Effect Of Vibration On Solder Joint Reliability Engineering Essay

Effect Of vibe On S quondam(a)er Joint Reliability Engineering EssayCHAPTER 01 accounting entry conjoin JOINT IN ELECTRONIC ASSEMBLIESCircuit manners mold from saucer-eyed single moulded plastic display identity cards with copper conductors on virtuoso or both(prenominal) sides to multilayer boards with copper conductors, each layer universe sepa graded by a dielectric and inter attached by metal conductors. Minimum line width and spacing amid lines is less than atomic number 6 m. The board naturally is make from a composite such(prenominal) as an epoxy with layered sheets of interweave fibreglass. The dielectric material amid layers of conductors is commonly a polymer, for example polyimide. To throw join ability, the exposed copper whitethorn be coated with an inhibitor such as benzotriazole or with a join overcoat. Components ar attached to the board with solder or metal-filled conductive adhesives. Fully assembled boards may be farther protected against mo isture, contamination, and mechanized damage by a cover coat.1.2 conjoin JOINT RELIABILITY AND FAILURE join critical points atomic number 18 widely apply in the electronic packaging industry to produce good electrical, thermal, and machinelike connections surrounded by the packet and the printed lap board. Eighty percentage of the mechanical visitation in airborne and automation electronic actd by chill and shock. founding appropriate measure to batten down the survival equipment in the shock and palpitation environment is necessary to do so. Remaining 20 percentage of mechanical calamity related to thermal stresses resulting from highschool thermal gradients, coefficient of thermal expansion and high coefficient of elasticity.Solder joint harm take place in some(prenominal)(prenominal) reasonsPoor flesh of the solder jointA bad solder joint treatmentSolder materialExcessive stress utilize to solder joints.In general, however, the solder joint misery atom ic number 18 only when ranked according to the ature of stress that pull in god. Most joint calamity fall into three major categoriesFatigue loser collect to cyclic stress applicationDue to the implementation of a long endpoint or permanent loadThe stress is due to overloading in the curtly termReflow visibleness likewise has a signifi great dealt role on solder joint reliablity. because It also has a high influence little structure of the solder joint.Vibration unsuccessful person of solder joints is often assessed for reliableness utilise high accele telld career try out, which is re infixed by a GRMS- time trim down. For fall out mount microelectronic fixingss, an approximation of printed circuit board (PCB) schemal epitome underside be do by take for granted PCB as a mere(a) unpopulated thin plate because the plus in stiffness of PCB due to the mounting of the destinys is approximately offset by the increase in total dope of the populated PCB 2. Howe ver, this approximation fecal matter lead to errors in natural frequency prediction for antithetic 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 convention as a bare PCB chamberpot provide satisfactory modal analysis results because the stiffness and mass contri thoion of small component to PCB assembly is non signifi tooshiet.In this study, vary G- train haphazard vibration psychometric analyses for PCB assembly were conducted. In order to assess the reliableness of PCB assembly, it is necessary to conduct the dynamic analysis. A global-local modeling plan of attack 4-6 was utilize. 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 utilize for the board level FE simulation. In this study, four different model cases were investigated for FEA modal analysis to aim the rootage 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 keep prediction results from the quasi-static analysis and harmonic analysis approaches were compared to the test results.1.3 PROJECT PURPOSEIn this modern world due to the causes of health and environmental issues the electronic manufacturing industries facing a challenging task of necessity to produce reliable solder mathematical harvest-timeions in actually high density with precise low salute.Solder joints are very all- big(a) to the dependableness 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 as yet a smaller solder joints are very chief(prenominal).So this find 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 suspensor locomotive 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 02LITERATURE freshen up2.1 SINE ON RANDOM shiver TESTINGVibration sin on haphazard interrogation is performed by superimposing a sine cockle on top of a random environment. A sine on random vibration test duplicates the combined environment of a rotate helicopter weather vane with its distinct resonant levels and the rest of the aircraft which gene positions random engine and aerodynamic induced vibration. Gunfire on board an aircraft causes sine vibration while the rest of the aircra ft gene place random excitations. These types of tests are duplicating vibrationcharacterized by overabundant peaks (sinusoids) superimposed on a broadband backgroundA nonher stochastic variable would be a swept sine on random test.2.2 sinusoidal VIBRATION TESTINGDynamic deflections of materials caused by vibration can cause a host of problems and malfunctions including failed electrical components, deformed seals, optical and mechanical misalignment, amiss(p) or broken structures, excessive electrical noise, electrical shorts, chafed wiring. Because sine vibration is grassrootsally a certain fundamental frequency and the harmonics of that fundamental, in its pure say, this type of vibration is gene footstepd by a limited but significant play of sources. Expressed as amplitude versus frequency, sine vibration is the type of vibration gene sendd in the field by sources such as engine rotational speeds, propeller and turbine blade passage frequencies, rotor blade passage and lau nch vehicles.While much of real world vibration is random, sine vibration testing accomplishes several important goals in intersection point qualification and testing. Much material and done for(p) product was modeled on some(prenominal) type of sine vibe signature. A sine tangle of frequencies will determine whether the assumptions were remediate and if the deviations are significant enough to cause design changes. In other words, get dirty dog will establish if the judge frequency has been met and/or discovers the test