DEVELOPMENT OF MOIRÉ INTERFEROMETRY FOR REAL-TIME OBSERVATION OF NONLINEAR THERMAL DEFORMATIONS OF SOLDER AND SOLDER ASSEMBLY

An experimental apparatus using moiré interferometry is developed to characterize the thermo-mechanical behavior of solder joints. A compact moiré interferometer is combined with an environmental chamber to allow real-time observation of non-linear and time-dependent solder and solder assemblies. The first apparatus is based on convection heating and cooling to simulate an accelerated thermal cycling (ATC) condition. Vibrations caused by an environmental chamber are circumvented by unique rigid links that connect the specimen to the moiré interferometer. Displacement fields are documented while the chamber is being operated. The system is utilized to analyze thermo-mechanical behavior of a ceramic ball grid array package assembly and a plastic ball grid array package assembly. The effect of thermal cycling on the accumulated permanent deformation is documented, which reveals the temperature-dependent non-linearity of solder joints. The second apparatus is based on conduction heating and cooling to achieve a high ramp rate. A special chamber is designed and fabricated using a high power thermoelectric cooler to achieve the desired ramp rate. The system is utilized to investigate the time-dependent behavior of solder joints. A new solder joint configuration is designed and fabricated to be tested with the conduction based apparatus. The specimen is an extension of the conventional bi-material joint configuration but the unique design offers two important features; it negates the inherent shortcoming from cross sectioning required in moiré interferometry and produces a virtually uniform shear strain field at the solder joint. The deformation of solder joint is documented at a controlled ramp rate over several thermal cycles. The experimental results are analyzed and compared with those of Finite Element analysis to investigate the validity of solder constitutive models available in the literatures

Design of Experiment Analysis of an Electronics Package Lid Using Finite Element Analysis

A design of experiment analysis is reported on data from warpage simulations using finite element analysis of a lidded electronics package. Warpage in a lid of an optical electronics package can detrimentally affect the reliability of the package as well as its optical performance. The present study focuses on the variety of materials and designs of lids relevant to recent technologies in electronics packaging. The finite element analysis (FEA) formulation in this study accurately predicts deformation and warpage in the elastic region with optimal computational time achieved through a choice of boundary conditions and mesh sensitivity studies. The results from FEA are compared to analytical calculations made using the classical laminate plate theory (CLPT) as well as the modified Suhir’s theory. It is observed that FEA results are more accurate as they account for the performance of die attach/ underfill materials regardless of the small thickness of the layer. The FEA data are finally used to conduct a design of experiments (DOE) analysis to investigate the influence of 3 distinct designs and 6 material choices on warpage of a lid. The analysis indicates that there is no significant interaction between the two parameters expected to affect the warpage in the lid. Material properties of the lid are found to have a greater effect on the warpage of the lid as compared to variabilities introduced in lid designs in this study. The FEA simulations performed consider only material behavior within the elastic limit and, in some situations, plastic deformation may occur which is more permanent and as such requires a more comprehensive analysis in the plastic region to enhance the data set for DOE studies

ADVANCEMENT OF MOIRÉ INTERFEROMETRY FOR RATE-DEPENDENT MATERIAL BEHAVIOR AND MICROMECHANICAL DEFORMATIONS

Moiré interferometry is an optical technique to map full field in-plane deformations with extremely high resolution and signal to noise ratio. The technique is advanced and implemented to study the rate-dependent thermo-mechanical behavior of Sn-based Pb-free solder alloys and micromechanical deformations. In Part I, the mechanical/optical configuration of moiré interferometry for real-time observation of thermal deformations is enhanced to provide measurement capabilities required for the analyses. Two most notable advancements are (1) development of a conduction-based thermal chamber for a wide range of ramp rates with accurate temperature control, and (2) implementation of microscope objectives in the imaging system to observe a microscopic field of view. The advanced system is implemented to analyze the anisotropic behavior of Sn-based Pb-free solder alloys. A novel copper-steel specimen frame is developed to apply a controlled loading to single-grain solder joints. After measuring the grain orientation by electron backscatter diffraction (EBSD), detailed in-situ deformation evolutions and accumulated deformations of solder alloys are documented during a thermal cycle of -40 °C to 125 °C. The results quantify grain orientation-dependent deformations that can lead more accurate anisotropic constitutive properties of Sn-based Pb-free solder alloys. In Part II, an advanced immersion microscopic moiré interferometry system based on an achromatic configuration is developed and implemented for higher displacement sensitivity and spatial resolution. In order to achieve the desired displacement resolution, a high frequency grating (2500 lines/mm) is fabricated on a silicon substrate using lithography first. The square profile is subsequently modified by reactive-ion etching so that it can be used to produce a specimen grating by replication. Secondly, the algorithm of the optical/digital fringe multiplication method is improved to further enhance the measurement resolution of the immersion microscopic moiré interferometry. The system and the noise-free grating are used to analyze thermal deformations of micro-solder bumps. With the basic contour interval of 200 nm, the displacement resolution of 25 nm is achieved with the multiplication factor of 8

