, purchase them second hand. If there’s a mass exodus away from the cash registers of these branded pseudo companies then the tides will change and we’ll see our lives return to us as they once stood, uninterrupted and full with a passion for living once again.