Electronic Packaging Structures Research Articles

A Kriging Surrogate Model for Ball Grid Array Electronic Packaging With Stochastic Material and Geometrical Parameters

Abstract Ball grid arrays (BGAs) offer significant advantages in the automotive industry, such as their small size and high integration density, making them a promising electronic packaging approach. However, the operating environment of automobiles is more complex compared to other applications, primarily due to vibrations generated by power engines and oscillations caused by pavement roughness. The resonant frequencies of electronic packaging structures play a crucial role in system reliability and safety. However, accurately describing the implicit relationship between system resonant frequencies and material and geometrical parameters can be challenging. A Kriging surrogate model (KSM) is proposed by the combination of the Latin Hypercube stochastic sampling with finite element computation. Four different BGA configurations are established with either the initial values in the deterministic model or the specified sampling interval ranges in the stochastic model. The results of the finite element model (FEM) for BGA electronic packaging are validated and demonstrate qualitative agreement with published literature. The impacts of material and geometrical parameters on the resonant frequencies are investigated and compared. The mean, maximum, minimum, and variance are recorded based on a large database of stochastic samples. The feasibility of KSM for the resonant frequency prediction of BGA is confirmed by its satisfactory accuracy and computational efficiency.

Data-driven electronic packaging structure inverse design with an adaptive surrogate model

PurposeThe conventional design method relies on a priori knowledge, which limits the rapid and efficient development of electronic packaging structures. The purpose of this study is to propose a hybrid method of data-driven inverse design, which couples adaptive surrogate model technology with optimization algorithm to to enable an efficient and accurate inverse design of electronic packaging structures.Design/methodology/approachThe multisurrogate accumulative local error-based ensemble forward prediction model is proposed to predict the performance properties of the packaging structure. As the forward prediction model is adaptive, it can identify respond to sensitive regions of design space and sample more design points in those regions, getting the trade-off between accuracy and computation resources. In addition, the forward prediction model uses the average ensemble method to mitigate the accuracy degradation caused by poor individual surrogate performance. The Particle Swarm Optimization algorithm is then coupled with the forward prediction model for the inverse design of the electronic packaging structure.FindingsBenchmark testing demonstrated the superior approximate performance of the proposed ensemble model. Two engineering cases have shown that using the proposed method for inverse design has significant computational savings while ensuring design accuracy. In addition, the proposed method is capable of outputting multiple structure parameters according to the expected performance and can design the packaging structure based on its extreme performance.Originality/valueBecause of its data-driven nature, the inverse design method proposed also has potential applications in other scientific fields related to optimization and inverse design.

Optimized super-resolution promote accuracy for projection speckle three-dimensional digital image correlation

The camera resolution and electronic noise limit the accuracy of the projection speckle three-dimensional digital image correlation (3D-DIC) which is a non-invasive method to detect the reliability of electronic packaging structure. In this study, a measurement method of super-resolution (SR) reconstruction coupled with projection speckle DIC is proposed. The algorithm based on the maximum a posteriori model for DIC measurement systems was also optimized, and a speckle-specific bimodal prior was proposed to adapt to speckle images. By using optimized SR technology as an image pre-processing technique to enhance the resolution of captured images, the accuracy of measurements is improved. Full-field displacement measurement experiments show that, with suitable magnification and speckle size, the use of SR technology reduces the range of displacement errors from 8 μm to 2 μm. Experiments on step block topography measurements show that the use of SR technology reduces the error between DIC measurements and Moiré interferometry from 5 μm to within 2 μm. Therefore, SR technology can be effectively paired with projection speckle DIC measurements to adapt to various measurement scenarios in the field of electronic packaging reliability testing.