Dynamic Mechanical and Failure Properties of Solder Joints

Ph.DDOCTOR OF PHILOSOPH

The durability of solder joints under thermo-mechanical loading; application to Sn-37Pb and Sn-3.8Ag-0.7Cu lead-free replacement alloy

Solder joints in electronic packages provide mechanical, electrical and thermal connections. Hence, their reliability is also a major concern to the electronic packaging industry. Ball Grid Arrays (BGAs) are a very common type of surface mount technology for electronic packaging. This work primarily addresses the thermo-mechanical durability of BGAs and is applied to the exemplar alloys; traditional leaded solder and a popular lead-free solder. Isothermal mechanical fatigue tests were carried out on 4-ball test specimens of the lead-free (Sn-3.8Ag-0.7Cu) and leaded (Sn-37Pb) solder under load control at room temperature, 35°C and 75°C. As well as this, a set of combined thermal and mechanical cycling tests were carried out, again under load control with the thermal cycles either at a different frequency from the mechanical cycles (not-in-phase) or at the same frequency (both in phase and out-of-phase). The microstructural evaluation of both alloys was investigated by carrying out a series of simulated ageing tests, coupled with detailed metallurgical analysis and hardness testing. The results were treated to produce stress-life, cyclic behaviour and creep curves for each of the test conditions. Careful calibration allowed the effects of substrate and grips to be accounted for and so a set of strain-life curves to be produced. These results were compared with other results from the literature taking into account the observations on microstructure made in the ageing tests. It is generally concluded that the TMF performance is better for the Sn-Ag-Cu alloy than for the Sn-Pb alloy, when expressed as stress-life curves. There is also a significant effect on temperature and phase for each of the alloys, the Sn-Ag-Cu being less susceptible to these effects. When expressed as strain life, the effects of temperature, phase and alloy type are much diminished. Many of these conclusions coincided with only parts of the literature and reasons for the remaining differences are advanced