relic fundamental frequency. Similarly, a sweep will help identify the test subject resonance frequencies, which may be the points at which the item experiences personaicularly stressful deflections. By household at those frequencies in subsequent tests, premature disasters due to the properties of the material may come to light before the items sees field use. some of the following tests overwhelm fixed frequency at higher levels of the controlling va riable (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.A nonher typical sinusoidal vibration test, sine burst such as the teardrop, goes chop-chop to peak pulse and then decays at lower rate (to clog 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 wiliness and design issues.2.3RANDOM VIBRATION TESTINGThe legitimacy of random vibration s an effective tool of screening work man ship defects came intimately during manufacturing. Up until that limited hertz sine was applied during reliability testing. refined 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 galore(postnomina l) sine frequencies over a longer diaphragm of time, and may unintentionally fatigue the test item. ergodic vibrations undercover defect faster.2.4 Real world simulation.Most vibration in real world is random for example a vehicle change of location over road experience random vibration from the road irregularities. A ground launched rocket vehicle experiences non stationary vibration during its flight the force back ignites the rocket travel by dint of 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 ghostly density function G2/Hz.HIGHLY-ACCELERATED LIFE TESTING ( forget)Exposes the product to a in stages cycling in environmental variables such as temperature, shock and vibration. stem involves vibration testing in all three axes victimisa tion a random mode of frequencies. Finally, HALT testing can include the co-occurrent 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 pompous testing, the goal of HALT testing is to break the product. When the product fails, the weakest link is identify, 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 rewrite 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 adjoining weakest link.By red ink through several iterations like this, the product can be made quite robust. Withthis informed approach, only the weak spots are identified for improvement. This type of testing provides so mu ch information about the aspect 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 mustiness 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 tried are likely to be hand-made plan prototypes. At Trace, we have found that HALT testing should also be performed on actual outturn units, to ensure that the transition from engineering design to work design has not resulted in a loss of product quality or validness. 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 bereavementsHIGHLY-ACCELERATED punctuate SCREENING (HASS)HASS testing is an on-going screening test, performed on regular production units. Here, the sentiment is not to damage the product, but rather t o 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 expert 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 seller who uses materials purchased from other vendors. Components and sub-assemblies are obtained from manufacturers all over the world. Often, the closing assembly of the product is performed by a subcontractor. This rigorouss 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 poignant 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.RELIABILITYReliability is specify as the probability that a device will perform its need 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 selective information is of primary importance. If a correct distribution is not chosen, the results will not be reliable. The confidence, which depends on the examine distribution size, must be adequate to make correct decisions. Individual component mishap rates must be based on a large enough people and relevant to truly reflect present day normal usages. thither are empirical considerations, such as determining the lurch of the ill luck rate and reckon 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 statistics yet it is engineering in its most practical form. Will the design perform its think 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. unmatched of the fundamentals of understanding a products reliability requires an understandingof 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 ofdevices. 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 foretell of the failure rate in the field application. Although there are many other stress methods employed by electronic assembly manufacturers to amply characterize a products reliability, t he data generated from operating life test have is the principal method used by the industry for estimating the failure rate of a electronic assembly in field service.Failure ordinate ()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. cockeyed 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 sup ply 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 = T/R. = MTBFT = total timeR = number of failuresMTTF 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 carve up by the number of devices. It is only when all the parts fail with the same failure mode that MTBF converges to MTTF.= T/N = MTTFT = total timeN = image of units under test.If the MTBF is known, one can calculate the failure rate as the inverse of the MTBF. Theformula for () iswhere r is the number of failures.Once a MTBF is calculated, probability can derive from following equationR(t) = e-t/MTBFConfidence aim 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 instruments, a comprehensive failure rate is desired. The failure r ate calculation can be complicated if there are to a greater extent 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 vat CURVEThe life of a population of units can be divided into three distinct periods. telephone number 1 showsthe reliability bathtub curve which models the cradle to grave instantaneous failurerates vs. time. If we follow the slope from the start to where it begins to flatten out thiscan be considered the first period. The first period is characterized by a decreasing failurerate. It is what occurs during the early life of a population of units. The weaker units dieoff leaving a population that is more rigorous. This first period is also called infantmortality period. The next period is the flat portion of the graph. It is called the normallife. Failures occur more in a random sequence during this time. It is difficult to predictwhich failure mode will manifest, but the rate of failures is predictable. Notice theconstant slope. The third period begins at the point where the slope begins to increase andextends to the end of the graph. This is what happens when units become old and begin tofail at an increasing rate.Reliability prognostics MethodsA slew of time has been spent on developing procedures for estimating reliability of electronic equipment. There are more often than not 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 potpourri 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.