Mechanical properties of Sn–Pb based solder joints and fatigue life prediction of PBGA package structure

Solder joints are generally the weakest part in electronic packaging structure whose fatigue life depends to a large extent on the durability of solder joints. In pursuit of a balance between environmental protection and soldering performance, commonly used Sn–Pb solder should be modified by adding other chemical elements to reduce Pb content. This work aims to investigate the performance of different solder materials and explore the impact of different electronic package structures. Firstly, tensile experiments are performed on three kinds of solders (Sn–Pb, Sn–Pb–In, Sn–Pb–Bi) to obtain their mechanical behavior, and then the constitutive laws of them are calibrated by Anand model. Additionally, finite element method (FEM) is used simulate the response of plastic ball grid array (PBGA) package structure under thermal cycles, and mechanical variables including deformation, equivalent stress, and equivalent strain are analyzed. Finally, Coffin-Manson and Engelmaier equations are adopted to predict the fatigue life of package structures and the effects of various factors such as solder materials, dimensions of components, and welding quality are further investigated. Results reveal that adding Bi into Sn–Pb solder can make the solder joints have better performance. From the perspective of optimum fatigue life, the plastic package thickness is recommended in the range of 0.8 mm–0.9 mm, the chip thickness is recommended as 0.35 mm, the substrate thickness is recommended to be less than 0.34 mm, and the ratio of stand-off height to solder ball diameter should be controlled between 0.6 and 0.7. According to the prediction, the solder ball diameter is suggested to be 0.54 mm so that fatigue life could reach 194 cycles, and the stand-off height for this package structure is suggested to be 0.36 mm so that fatigue life could reach 123 cycles.

Multiprocessing implementations for time-dependent fracture analysis of an electronic packaging structure

Multiprocessing implementations for time-dependent fracture analysis of an electronic packaging structure

Transition Metal β-Diketonate Adhesion Promoters in Epoxy-Anhydride Resin.

Epoxy to copper adhesion supports the reliability of numerous structures in electronic packaging. Compared to substrate pre-treatment, processing and cost considerations are in favor of adhesion promoters loaded in epoxy formulations. In this work, first row transition metal β-diketonates present such a compelling case when added in epoxy/anhydride resins: over 30% (before moisture aging) and 50% (after moisture aging) enhancement in lap shear strength are found using Co(II) and Ni(II) hexafluoroacetylacetonate. From extensive X-ray photoelectron spectroscopy (XPS) analyses on the adhesively failed sample surfaces, increased population of oxygen-containing functional groups, especially esters, is linked to the adhesion improvement. Assisted by XPS depth profile on the fractured epoxy side and in situ Fourier-transform infrared spectroscopy (FTIR), the previously discovered latent cure characteristics endowed by the metal chelates interacting with phosphine catalysts are regarded pivotal for pacing the anhydride consumption and allowing interfacial esterification reactions to occur. Further examinations on the XPS binding energy shifts and dielectric properties of the doped epoxy also reveal metal-polymer coordination that contribute to the adhesion and moisture resistance properties. These findings should stimulate future research of functional additives targeting at cure kinetics control and polar group coordination ideas for more robust epoxy-Cu joints.

Connecting the macroscopic and mesoscopic properties of sintered silver nanoparticles by crystal plasticity finite element method

The stress–strain response of sintered silver nanoparticles (AgNP) materials is precisely characterized in order to adapt for numerical analysis and rational design of electronic packaging structures in this study. A framework of crystal plasticity finite element method (CPFEM) is established based on the mechanism of crystal plastic deformation to describe the mesoscopic structural influence of grain evolution on the macroscopic properties of sintered AgNP materials. Material parameters of crystal plasticity are defined and initial orientations are randomly assigned for sintered AgNP grains. To calibrate the mesoscopic mechanical properties of sintered AgNP by the proposed CPFEM, the results of CPFEM simulations and uniaxial tensile tests subjected to different strain rates and temperatures are compared in terms of the stress–strain curves as the critical macroscopic characteristics. The predicted stress and deformation distributions in the polycrystalline structure demonstrate that the significant inhomogeneity of stress and deformation is caused by the different grain orientations of sintered AgNP. Furthermore, we elucidate the fracture mechanism influenced by the temperature and strain rate and also the effect of initial crystal orientation on the plastic strain of sintered AgNP. This study sheds light on the morphology design of sintered AgNP with optimized mechanical properties and fatigue resistance.