Thermo-mechanical reliability studies of lead-free solder interconnects

N/ASolder interconnections, also known as solder joints, are the weakest link in electronics packaging. Reliability of these miniature joints is of utmost interest - especially in safety-critical applications in the automotive, medical, aerospace, power grid and oil and drilling sectors. Studies have shown that these joints' critical thermal and mechanical loading culminate in accelerated creep, fatigue, and a combination of these joints' induced failures. The ball grid array (BGA) components being an integral part of many electronic modules functioning in mission-critical systems. This study investigates the response of solder joints in BGA to crucial reliability influencing parameters derived from creep, visco-plastic and fatigue damage of the joints. These are the plastic strain, shear strain, plastic shear strain, creep energy density, strain energy density, deformation, equivalent (Von-Mises) stress etc. The parameters' obtained magnitudes are inputted into established life prediction models – Coffin-Manson, Engelmaier, Solomon (Low cycle fatigue) and Syed (Accumulated creep energy density) – to determine several BGA assemblies' fatigue lives. The joints are subjected to thermal, mechanical and random vibration loadings. The finite element analysis (FEA) is employed in a commercial software package to model and simulate the responses of the solder joints of the representative assemblies' finite element models. As the magnitude and rate of degradation of solder joints in the BGA significantly depend on the composition of the solder alloys used to assembly the BGA on the printed circuit board, this research studies the response of various mainstream lead-free Sn-Ag-Cu (SAC) solders (SAC305, SAC387, SAC396 and SAC405) and benchmarked those with lead-based eutectic solder (Sn63Pb37). In the creep response study, the effects of thermal ageing and temperature cycling on these solder alloys' behaviours are explored. The results show superior creep properties for SAC405 and SAC396 lead-free solder alloys. The lead-free SAC405 solder joint is the most effective solder under thermal cycling condition, and the SAC396 solder joint is the most effective solder under isothermal ageing operation. The finding shows that SAC405 and SAC396 solders accumulated the minimum magnitudes of stress, strain rate, deformation rate and strain energy density than any other solder considered in this study. The hysteresis loops show that lead-free SAC405 has the lowest dissipated energy per cycle. Thus the highest fatigue life, followed by eutectic lead-based Sn63Pb37 solder. The solder with the highest dissipated energy per cycle was lead-free SAC305, SAC387 and SAC396 solder alloys. In the thermal fatigue life prediction research, four different lead-free (SAC305, SAC387, SAC396 and SAC405) and one eutectic lead-based (Sn63Pb37) solder alloys are defined against their thermal fatigue lives (TFLs) to predict their mean-time-to-failure for preventive maintenance advice. Five finite elements (FE) models of the assemblies of the BGAs with the different solder alloy compositions and properties are created with SolidWorks. The models are subjected to standard IEC 60749-25 temperature cycling in ANSYS 19.0 mechanical package environment. SAC405 joints have the highest predicted TFL of circa 13.2 years, while SAC387 joints have the least life of circa 1.4 years. The predicted lives are inversely proportional to the magnitude of the areas of stress-strain hysteresis loops of the solder joints. The prediction models are significantly consistent in predicted magnitudes across the solder joints irrespective of the damage parameters used. Several failure modes drive solder joints and damage mechanics from the research and understand an essential variation in the models' predicted values. This investigation presents a method of managing preventive maintenance time of BGA electronic components in mission-critical systems. It recommends developing a novel life prediction model based on a combination of the damage parameters for enhanced prediction. The FEA random vibration simulation test results showed that different solder alloys have a comparable performance during random vibration testing. The fatigue life result shows that SAC405 and SAC396 have the highest fatigue lives before being prone to failure. As a result of the FEA simulation outcomes with the application of Coffin-Manson's empirical formula, the author can predict the fatigue life of solder joint alloys to a higher degree of accuracy of average ~93% in an actual service environment such as the one experienced under-the-hood of an automobile and aerospace. Therefore, it is concluded that the combination of FEA simulation and empirical formulas employed in this study could be used in the computation and prediction of the fatigue life of solder joint alloys when subjected to random vibration. Based on the thermal and mechanical responses of lead-free SAC405 and SAC396 solder alloys, they are recommended as a suitable replacement of lead-based eutectic Sn63Pb37 solder alloy for improved device thermo-mechanical operations when subjected to random vibration (non-deterministic vibration). The FEA simulation studies' outcomes are validated using experimental and analytical-based reviews in published and peer-reviewed literature.N/

A THERMOMECHANICAL FATIGUE LIFE PREDICTION METHODOLOGY FOR BALL GRID ARRAY COMPONENTS WITH REWORKABLE UNDERFILL

Underfill materials were originally developed to improve the thermo-mechanical reliability of flip-chip devices due to the large coefficient of thermal expansion (CTE) mismatch between the silicon die and substrate. More recently, underfill materials, specifically reworkable underfills, have been used to improve reliability of second level interconnects in ball grid array (BGA) packages in harsh end-use environments such as automotive, military and aerospace. In these environments, electronic components are exposed to mechanical shock, vibration, and large fluctuations in temperatures. Although reworkable underfills improve the reliability of BGA components under mechanical shock and vibration, some reworkable underfills have been shown to reduce reliability during thermal cycling environments. Consequently, this research employs experimental and numerical approaches to investigate the impact of reworkable underfill materials on thermomechanical fatigue life of solder joints in BGA packages. In the first section of the analysis, material characterization of a reworkable underfill is performed to determine appropriate material models for reworkable underfills. In the second analysis section, a variety of underfill materials with different properties are exposed to harsh and benign thermal cycles to determine the stress state responsible for reducing fatigue life of solder joints in BGA packages. In the final analysis section, simulations are performed on the BGAs with reworkable underfill to develop a fatigue life predication methodology that implements a modified mode separation scheme. The model developed in this work provides a working fatigue life approach for BGA packages with reworkable underfills exposed to thermal loading. The results of this study can be utilized by the automotive, military, and aerospace industries to optimize underfill material selection process and provide reliability assessment of BGA components in real world environments

