Cyclic Thermal Loading Conditions Research Articles

Optimal Design of Thermal Cycling Reliability for Plastic Ball Grid Array Assembly Via Finite Element Method and Taguchi Method

Abstract A finite element simulation analysis model was developed for a plastic ball grid array (PBGA) assembly to analyze its behavior under thermal cyclic loading conditions. The stress distribution in the SAC305 solder joints at different locations within the array was investigated by using ANAND constitutive equations. Subsequently, the thermal fatigue life of the key solder joints was quantified. The study also examined the influence of the solder joint diameter, substrate thickness, solder joint height, printed circuit board (PCB) thickness, and mold compound height on solder joint stress. Optimization of assembly parameters was achieved through the application of the Taguchi method. An extensive analysis was conducted using different assembly parameter combinations, employing the L9(34) orthogonal array design to explore the thermal cycling effects. The computed average Von Mises stress Δσ for the critical thin-layer elements of solder joints located in hazardous positions within the assembly was notably affected by variations in the solder joint height, substrate thickness, solder joint diameter, and mold compound height. This impact ranked in descending order of significance as solder joint height, substrate thickness, solder joint diameter, and mold compound height. The optimal parameter combination determined was a solder joint height of 0.70 mm, a solder joint diameter of 0.85 mm, a substrate thickness of 0.51 mm, and a mold compound height of 1.12 mm. Implementing this optimized configuration led to a significant 4.07% reduction in average stress Δσ for the critical thin-layer elements within hazardous solder joints. Moreover, the extension of the thermal fatigue life was notably improved, achieving an impressive 51.72% increase.

Multi-Scale Modeling of the Thermo-Mechanical Behavior of Cast Iron

This work presents a multi-scale modelling framework for thermo-mechanical behaviour of Compacted Graphite Iron cast iron. A general thermo-elasto-visco-plastic model is developed to describe the matrix (pearlite) behavior under thermo-mechanical cyclic loading, for which the parameters are identified from tests on pearlitic steel. The pearlite model takes into account the temperature dependent rate-dependency and kinematic hardening. The importance of properly accounting for the graphite anisotropy is emphasised, for which a numerical procedure for estimating the local anisotropy directions from the graphite particle geometry and experimental observations is proposed. A high quality conforming finite element mesh is generated on a representative volume element using discrete voxelized microstructural data in combination with signed distance functions from the interfaces. For fully constraint thermal cyclic loading conditions with different holding times, the capabilities of the developed multi-scale model are demonstrated at both scales: the macroscale, where the simulation results are in very good agreement with the experimental data, and the microscale, providing the evolution of local fields.

Research on the reliability of Micro LED high-density solder joints under thermal cycling conditions

For the purpose of studying the effect of high-density, small-size solder joints on the thermal fatigue life of display devices, a 3D model of the corresponding device structure is established, using finite element analysis methods, and using Anand constitutive equations and Coffin-Manson life prediction models. The equivalent stress and strain change law of an indium solder joint with a diameter of 10 μm under thermal cycling loading conditions is explored, and the key position of the solder joint damage is inferred based on the simulated strain cloud diagram. In addition, the influence of different bump height, bump contact area and Under-Bump Metallization (UBM) thickness on the thermal fatigue life of solder joints is studied separately. The final simulation results show that the location where the solder joint may be damaged first is at the point on the outer side where the solder joint is connected to the UBM on the edge away from the center point. The height of the bump and the contact area of the bump have a significant effect on its thermal fatigue life. In the actual experiment, we should focus on the impact of this aspect.

Proposal of a Thermal Fatigue Damage Evaluation Method for Ceramic Thermal Barrier Coating Systems.

In recent years, the application of thermal barrier coatings to the components used in gas turbines for thermal power generation has become indispensable as higher inlet temperatures for requirement to further improve the efficiency of thermal power generation. Thermal barrier coatings, generally referred to as TBCs, consist of a top coat, which is a thermal barrier layer, and a bond coat, which improves the adhesion strength between the TC and the base material. As the development of new thermal barrier materials is progressed, it is also demanded to clarify the stress and damage behavior of TBCs under the complex thermal fatigue loading conditions in actual gas turbine operation. In this study, comprehensive finite element analysis is performed on a TBC system under cyclic thermal fatigue loading conditions with temperature and stress variations to clarify the deformation behavior and crack initiation life of the TBC, and to develop a fatigue life evaluation method for TBCs.