An insight into dynamic properties of SAC305 lead-free solder under high strain rates and high temperatures

The development of high density and high integration of electronic chips puts forward stricter requirements on electronic packaging structures. Under the premise of lead-free rules, Sn-3.0Ag-0.5Cu (SAC305) has developed into a competitive solder material. However, the reliability of its mechanical properties has been attracting much attentions especially under extreme conditions. In this paper, the high-strain rate experiments are performed by a split-Hopkinson pressure bar (SHPB) to realize different plastic strain rate, while the high temperature environment is achieved by incorporating a heating furnace. By combining these two devices, the dynamic responses of solder specimens can be measured in the strain rate range from 833 s−1 to 1961 s−1 and the temperature conditions of 70 °C and 120 °C. It is worth noting that as a typical strain-rate hardening process, the maximum stress undergoes an initial ascending stage as the applied strain rate increases. Nevertheless, the hardening process is followed by a descending stage to indicate a softening process of maximum stress due to a further temperature increase during the rapid material deformation at higher strain rates. To gain a further insight into this maximum stress transition, the microstructure characterizations of the impacted solder specimens are carried out by a scanning electron microscope (SEM). It is found that the β-Sn phases and eutectic phases appear to experience refinement and then coarsen as the plastic strain rate continues to increase. A finite element (FE) model is created in the commercial nonlinear FE software ABAQUS/Explicit by considering all the experimental details. Since none of the existing material models in the material library is available for such a maximum stress transition with different ranges of strain rate, the mechanical properties of solder material are emphasized by proposing an improved Johnson-Cook model which can be readily utilized in the numerical evaluations of packaging structures under extremely high strain-rate conditions.

Wafer-level packaging solder joint reliability lifecycle prediction using SVR-based machine learning algorithm

Abstract The development of new electronic packaging structures often involves a design-on-simulation approach. However, simulation results can be subjective, and there can be variances in outcomes depending on who is conducting the simulation. To address this issue, packaging designers are now turning to machine learning to increase the accuracy and efficiency of the design process. This research study focuses on using support vector regression (SVR) techniques, such as single kernel, multiple kernels and a new SVR technique, to predict the reliability of the wafer-level packaging (WLP). By doing so, the study aims to provide designers with a reliable way to assess the reliability life cycle of their packaging designs. This research includes three steps: validating the WLP's reliability using finite element analysis (FEA) and experiment results, using the validated FEA result as input to obtain a predictive model through the SVR technique and the evaluating predictive model's performance. The results show that the predictive models developed using the SVR technique have stable performance on different testing data, which is consistent with the FEA results.

Unveiling the damage evolution of SAC305 during fatigue by entropy generation

Low-cycle thermal-mechanical fatigue loadings induce progressive and permanent degradation of mechanical properties of lead-free solder materials, and thus reduce the fatigue life of electronic devices. In this study, damage evolution and accumulation of Sn-3.0Ag-0.5Cu (SAC305), the most successfully commercialized lead-free solder material, was investigated by performing strain-controlled fatigue tests at different temperatures (288–373 K) and strain rates (0.001–0.004 s−1). Unlike existing empirical models, a fatigue damage model was proposed based on entropy generation related to the thermodynamic nature of fatigue damage. To be intrinsic to entropy generation, the proposed model was calibrated with the peak stress degradation at different temperatures and strain rates. Our findings showed that the damage parameter is closely related to temperature and strain rate and monotonically increases from 0 to 1 during the low-cycle fatigue loading, which unveiled the fact regarding the irreversibility of the internal entropy generation. For the first time, the damage evolution is found to be more associated with the applied strain rate than the temperature. By observations using an optical microscopy, the physical damage mechanism is elucidated for SAC305 solder by correlating microstructures and damage evolutions. The evolving dendritic β-Sn phase and the surrounding Sn-Ag-Cu ternary eutectic network also explained the effects of temperature and strain rate based on the energy dissipation. Our proposed damage model reconciled the damage accumulation of SAC305 solder subjected to the low-cycle fatigue loading, which is readily adopted to predict the fatigue life of the electronic packaging structures.