New advances in vehicular technology and automotive engineering

An automobile was seen as a simple accessory of luxury in the early years of the past century. Therefore, it was an expensive asset which none of the common citizen could afford. It was necessary to pass a long period and waiting for Henry Ford to establish the first plants with the series fabrication. This new industrial paradigm makes easy to the common American to acquire an automobile, either for running away or for working purposes. Since that date, the automotive research grown exponentially to the levels observed in the actuality. Now, the automobiles are indispensable goods; saying with other words, the automobile is a first necessity article in a wide number of aspects of living: for workers to allow them to move from their homes into their workplaces, for transportation of students, for allowing the domestic women in their home tasks, for ambulances to carry people with decease to the hospitals, for transportation of materials, and so on, the list don’t ends. The new goal pursued by the automotive industry is to provide electric vehicles at low cost and with high reliability. This commitment is justified by the oil’s peak extraction on 50s of this century and also by the necessity to reduce the emissions of CO2 to the atmosphere, as well as to reduce the needs of this even more valuable natural resource. In order to achieve this task and to improve the regular cars based on oil, the automotive industry is even more concerned on doing applied research on technology and on fundamental research of new materials. The most important idea to retain from the previous introduction is to clarify the minds of the potential readers for the direct and indirect penetration of the vehicles and the vehicular industry in the today’s life. In this sequence of ideas, this book tries not only to fill a gap by presenting fresh subjects related to the vehicular technology and to the automotive engineering but to provide guidelines for future research. This book account with valuable contributions from worldwide experts of automotive’s field. The amount and type of contributions were judiciously selected to cover a broad range of research. The reader can found the most recent and cutting-edge sources of information divided in four major groups: electronics (power, communications, optics, batteries, alternators and sensors), mechanics (suspension control, torque converters, deformation analysis, structural monitoring), materials (nanotechnology, nanocomposites, lubrificants, biodegradable, composites, structural monitoring) and manufacturing (supply chains). We are sure that you will enjoy this book and will profit with the technical and scientific contents. To finish, we are thankful to all of those who contributed to this book and who made it possible.info:eu-repo/semantics/publishedVersio

Plastic Ball Grid Array Solder Joint Reliability Assessment under Combined Thermal Cycling and Vibration Loading Conditions

Concurrent vibration and thermal environment is commonly encountered in the service life of electronic equipment, including those used in automotive, avionic, and military products. Though extensive research exists in literature for solder joint failures due to thermal cycling, limited research has been conducted on investigating solder joint failures due to a combination of vibration and thermal cycling. In this study, experiments were conducted on PBGA assemblies under thermal cycling, vibration loading, and combined thermal cycling and vibration loading conditions. The results showed much earlier PBGA solder joint failure under combined loading compared with either thermal cycling or vibration loading alone. It was found that traditional linear superposition can overpredict the solder joint fatigue life since it neglects the interaction of the vibration and thermal cyclic loadings. An incremental damage superposition approach using finite element analysis was applied to PBGA solder joint reliability assessment. This approach can model the nonlinear interactions between vibration loading and thermal cycling. It considers the temperature effect on vibration response and the effect caused by thermomechanical mean stress affects. This approach was validated through experiments and reflects the actual damage trends. Based on the incremental damage superposition approach, a rapid solder joint fatigue life prediction simulation approach for PBGA was also developed for combined temperature cycling and vibration loading conditions. This approach included a thermomechanical stress model and a vibration stress model to analyze the interconnect stress under thermal cycling and vibration loading conditions. The mean stress during thermal cycling was obtained from the response curve. The damage due to two different loadings was then calculated using the generalized strain approach and superposed. This approach was also validated using experimental data. This work has also resulted in a rapid virtual qualification algorithm to predict solder joint reliability under combined temperature and vibration loading conditions. The importance of physics of failure principles in modeling and designing experiments were also explored and addressed. Industry should benefit from this study on reliability prediction, qualification, and accelerated testing design

Rapid Assessment of BGA Fatigue Life Under Vibration Loading

Ball Grid Array (BGA) packages are a relatively new package type and have rapidly become the package style of choice. Much high density, high I/O count semiconductor devices are now only offered in this package style. Designers are naturally concerned about the robustness of BGA packages in a vibration environment when their experience base is with products using more traditional compliant gull or J leaded surface mount packages. Because designers simply do not have the experience, tools are needed to assess the vibration fatigue life of BGA packages during early design stages and not have to wait for product qualification testing, or field returns, to determine if a problem exists. This dissertation emphasizes a rapid assessment methodology to determine fatigue life of BGA components. If time and money were not an issue, clearly one would use a general-purpose finite element program to determine the dynamic response of the printed wiring board in the vibration environment. Once the response of the board was determined, one would determine the location and value of the critical stress in the component of interest. Knowing the critical stress, one would estimate the fatigue life from a damage model. The time required building the FEA model, conducting the analysis, and post-process the results would take at least a few days to weeks. This is too time-consuming, except in the most critical applications. It is not a process that can be used in everyday design and what-if simulations. The rapid assessment approach proposed in this research focuses on a physics of failure type approach to damage analysis and involves global and local modeling to determine the critical stress in the component of interest. A fatigue damage model then estimates the life. Once implemented in software, i.e. the new version of CALCE_PWA, the entire fatigue life assessment is anticipated to be executed by an average engineer in real time and take only minutes to generate accurate results