Project Management and How it Relates to Purchasing and Supply Research Paper

Project Management and How it Relates to Purchasing and Supply Management - Research Paper Example In this scenario, project management processes are required to perform these operations successfully. The basic purpose of this research is to analyze project management in the context of its use in procurement and supply management. Procurement and Project Management Procurement is the most important element of a business industry. It encompasses a wide variety of aspects of project management such as acquiring material, goods, equipment, and services from external firms. However, procurement does not include other internal departments inside an organization. In view of the fact that procurement is a domain for which a project manager will be responsible for providing information and input, in various and possibly a number of firms, hence it is believed to be an area that the project manager does not own. Though, the project managers generally are not authorized to take part into contracts in support of the business organization, as well as they are not responsible for controlling t he contracts once they are prepared or in process. However, it is still a most important area which an organization must need to have knowledge of. In this scenario, the project Management Institute (PMI)’s Project Management Body of Knowledge (PMBOKÂ ®) outlines six key processes that deal with certain Project Procurement Management knowledge areas (Mochal, 2007). Plan purchases and acquisitions: This process of project management is concerned with identifying and determining the resources that need to be acquired for a project and when a project needs them. This area of procurement comes directly under the control and authority of the project manager, for the reason that the top management and organization’s purchasing committee do not... This paper has presented a detailed analysis of the project management function in the context of its role in procurement and supply chain management. Project management is a set of well-organized and synchronized processes, and each process is connected with another however the basic purpose remains to achieve a common goal. The research has shown that both the project management and supply chain management are similar disciplines. The research has also shown that if both supply chain management and project management are combined effectively then it can improve the performance and efficiency of a firm. This paper has also discussed various aspects associated with procurement and purchasing. This paper has also presented recommendations on how to use project management to improve procurement and supply chain processes. In short, the survival of successful project management depends seriously on the proper execution of the supply chain process, for the reason that well-timed, accurat e, and well-organized delivery of materials, equipment, supplies and resources are critical to success of project management. In order to make the procurement process a success, there is a need for reliable aftercare and organizational record, which should be carried out by a variety of professionals from the legal and financial settlement of purchases. In addition, even a project is in progress, the performance of the suppliers should be constantly assessed and, where essential, alternatives should be adopted.

The presence of the current financial crises has made investors more Essay

The presence of the current financial crises has made investors more determined in handling excess remunerations - Essay Example Introduction A vote against remuneration is significant if it receives less than 75 percent of the shareholders support. Thus, votes have been on the use recently in protesting against pay increases that are insufficiently linked to performance. For instance, Section D of the U.K corporate governance code sets out remuneration guidelines for both the executive and non-executive directors. According Tricker (2012) section D.1, â€Å"the remuneration should be sufficient enough to motivate and attract directors, but a company should avoid paying more than is necessary for this purpose. A significant proportion of the executive director’s remuneration should be structured so as to link rewards to corporate and individual performance.† Section D.1.4 of the U.K corporate governance states that it is the responsibility of the remuneration committee to consider compensation commitments of their directors in the event of early termination. MM & K report is recent and its releas e fueled investor’s activism in fighting against pay rise. The report revealed that the medium total pay rise for FTSE 100 CEOs is 10 percent and one quarter of the CEOs in this index had 41 percent increment on their pay. Research indicates that the size of pay that a FTSE director has increased unexpectedly. For instance, between years 1990 and 2000, the remuneration of a FTSE chief executive went up by 13.6 percent annually from ?1 million to ?4.2 million. In year 2011, FTSE remuneration rose by 11 percent. The current average pay rise in the market is 1.7 percent. In 2012, there have been 24 similar incidents in total all over Europe compared to 2011 which had 25 cases. The legislation has been carefully following these protests, and the pending U.K legislation shows that by year 2012, pay plans will have to pass the majority vote or shareholders will have the authority to reject management’s remuneration proposal. New disclosure rules are also in the process of co ntemplated purposely to help the shareholders in making a decision. For example, in France the new socialist government is contemplating to impose pay limits on executives in companies which own a majority stake. The pay will be 20 times that of the lowest paid employee in the company thus leading to substantial pay cuts. Also, the contemplated Legislations will exert pressure on companies where the government owns share but not a controlling share. CEO’s of companies such as AstraZeneca, Aviva, trinity Mirror is some of directors who had been forced to resign over pay and performance related problems even before news broke. WPP Group During the 2012 annual general meeting, approximately 59 percent of the WPP investors voted against the company’s remuneration report and the CEOs pay package of ?6.8 million. In the previous year, over 40 percent of the shareholders had a ‘no’ vote on pay and this prompted the remuneration committee to reach out the sharehol der before the 2012 AGM. After the shareholders vote the chairman of the group said, â€Å"