A new unified creep‐plasticity constitutive model coupled with damage for viscoplastic materials subjected to fatigue loading

AbstractA new unified creep‐plasticity (UCP) constitutive model coupled with damage is proposed for Sn–3.0Ag–0.5Cu (SAC305), one of the most successfully commercialized Pb‐free solders. By calibrating the proposed damage model based on entropy generation, the fatigue issues are elucidated for SAC305 solder at different temperatures and strain rates. After implementing a user‐defined material subroutine, finite element simulations with the proposed UCP‐damage model are capable of predicting the strength deterioration as the macroscopic response in terms of load‐deformation curves. More importantly, the UCP‐damage model reveals the damage accumulation and evolution of viscoplastic materials sensitive to fatigue deformation at different temperatures and strain rates. By comparing the predictions with and without damage, the equivalent plastic strains are obviously different when evaluating the thermal cycling fatigue life of electronic packaging structures, which confirms the significance of the UCP model reasonably coupled with the intrinsic description of damage by the concept of entropy generation.

Tuning high and low thermal expansion coefficients of Li2O–BaO–Al2O3–B2O3–SiO2/quartz LTCC composites by replacing quartz partly with α-Al2O3 or ZrO2

Low-temperature co-fired ceramics (LTCC) with adjustable coefficients of thermal expansion (CTE) based on Li 2 O–BaO–Al 2 O 3 –B 2 O 3 –SiO 2 /quartz LTCC composites (glass/ceramics) have been employed in electronic packaging to address the interface thermal mismatch problem caused by different thermal expansion coefficients. In the present study, sintering behavior, phase structure, and CTE of LTCC composites is controlled by replacing quartz partly with α-Al 2 O 3 or ZrO 2 . Accordingly, LTCC composites with the highest and lowest CTE values are achieved. The results show that the major phases of α-Al 2 O 3 substituted LTCC composites are hexacelsian, β-spodumene, and virgilite. Correspondingly, CTE values are in the range of 5.67–8.62 × 10 −6 /°C. Whereas, ZrO 2 substituted LTCC composites have exhibited increased CTE values to 12.27 to 13.2 × 10 −6 /°C with major phases of cristobalite, hexacelsian, and bazirite. Moreover, the negative effects of phase transformation of hexacelsian can be inhibited to a certain extent upon substitution of α-Al 2 O 3 up to 15 wt%. This work provides suitable methods for preparing LTCC composites with gradient CTE and resolving the thermal mismatch effects at different interfaces (e.g., chip/LTCC, metal electrode/LTCC) in electronic packaging structures.

Study of Electromigration-Induced Void Nucleation Problem Dominated by Bulk, Grain Boundary, and Interfacial Diffusion Based on an Improved Energy Approach

In this present article, an improved electromigration-induced void nucleation model is developed based on our previous work. The Gibbs free energy function of the electromigration-induced void nucleation process is reconstructed to well describe the electromigration-induced void nucleation process. The mass diffusion energy term in the Gibbs free energy function is obtained by the electromigration damage entropy model framework proposed by Basaran et al. The bulk diffusion, grain boundary diffusion, and interface diffusion effect during electromigration can be all considered. Thus, the applicability of the newly developed model is expanded and can be widely used not matter in the thin-film interconnects but also in the RDL and TSV interconnect structures in advanced electronic packaging. The electromigration-induced void initiation time and the critical void nucleation radius can be obtained analytically based on the present model. Several experiments conducted on these new structures are illustrated. It is shown that the theoretical results of the electromigration-induced void nucleation time can well match the experiments.