Microwave-enhanced consolidation of zirconia/titanium functionally graded materials

This study aims to fabricate ZrO2/Ti functionally graded materials (FGMs) using microwave-enhanced sintering techniques with a domestic microwave oven. The compositional gradient is expected to make temperature gradient in the materials due to increases in dielectric losses of ZrO2 at high temperatures during consolidation processes. The fabricated ZrO2/Ti FGMs demonstrated the sound microstructures and thermo-mechanical properties under cyclic thermal shock loading conditions. Finite element analysis (FEA) with mean-field micromechanics was conducted to examine the experimental results.

Advanced Online Moisture Measurements in Transformer Insulation Using Optical Sensors

The reliable moisture determination in a power transformer is still a challenge for utilities and large power transformer operators. The presence of high moisture can cause serious problems, such as severely reducing the remaining useful life and the operational capability of a transformer. The large insulation structure and slow dynamic moisture migration between cellulose and insulating fluid make it difficult to determine the true moisture level. Fiber optics based sensors offer superior sensing characteristics as compared with other techniques. A key advantage of using fiber optic sensors is their ability to be inserted into the winding structure. However, this is a relatively new technology and so extensive research and testing is required to understand how their measurement is affected by the operation of a transformer, and in particular by any sudden changes during a stepped load. In this work, the application of optical fiber Bragg grating based sensors is investigated under the influence of step cyclic thermal loading condition. The test is similar to the test performed by CIGRE WG D1.52 for evaluating different capacitive water activity probes. The tested optical sensors, coated with polyimide material for moisture sensing, are found to be suitable in comparison with commercial sensors and can be effectively used for moisture measurements in different insulated transformers.

Fracture behavior of magnesia refractory materials under combined cyclic thermal shock and mechanical loading conditions

AbstractTo investigate the effect of cyclic thermal shock and mechanical loading on the fracture behavior of magnesia refractories showing different brittleness, the as‐received and cyclic thermally shocked specimens are subjected to monotonic and cyclic wedge splitting test. The whole duration of test is monitored by digital image correlation and acoustic emission. Both thermal and mechanical fatigue resistance increase with the reduction of brittleness. Repetitive thermal shock results in pronounced reduction of strength. However, the specific fracture energy and nonlinearity increase after exposure to thermal shock due to the expanded micro‐crack network inducing the development of a significant fracture process zone. Periodic loading mainly leads to the decrease of strain bearing capacity, as the fatigue loads favor the extension of crack tip instead of fracture process zone expansion. The combined application of periodic thermal shock and mechanical loads gives a new insight into the progressive damage behavior of refractory under critical conditions.

Behaviour of carbon nanotubes-Cr2O3 thermal barrier coatings in actual boiler

ABSTRACTHot corrosion behaviour of Carbon Nanotubes (CNT) reinforced Cr2O3 composite coatings have been investigated in actual boiler environment of a thermal power plant at 900°C under cyclic thermal loading conditions. The CNT content was varied from 1 to 8 wt-% and the coatings were deposited with the high-velocity oxy-fuel method. The comparative effects of variation in CNT content (from 1 to 8 wt-%) on hot corrosion behaviour were studied by weight change analysis and corrosion products were analysed with X-ray diffraction, scanning electron microscopy, energy dispersive and cross-sectional analysis techniques. The results confirmed that variation in CNT content enhanced the corrosion resistance of surface coatings in actual boiler environment at elevated temperature. The coatings showed lower weight gain along with the formation of protective oxide scales during the experiment. Reduction in corrosion rates during hot corrosion was observed with an increase in CNT content in the coating matrix.

An analysis of the reliability and design optimization of aluminium ribbon bonds in power electronics modules using computer simulation method

Ribbon bonding technique has recently been used as an alternative to wire bonding in order to improve the reliability, performance and reduce cost of power modules. In this work, the reliability of aluminium and copper ribbon bonds for an Insulated Gate Bipolar Transistors (IGBT) power module under power cycling is compared with that of wire bonds under power and thermal cycling loading conditions. The results show that a single ribbon with a cross section of 2000 μm × 200 μm can be used to replace three wire bonds of 400 μm in diameter to achieve similar module temperature distribution under the same power loading and ribbon bonds have longer lifetime than wire bonds under cyclic power and thermal cycling conditions. In order to find the optimal ribbon bond design for both power cycling and thermal cycling conditions, multi-objective optimization method has been used and the Pareto optimal solutions have been obtained for trade off analysis.