= 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 ratewhere, = failure rate in FITs (Number fails in 109 device hours) = Number of distinct possible failure mechanismsk = Number of life tests being combinedxi = Number of failures for a given failure mechanism i = 1, 2, TDHj = Total device hours of test time for life test j, j = 1, 2, kAFij = Acceleration factor for appropriate failure mechanism,i = 1, 2, kM = 2(, 2r +2) / 2where,2 = chi straightforward factor for 2r + 2 degrees of freedomr = total number of failures ( xi) = insecurity associated with CL between 0 and 1.2.2 SOLDER PASTE2.1.1 ROLE OF SOLDER PASTE IN REFLO promoteGSolder bedcover is a combination debauch of a flux composition and a highly grinded, powdered solder metal alloy that is normally used in the electronics industry to mystifying processes. And also it is call as a attachment strong suit between the device interconnection features and the PCB it ego. The components of a solder paste are particularly designed for excellent opinion and reflow characteristics.In normal case of the open air mount soldering process involves placing the substrate and a small arrive 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 PASTESelection 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 pasteThe tendency to form voidsThe properties of the flux medium of the solder pasteAlpha particle emission rateThe design of the print to be used for publishThermal properties of the solder pasteElectrical properties of the solder pasteCHAPTER 03EXPERIMENTS3.1 MATERIALS AND METHODOLGYSOLDER PASTEBasically I used solder paste in same procedure. The details of solder paste used in the experiment are given in the following tableTYPE OFSOLDERPASTEALLOYSCODING corpuscleSIZEMETALLOADINDS1Sn95.5Ag4Cu0.5S2Sn42Bi57Ag1Table 3.1.1 types of solder paste used in experimentFor this project all above solder paste should be in a container with appropriate labelling and identification on it to distinguish it from the atomic number 50 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 borderline four hours before doing the solder paste impression. 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 cut down 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 excise the final results of the project.SOLDER PASTE mental pictureIMPORTANT OF SOLDER PASTE PRINTING come on mount technology (SMT) is used extensively in the electronics industry. Surface mount components are potentially more reliable products can be designed and manufactured usi ng 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 transaction 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 nominate 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 PARAMETERSSome of the following parameters are very important to printing process.STENCILStencils are using for the solder paste post 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. slackly a stencil is mading from cupper or nickel 12.ENVIRONMENTALde tritus and dirt from the air that will reach the PCBs and stencils can be defects slimy wet ability in the reflow soldering process. So PCBs should be stored in sealed packages and cleaned before use.SOLDER PASTESolder paste qualify must be controlled to achieve a maximum production results. Some of the factors are given to a lower place 12.Percent of metalViscosity go underSolder ballsFlux activity working life and shelf lifeSTENCIL PRINTING PARAMETERSStencil 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. wipe pressure = 8kgSqueegee speed = 20 mm/sSeparation speed = 100%Printing gap = 0.0 mmThese factors and limit can be change for our project purposeSOLDER PASTE PRINTING EQUIPMENT AND PROCESSFigure 3.2.4.1 DEK 260 stencil printing machineThe DEK 260 stencil printing machine is used to print solder paste on the circuit board. This DEK 260 stencil printi ng machine has two main functions.Registers the position of the product screen with in the print headPositioning the circuit board below the stencil, to cook for the print cycle.The boards to be print are supported on magnetised 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(p) to get metal stencil, so circuit boards are printed by hand, below procedure followed to print PCBPut weights onto the stencil to fix itroll the wipe over the stencilsolder paste presses through the aperture onto PCBseparate stenciltwo circuit boards are printed with solder paste for each solder paste types. Totally 4 circuit boards printed.SOLDER PASTE REFLOWPROCESS/visibilityFigure 3.3.1 reflow ovenTo 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 regulateIn this district 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 prehe at partition off 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 ZONEIt 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 ZONEIn 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 tha n the manufactures specification it also affect the circuit boards quality.3.3.4 COOLING ZONEIn 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. regularise 1 220Zone 2 clxxxZone 3 170Zone 4 190Zone5 233Zone 6 233Totally 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 reflowSET UP EVENT DETECTORThe constructed PCBs were connected with event detector by ribbon data lineage. Ribbon rail line addressed according to Analysis tech STD series event detectors manual of arms . pins 1 to 32 function as source point and pins 33 to 37 function as ground point.To obtain closed eyeh ole circuit to monitor the behaviour of PCB components, PCB boards 1, 2, 3 and 4 connected to cable 1,2,33 and 34 respectively.Ribbon cableAfter 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 fix for data acquisitionINVESTICATING RELIABILITY OF SOLDER JOINT UNDER VIBRATION CHAMERIn this study, PCBs were used in Variable Frequency Vibration raise 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