An Automatic Finite Element Method-Boundary Element Method Coupling Method for Elastic–Plastic Problems of Multiscale Structures in Electronic Packaging

Abstract We introduce a coupled finite and boundary element method for elastic-plastic analysis over multiscale electronic packaging structures. Based on the finite element-boundary element (FE-BE) coupling algorithm, an automatic implementation procedure for the coupling of the abaqus with a self-written elastic BE code is introduced for elastic problems. In the mixed finite element method (FEM)-boundary element method (BEM) model, the effective stiffness and effective forces at the interfacial boundary are evaluated by the self-written BE code. Then, the obtained effective stiffness and effective forces are assembled to the global FE formulations by using the user subroutine (UEL) in abaqus. Numerical simulation of structures with plastic deformation, stress concentration, etc. is carried out by using FEM theory. The boundary element method is used for linear elastic domains with large-scale structures. The proposed method offers several key improvements compared with current analysis methods available for multiscale electronic packaging structures. The benefits are: (i) the powerful pre- and postprocessing of abaqus; (ii) the higher accuracy of the solution; (iii) the computational cost and time can be reduced by using the scheme; and (iv) solving systems with infinite extension by using the BEM as a supplement. Furthermore, we demonstrate the ability of the proposed approach to handle multiscale structures in electronic packaging problems.

An isogeometric boundary element method for heat transfer problems of multiscale structures in electronic packaging with arbitrary heat sources

We present an isogeometric boundary element method (IGABEM) capable of studying heat transfer problems for multiscale structures in electronic packaging problems. This method offers a number of key improvements compared with current analysis methods available for electronic packaging problems. The method benefits from the accuracy, computational efficiency and CAD integration that have consistently been shown as features of the IGABEM. In addition, the current method can efficiently evaluate the nearly singular integrals caused by multiscale structures, owing to the use of a proposed hybrid integration scheme. By changing a tolerance, the scheme enables engineers to achieve any desired balance between accuracy and computational efficiency as may be appropriate to the situation. To study heat transfer problems with an arbitrary heat source, the radial integral method is used to transform the domain integral to an equivalent boundary integral. Numerical results are compared with available analytical solutions and finite element solutions and demonstrate the effectiveness of the proposed approach.

Effect of high-frequency PCB laminate on thermal cycling behavior of electronic packaging structures

PurposeAs the solution to improve fatigue life and mechanical reliability of packaging structure, the material selection in PCB stack-up and partitioning design on PCB to eliminate the electromagnetic interference by keeping all circuit functions separate are suggested to be optimized from the mechanical stress point of view.Design/methodology/approachThe present paper investigated the effect of RO4350B and RT5880 printed circuit board (PCB) laminates on fatigue life of the QFN (quad flat no-lead) packaging structure for high-frequency applications. During accelerated thermal cycling between −50 °C and 100 °C, the mismatched coefficients of thermal expansion (CTE) between packaging and PCB materials, initial PCB warping deformation and locally concentrated stress states significantly affected the fatigue life of the packaging structure. The intermetallics layer and mechanical strength of solder joints were examined to ensure the satisfactorily soldering quality prior to the thermal cycling process. The failure mechanism was investigated by the metallographic observations using a scanning electron microscope.FindingsTypical fatigue behavior was revealed by grain coarsening due to cyclic stress, while at critical locations of packaging structures, the crack propagations were confirmed to be accompanied with coarsened grains by dye penetration tests. It is confirmed that the cyclic stress induced fatigue deformation is dominant in the deformation history of both PCB laminates. Due to the greater CTE differences in the RT5880 PCB laminate with those of the packaging materials, the thermally induced strains among different layered materials were more mismatched and led to the initiation and propagation of fatigue cracks in solder joints subjected to more severe stress states.Originality/valueIn addition to the electrical insulation and thermal dissipation, electronic packaging structures play a key role in mechanical connections between IC chips and PCB.