Flaw Tolerance Assessment for Low-Cycle Fatigue of Stainless Steel

According to Appendix L of the Boiler and Pressure Vessel Code Section XI, flaw tolerance assessment is performed using the stress intensity factor (SIF) even for low-cycle fatigue. On the other hand, in Section III, the fatigue damage is assessed using the design fatigue curve (DFC), which has been determined from strain-based fatigue tests. Namely, the stress is used for the flaw tolerance assessment. In order to resolve this inconsistency, in the present study, the strain intensity factor was used for crack growth prediction. First, it was shown that the strain range was the key parameter for predicting the fatigue life and crack growth. The crack growth rates correlated well with the strain intensity factor even for the low-cycle fatigue. Then, the strain intensity factor was applied to predict the crack growth under uniform and thermal cyclic loading conditions. The estimated fatigue life for the uniform cyclic loading condition agreed well with that obtained by the low-cycle fatigue tests, while the fatigue life estimated for the cyclic thermal loading condition was longer. It was shown that the inspection result of “no crack” can be reflected to determining the future inspection time by applying the flaw tolerance analysis. It was concluded that the flaw tolerance concept is applicable not only to the plant maintenance but also to plant design. The fatigue damage assessment using the design fatigue curve can be replaced with the crack growth prediction.

A Novel Acceleration-Factor Equation for Packaging-Solder Joint Reliability Assessment at Different Thermal Cyclic Loading Rates

AbstractAcceleration-factor (AF) equations have been developed to rapidly predict product lifetime, and the most widely used equation is Norris-Landzberg (N-L) equation. In recent years, some researchers have found that the current AF equation does not accurately predict the experimental results for thermal cyclic loading at high ramp rates; indeed, it may yield the opposite results, due to the changing effect of the solder strain rate at different ramp rates. Modifying the current AF equation to better assess product reliability has thus become an important task for researchers.In this study, a novel AF equation was developed from a wafer level chip-scale package (WLCSP) under different thermal cyclic loadings. The frequency term used in the N-L equation was replaced with a new term in the proposed AF equation to distinguish between the effects of ramp rate and dwell time under thermal cyclic loading conditions. Proposed AF equation showed a high level of correlation with the simulation and test results for various thermal cyclic loadings. In addition, the proposed AF equation was validated by confirming the consistency of its results with experimental data on a range of packages and thermal-cycling profiles reported in the literature.

Mechanical characteristics approach on W/Cr nano-interface structure

The objective of this article is to provide an experimental test and evaluation on mechanical characteristics of the W/Cr interface. The elastic modulus and hardness of the sample are measured by a nanoindentation tester. The test results show that the elastic modulus and hardness of the sample are nonlinear with respect to the depth h of the interface structure, unlike the usual approximate horizontal linear relationship as expected. To understand the bonding characteristics between W and Cr in nanoscale, the nano-scratch test is conducted considering the influence of thermal cycling load on the sample. The test results show that interfacial bonding strengths are different between samples under different thermal cycling loading conditions. It implies that the thermal loading has the potential probability to reduce the bonding reliability of the W/Cr interface. It builds a basis for future work of further investigations on mechanical properties of W/Cr interface structure.

The Reliability of Microalloyed Sn-Ag-Cu Solder Interconnections Under Cyclic Thermal and Mechanical Shock Loading

In this study, the performance of three microalloyed Sn-Ag-Cu solder interconnection compositions (Sn-3.1Ag-0.52Cu, Sn-3.0Ag-0.52Cu-0.24Bi, and Sn-1.1Ag-0.52Cu-0.1Ni) was compared under mechanical shock loading (JESD22-B111 standard) and cyclic thermal loading (40 ± 125°C, 42 min cycle) conditions. In the drop tests, the component boards with the low-silver nickel-containing composition (Sn-Ag-Cu-Ni) showed the highest average number of drops-to-failure, while those with the bismuth-containing alloy (Sn-Ag-Cu-Bi) showed the lowest. Results of the thermal cycling tests showed that boards with Sn-Ag-Cu-Bi interconnections performed the best, while those with Sn-Ag-Cu-Ni performed the worst. Sn-Ag-Cu was placed in the middle in both tests. In this paper, we demonstrate that solder strength is an essential reliability factor and that higher strength can be beneficial for thermal cycling reliability but detrimental to drop reliability. We discuss these findings from the perspective of the microstructures and mechanical properties of the three solder interconnection compositions and, based on a comprehensive literature review, investigate how the differences in the solder compositions influence the mechanical properties of the interconnections and discuss how the differences are reflected in the failure mechanisms under both loading conditions.