Oedipus the King- Critical Analysis Essay Example | Topics and Well Written Essays - 1500 words

Oedipus the King- Critical Analysis - Essay Example However, in the end we find out that this prophecy came true despite Oedipus’ attempt to steer clear of those results. In Oedipus the King, Sophocles makes it clear fate, choices, and one’s personality all go hand in hand. Before making an in-depth analysis of the story with respect to the thesis stated above, it is customary to make a quick go through the story. Laius, the King of Thebes is warned by Delphic oracle not to marry Jocasta because if he does, the couple would give birth to a baby who would kill Laius and marry Jocasta. Being ignorant towards the advice of the oracle, Laius marries Jocasta. Upon the birth of the child, Oedipus, Laius pierces the child’s ankle and leaves him unattended on a hill to die. A shepherd takes the child and delivers him to King Polybos in Corinth. The Delphic oracle finds Oedipus and tells him that he is destined to assassinate his father and sleep with his mother. Having heard such a dreadful decision of the destiny, Oedipu s resolves to run away from his family so that he would be able to make sure that he never commits the sin. On his way to Thebes, he encounters a stranger at a junction of three roads who happens to be Oedipus’s real father, Laius. Oedipus kills Laius, who is a stranger to him and proceeds to Thebes. As he reaches Thebes, he defeats the Sphinx and is rewarded with the position of the King of Thebes. He marries Jocasta in this position as she happens to be the queen. Jocasta somehow comes to know that Laius has been killed by a group of robbers. After a span of sixteen years or more, Thebes catches plague. As per his commitment with the public, Oedipus searches for the killer of Laius and ultimately gets to know that he himself is the person he has been looking for. Having realized the truth, Jocasta hangs herself to death and Oedipus loses his eye sight. The Chorus mourns the sorrowful destiny of King Oedipus. One of the most fundamental themes of this play is fate and the fa ct that it is beyond human power to escape fate. What is destined to happen, will happen at any cost and there is no way escaping it. This is what has happened with two main characters in the story, i.e. Laius and King Oedipus. By not paying heed to the divine warning made by oracle Delphic against his decision of marrying Jocasta, Laius essentially committed two sins; First, he went against the will of god and married Jocasta. Secondly, the act of leaving the newborn baby to hillside to no one’s discretion put Laius into guilt for the rest of his life. Laius resolved to leave the child alive on the hillside so that there would be at least one per cent chance of his survival (Vellacott 139). To this end, all that happened with Laius seems quite justified and reasonable since he had originally gone against the will of god. What is more important and yet, more difficult to comprehend is the reason for which Oedipus had to go through all the shameful experiences and reach the tr agic destination of blindness. Obviously, this had to happen since the oracle had warned Laius regarding the association of the very future with his act of marrying Jocasta at the outset. So Oedipus had to be the very son of Laius who was destined to be murderer and adulterer. But it seems just too unjust for Oedipus to be the victim of Laius’s mistake since he was innocent in whatever he did because that was done unintentionally and not knowingly. However, the author does seem to make sense for punishing

ANNOTATED BIBLIOGRAPHY Essay Example | Topics and Well Written Essays - 1000 words