Reverse Analysis of Surface Strain in Elasto-Plastic Materials by Nanoindentation

In this study, nanoindentation technology is utilized to investigate the in situ mechanical behavior of small-sized packaging materials. Rather than the ideal cases with unprestressed materials which have been intensively studies, this paper focuses on the effect of surface stress by prestressing the materials to be indented by a Berkovich indenter. The loading process until the maximum penetration depth is simulated by finite element (FE) models. With elastoplastic materials as described by a power-law model, extensive FE predictions are performed with the wide ranges of Young’s modulus, yield strength and hardening exponent with and without pre-strain. FE results show that with different prestress values, the applied load-penetration depth responses vary in a highly consistent manner. The residual indentation profiles are found to be closely related with the stress state due to the pre-strain values. On the basis of FE simulations, a dimensionless function is therefore derived and a reverse algorithm is proposed to estimate the constitutive parameters and also the surface stress of elastoplastic materials. With one of the most commercialized lead-free solder materials in electronic packaging structures, the proposed reverse algorithm is utilized to estimate the residual stress based on the nanoindentation response of solder samples with different annealing conditions.

Thermal analysis of electronic packaging structure using isogeometric boundary element method

The purpose of this paper is to carry out heat transfer analysis of integrated circuit (IC) packaging structures by the isogemoetric boundary element method (IGABEM). In service time, chips of electronic packaging structure produce lots of heat, which leads to resultant equations including domain integrals. In this work, the radial integration method is used to deal with domain integrals caused by the heat source. Since material properties of electronic packaging structure are piecewise continuous, the subregion isogemoetric boundary element method is introduced in the present IGABEM. In addition, the multi-scale property of structure leads to challenge of IGABEM analysis in electronic packaging problems. This largely results from the difficulty of integrating nearly singular integrals in an accurate and efficient manner. To deal with this problem, a hybrid nearly singular integration scheme, which delivers results of engineering accuracy in an optimal time is used in this work. Finally, a set of numerical examples demonstrate the ability of the present IGABEM to produce accurate temperature distributions.

Composites of Polymer Blends and Their Applications Using Natural Fibres: A Review

Study on new composite materials in engineering products with promising physical and mechanical properties has been considered as one of the fields of concern in recent decades. Strength, hardness and fatigue properties make engineering structural more flexible. They are extensively used in the aerospace industry, mechanical engineering applications and parts, electronic packaging, vehicle and aircraft structures, process industry equipment, as well as in biomedical equipment. Disposing of composite wastes however, are very difficult because of its structure and compositions. Hence, composite materials recycling has become one of the major measures of the future. This study seeks to analyse the present state of engineering plastics using natural fibers in their properties and manufacturing techniques. The effects of various chemical treatments on natural fibres’ mechanical and thermal properties have been studied in strengthening thermosetting and thermoplastics composites. The mix ratio of polymer waste used from the industry sector with natural fiber is expected to rise in the future, thus issues regarding recycling need to be tackled. It concluded that chemically treated natural fibre improved the adhesion between fibre surface and polymer matrix, which gradually increased the properties of natural fibres incorporated composites.

Methods to Reduce the Hierarchy of Interconnections in Electronic System

Abstract In the era of AI, 5G, big data, and autonomous driving, those applications all require a high bandwidth low latency data computing. Traditional electronic packaging structures are classified into many levels and each level are connected by solders or cables. These many levels of structures cause system performance degradation. Hence structure solutions of 2.5D, 2.1D, 2.3D and 2.0D with multi-chip packaging are needed for high performance computing system. Currently 2.5D is the HPC standard structure, however the cost and size limitation of 2.5D drive users to seek alternative solutions. The structure of 2.0D, 2.1D and 2.3D offer less solder and TXVs are emerging as contenders to fill the requirement of large substrate size and fine line requirements in the future. Among them 2.0D structure shows great potential. Three 2.0D test vehicles have been built to evaluate fine pitch assembly, reliability and structure enhancement. The results show 2.0D structure has great potential to be a HPC solution of the near future.