Effect of zirconium addition in HVOF sprayed Ni–20Cr coating

High velocity oxyfuel spraying was used to deposit Ni–20Cr coating on an ASTM-SA213-T22 boiler steel with and without 1%Zr addition. High temperature oxidation behaviour of both coatings was evaluated under cyclic thermal loading conditions at an elevated temperature of 900°C. Mass change data were measured to formulate the kinetics of oxidation for the specimens. The exposed specimens were characterised by X-ray diffraction and field emission scanning electron microscopy/energy dispersive spectroscopy. It was observed that mass loss was reduced by 46% after the Zr addition in the commercially available Ni–20Cr coating. The formation of Zr rich pegs in the blended coating might have resulted in beneficial results.

An analytical procedure for estimating field lifetime and failure rate of electronic packages

To understand the reliability characteristics of electronic packages under field conditions, accelerated life tests (ALT) with higher stress levels are needed in practice. Instead of the time-consuming and costly ALT, an analytical procedure based on finite element simulation and a Weibull statistical method to estimate the lifetime and failure rate of electronic packages subjected to thermal cycling loadings is proposed in the present study. To consider uncertainties, geometric parameters and material properties are assumed as random variables and incorporated into numerical simulation. The result shows that the mean time to failure (MTTF) of a studied electronic package under a specific thermal cycling loading condition can be predicted accurately. From either the proposed analysis or based on a particular model found in literature, the acceleration factor (AF) can be predicted accurately as well. Furthermore, according to the outcome from the Weibull statistical method, the failure rate under either the field or a particular test condition can be determined. Accordingly, the MTTF and failure rate of the package under field conditions can be estimated from the result of a simulated accelerated test as well as the AF model. The present study indicates that the proposed analytical procedure can help engineers evaluate the reliability of electronic packages rapidly and effectively.

Bond strength of RC beams subjected to cyclic thermal loading

Bond strength of rebar lap splice in reinforced concrete beams has been investigated experimentally when they are subjected to cyclic thermal loading. One hundred and eleven RC beams of 100×150×1200mm size were tested under flexure for the bond behavior of splices under four point loading. The beams were reinforced in tension zone only with a single Thermomechanically treated (TMT) steel bar of 8, 10 and 12mm diameter. The beams were subjected to a number of thermal cycles varying from 7 to 28 with peak temperature taken as 100, 200 and 300°C. The effects of thermal cycles on the crack pattern, failure mechanism, first crack load and the bond strength have been discussed. The loss in bond strength is found to be more for 12mm rebar diameter which is due to the splitting of concrete cover due to the lateral expansion of rebar. Beams reinforced with 8 and 10mm diameter bar exhibited comparatively less damaging effects. The bond strength of the beams at lower temperature cycles of 100 and 200°C is either at par with control or even more but it reduces by up to 44% at higher temperature (300°C) depending on the severity of thermal loading. The results of study emphasize the need for developing appropriate guidelines for the design of RC structural elements used in comparatively high temperature environment with cyclic thermal loading conditions.

Meso‐Macro Modelling of Coated Forming Tools under Thermal Shock Conditions

AbstractIn hybrid‐forming processes workpieces are heated up before forming in order to reduce the forming forces. They are innovative methods for the production of components with graded properties, particularly with regard to tailored material properties and geometrical shape. During service life the forming tools are subjected to cyclic thermal shock loading conditions which can result into damage and failure. For improvement of the tool durability in the hybrid‐forming process coated forming tools with multilayered coating systems are considered to be applied in future.This contribution shows the actual state of work for the development of a twoscale FE model for the simulation of the multilayered coated forming tool. Within this model the three‐dimensional model of the forming tool builds the macromodel. On the macrolevel the multilayered coating is discretized with one element over the coating thickness. The mesomodel of the coating considers the actual layer design with metallic and ceramic layers. The macro‐meso transition is realized with a Taylor‐assumption. As the microscale is not considered in our model, the constitutive equations are formulated on the mesoscale. The meso‐macro transition is done using volume averaging procedures. Furthermore, a damage model is included for particular layers. The scalar damage variable is used in a thermo‐mechanical coupled model for simulation of a reduced heat transfer through a partially damaged layer. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of creep–fatigue life prediction models for nickel-based super alloys