ANNOTATED BIBLIOGRAPHY - Essay Example The use of social media, specifically Twitter has encouraged EFL/ESL learners to openly express themselves in their acquired language without fear of reprimand or ridicule from those around them, or their teachers (Junco, 2011). Students are more at home in this virtual environment and find themselves openly using the written English language to express themselves in an atmosphere where they can double check their grammar and spelling before sending out any message. The ability to ensure that communication is fluent as well as making sure that that the social posts are conveying some important messages makes Twitter an effective teaching tool for written English. The aim of this of this paper is to review current findings regarding the possible benefits of using Twitter as a written English teaching tool. The technology allows for a greater vocabulary acquisition among students through the effective use of Twitter in the practice of their written English skills (Junco, 2011). In this paper, a detailed review of the six articles is done. The articles define the reasons as to why Twitter makes for an effective teaching tool for written English with respect to EFL and ESL learners. Borau, K, et al. (2009). Micro-blogging for language learning: using twitter to train communicative and cultural competence. Advances in web-based learning - icwl. Berlin/New York: Springer Berlin Heidelberg Borau's article begins with an introduction to the fact that most English learners use Twitter as an active way of learning rather than a passive version. The author goes on to explain that students taught using various types of technologies have shown a remarkable improvement in their grasp and usage of the English language due to their ability to constantly practice the written version of the language online via Twitter. The specific mention of Twitter in the study was done in relation to a specific study done at the Shanghai Jiao Tong Distance College where ESL students were taug ht via online correspondence for a whole summer term in 2007. The article is very interesting as far as Twitter effect on written English is concerned. It is easy to agree with the article because the results of the experiment were quite successful and pointed towards the ability of Twitter to allow students to learn how to express themselves in effectively in English using only 140 characters. Cano, E. (n.d.). Mobile learning with twitter to improve linguistic competence at secondary schools. The New Educational Review, 134 -147. This article entails a study that was done within three school districts in Spain. In each school district, Twitter was used as part of the interdisciplinary program to develop linguistic competence among learners. Twitter was used as the main communication tool in this instance and it proved to be highly promising as a teaching tool for written English. In the article, Cano concluded that Twitter managed to promote a substantial improvement in terms of te aching and learning for both teachers and students respectively. This happened especially when the language is studied from a reading and writing perspective. It is agreeable with the author in the sense that he made mention of the ready availability of Twitter through various mediums such as tablets, laptops, and mobile phones which encourage students to practice their ESL writing skills during

The Work of Discipleship Research Paper Example | Topics and Well Written Essays - 1750 words

The Work of Discipleship - Research Paper Example Majorly, Christology bases on the Apostolic Age of the gospel that is during the days of the apostle Paul. The themes and ideas of Paul were built on the worship of Christ as Lord and Christ’s pre-existence, forming the epicenter of Christology. There have been arguments to the fact that there are several Christophany cases in the Old Testament and that the numerous biblical records account for the preexistence of Jesus Christ. In this aspect, the term Christophany is a term that is considered to be more appropriate as compared to the term Theophany because of the belief that God’s visible manifestations represent the pre-incarnation of Christ. 1There have been arguments pointing to the fact that the Old Testament’s records of the appearing of the Lord’s Angel were Christ’s pre-incarnate. The Angel of the Lord is understood by many to be a theophany that is true. Over the years, especially after the Apostolic Age, the early church was thrown into debates that often got politicized and fierce concerning issues that are interrelated in Christianity. Among the issues that were being debated was Christology, with the matter finding its way to the ecumenical councils as a contentious issue. These coun cils were dubbed as the Christological councils that base their focus on the teachings of the condemnation of interpretations that were incorrect regarding Jesus Christ’s life and works. St. Thomas Aquinas was the first to provide a systematic Christology in the 13th century. His view was instrumental in the resolution of a good number of issues that were there at that time. Aquinas in his Christology focused on the championing of the view of the perfection of the human attributes of Christ. Through the middle ages, there was the witnessing of the emergence of a different view of Christ as being a source of comfort and love and true living friend in addition to being the Lord. 2Modern Christology, therefore, seeks to

Forgive Me Mother Essay Example for Free

Forgive Me Mother Essay Its strange how memories of the past can be so terrifying. The thoughts and the occurring dreams are always similar. I would remember longing for a summer where the summers light would beam on my body with the warmth of the sun. Winter was worse because I was terrified by the cold thick air that I would inhale inside my thin body until it feels I was shivering to death. The feeling of being alone , I couldn’t even sleep at night without being terrified; not because of being alone , but knowing my life would dwell with no hope for me for the future. I would see paranormal faces of my father. The haunting face would stare at me with such gentle eyes , yet sad. It’s like he was watching over me. Years ago when I had a family, loving yet annoyingly humorous in a family sense that I miss. We were having dinner with the family with just me , my mother and father. My mother was preparing the food and my father was coming home from work. However he never came back and my mother was worried and panicked. I was still too naà ¯ve to understand the situation fully back then. Hell I don’t even know how old I am anymore since I’ve lost track of time. I cried at first because my mother was always the strong type in the family. It was the first time I’ve seen her cry and the emotions inside of me wanted me to cry with her. He never came back and the authority’s told us he went missing. He was the provider of the family and we were financially unstable. My mother had to look for work , so she left to the city. She told me she would call me when she would be back. Once she left , the people who collects debt knocked on my door and seized the house. I had no place to go and so I left to find shelter and food. I got hired a job in a local newspaper agency to hand out flyers to neighbour streets. It was so cold but I never gave up hoping my mother would come back and take care of me. She couldn’t take me with her because she could only afford enough for herself to travel. We lived in a small town surrounded by snow somewhere in the upper regions of South Korea. One day while I was sleeping in the corner of the streets. A man walked pass with a white hat and apron with a grin on his cheeks. He looked at me for a couple of minutes. I was scared so I didn’t look back at him out of fear. I hear footsteps coming towards me and I was about to run. He asked â€Å"Why are you out in the streets alone at your age? , How old are you?†. I replied in a low voice ‘I don’t know†. He had a strange look on his face and asked me where my guardians was. I replied to him that I don’t know either. He asked me more questions which I all replied â€Å"I Don’t know†. I looked up and saw his face. He was a old man with a beard and had a stick on him which looked like it was supporting him move. It was a silent cold night and I’m not sure why he would be walking around at this time. He asked if I would like to work at his restaurant with cleaning and get paid for it. With nothing to lose I gladly accepted his offer. He took me to his place , it didn’t seem what he said it was. The restaurant looked like a dump and I only saw girls on the front door outside of the restaurant wearing what looked like beach clothing in cold weather. I was suspicious but I had nowhere to go and I didn’t know the way back from here. I followed the old man and he took me into a small room with 10 other children. At first I thought he was taking care of us until there was only girls in the room coming in and out one by one with a man. This isn’t a restaurant I suspected. I was disgusted and tried to leave but they didn’t let me leave. Pushing and crying to get out. They pulled me back , held both my hands and chucked me into a room by myself and locked the doors. Suddenly someone said *Calm down or they will punish you*. I stoped and looked for the source of the sound. The room had a little vent which leads to the other rooms. I whispered to the girl â€Å"What is this place† in a panicking voice. She told me it was a brothel where everyone gets kidnapped and rape for money by strangers. I asked her I was a male, â€Å"what do they want from me?† She told me she doesn’t know either. I didn’t want to find out , my life was already crumbling and now this. There was a medicine cabinet inside the room. I searched inside and found sleeping pills , I remember taking these when I lived with my parents. I could never sleep so the doctor prescribed me sleeping pills. I tried to sleep but I couldn’t out of the fear what was going to happen to me. I suggested to myself I should take these pills and ease things. I took the bottle of medicine from the cabinet. One wasn’t enough for me so I thought. I took more and more until I was feeling dizzy. I counted how many times and how much I’ve taken. But I lost count and started again. I needed more and I needed my peaceful slumber. I was scared to think what was going to happen and kept taking more and more pills until I could feel the bottom of the container. My body begins to weaken and I could no longer feel my fingers. My eyelids begin to shutdown. Soon darkness was all I could see , I felt a hollowing in a room with darkness and suspended in time. Forgive me mother I love you.

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