Creep fatigue is the main damage form of engine parts operating under both cyclic mechanical and thermal loading conditions. In the present work time-dependent creep and cycle-dependent fatigue of nickel-based super alloys is discussed. Three different kinds of creep–fatigue life models are investigated for the nickel-based super alloys. Effects of temperature, loading ratio and loading hold time to material failure are considered. Comparison with experiments reveals that the linear accumulation concept based on Forman model provides reasonable results on the creep–fatigue interaction if the life is dominated by mechanical fatigue damage. For higher loading ratios, however, deviations become significant. In the lower frequency region the modified FCE models and Saxena models give more reasonable predictions, but show large discrepancy to tests with hold time. The modified Saxena model suggested in the present work contains a separate term for hold time effects and agrees with the experimental observations more accurately.

Performance study of K e factors in simplified elastic plastic fatigue analyses with emphasis on thermal cyclic loading

As code-based fully elastic plastic code conforming fatigue analyses are still time consuming, simplified elastic plastic analysis is often applied. This procedure is known to be overly conservative for some conditions due to the applied plastification (penalty) factor K e . As a consequence, less conservative fully elastic plastic fatigue analyses based on non-linear finite element analyses (FEA) or simplified elastic plastic analysis based on more realistic K e factors have to be used for fatigue design. The demand for more realistic K e factors is covered as a requirement of practical fatigue analysis. Different code-based K e procedures are reviewed in this paper with special regard to performance under thermal cyclic loading conditions. Other approximation formulae such as those by Neuber, Seeger/Beste or Kuehnapfel are not evaluated in this context because of their applicability to mechanical loading excluding thermal cyclic loading conditions typical for power plant operation. Besides the current code-based K e corrections, the ASME Code Case N-779 (e.g. Adam’s proposal) and its modification in ASME Section VIII is considered. Comparison of elastic plastic results and results from the Rules for Nuclear Facility Components and Rules for Pressure Vessels reveals a considerable overestimation of usage factor in the case of ASME III and KTA 3201.2 for the examined examples. Usage factors according to RCC-M, Adams (ASME Code Case N-779), ASME VIII (alternative) and EN 13445-3 are essentially comparable and less conservative for these examples. The K v correction as well as the applied yield criterion (Tresca or von Mises) essentially influence the quality of the more advanced plasticity corrections (e.g. ASME Code Case N-779 and RCC-M). Hence, new proposals are based on a refined K v correction.

High-Temperature Erosion-Corrosion Performance of High-Velocity Oxy-Fuel Sprayed Ni-20 Cr Coating in Actual Boiler Environment

The high-velocity oxy-fuel (HVOF) spray technique was used to deposit Ni-20Cr coating on a commonly used boiler steel ASTM A213 347H. The specimens with and without coating were exposed to the super heater zone of a thermal power plant boiler at a temperature of 973 K (700 °C) under cyclic conditions to ascertain their erosion-corrosion (E-C) behavior. High-temperature oxidation behavior of the specimens was also evaluated under cyclic thermal loading conditions at an elevated temperature of 1173 K (900 °C). Mass change data and thickness loss were measured to formulate the kinetics of E-C/oxidation for the specimens. The exposed specimens were characterized by X-ray diffraction (XRD) and field emission–scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS). The uncoated steel suffered higher E-C in comparison with its coated counterpart in terms of mass loss as well as thickness loss. It was observed that overall mass loss was reduced by 31 pct and thickness loss by 44 pct after the application of the coating. The possible formation of Cr2O3 phase in the coated substrate may be suggested to contribute to better E-C behavior. During air oxidation exposures, the coating was found to be intact with only marginal spallation of its oxide scales, which is an indicator of good adhesion between the coating and substrate steel. The air oxidation mass change data indicated that the coating enhanced the oxidation resistance of the steel by 85 pct.