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To ensure the formation of high-quality solder joints, it is imperative to engage in surface preparation of the materials being joined, activate both the materials and solder, eliminate oxide films in the contact zone, facilitate interaction at the interfacial boundary, and induce crystallization of the liquid metal layer. This chapter delves into the processes involved in removing surface oxide films from solderable surfaces and discusses the pertinent equipment employed. Additionally, it highlights the potential efficacy of ultrasonic methods in oxide film removal through the introduction of elastic mechanical vibrations into the molten solder. Mathematical expressions are derived to elucidate the dynamics at the solder-surface interface, during the capillary penetration of solder into gaps and the diffusion process. The formation of a soldered joint with a specific structure results from the physicochemical interaction between the solder and the base metal. This joint typically encompasses a melting zone and diffusion zone at the solder and the base metal interface. The ultimate structure and composition of the solder joint depend on the nature of the interacting metals, their chemical affinity, and the soldering conditions, including time and temperature.

Electronic products are evolving towards miniaturization, high integration, and multi-function, which undoubtedly puts forward higher requirements for the reliability of solder joints in electronic packaging. Approximately 70% of failure in electronic devices originates during the packaging process, mostly due to the failure of solder joints. With the improvement of environmental protection awareness, lead-free solder joints have become a hot issue in recent years. This paper reviews the research progress on the reliability of lead-free solder joints and discusses the influence of temperature, vibration, tin whisker and electromigration on the reliability of solder joints. In addition, the measures to improve the reliability of solder joints are analyzed according to the problems of solder joints themselves, which provides a further theoretical basis for the study of the reliability of solder joints of electronic products in service.

During soldering and service, intermetallic compounds (IMCs) have an important impact on the performance and reliability of electronic products. A thin and continuous intermetallic layer facilitates the formation of reliable solder joints and improves the creep and fatigue resistance of solder joints. However, if the IMCs overgrow, the coarse IMC becomes brittle and tends to crack under stress, leading to a decrease in solder joint reliability. Based on the latest developments in the field of lead-free solders at home and abroad, this paper comprehensively reviews the interfacial reaction between SnAgCu Pb-free solders and different substrates and the growth behavior of IMCs and clarifies the growth mechanism of interfacial IMCs. The effects of the modification measures of lead-free solder on the IMCs and reliability of SnAgCu/substrate interface are analyzed, which provide a theoretical basis for the development and application of new lead-free solder.

Thermal fatigue is a common failure mode in electronic solder joints, yet the role of microstructure is incompletely understood. Here, we quantify the evolution of microstructure and damage in Sn-3Ag-0.5Cu joints throughout a ball grid array (BGA) package using EBSD mapping of localised subgrains, recrystallisation and heavily coarsened Ag 3 Sn. We then interpret the results with a multi-scale modelling approach that links from a continuum model at the package/board scale through to a crystal plasticity finite element model at the microstructure scale. We measure and explain the dependence of damage evolution on (i) the β-Sn crystal orientation(s) in single and multigrain joints, and (ii) the coefficient of thermal expansion (CTE) mismatch between tin grains in cyclic twinned multigrain joints. We further explore the relative importance of the solder microstructure versus the joint location in the array. The results provide a basis for designing optimum solder joint microstructures for thermal fatigue resistance. Thermal fatigue frequently leads to failure in electronic solder joints. Here, the authors measure and quantitatively explain how microstructure affects thermal fatigue in a ball grid array package and propose optimum microstructures for thermal fatigue resistance.

In this study, the Calculation of Phase Diagrams (CALPHAD) method was employed to predict the phase constitution of Sn1Ag.7Cu3Bi x In1.5Sb solder joints with different contents, which also guided the composition ratio of In in the system. Therefore, Sn1Ag.7Cu3Bi x In1.5Sb ( x = 4, 7, 12, 14, 17) solder joints were fabricated and investigated. According to experimental results, In addition could effectively lower the solidus and liquidus temperature supercooling degree of the alloy while increasing its melting range. In could substitute Sn atoms in the Cu6Sn5 phase to form a Cu 6 (Sn, In) 5 phase, and could induce the formation of Ag 2 (Sn, In), Ag 9 In 4 . When the In content exceeds 12 wt.%, the matrix phase γ-InSn 4 phase was formed. Based on the mechanical properties and post-mortem characterization, doping In could significantly ductile the solder joint with limited strength sacrifice, thanks to the increase in the phase volume fraction of the γ-InSn 4 phase. This study provides a viable method to relieve the brittleness of Sn1Ag.7Cu3Bi1.5Sb solder alloy while achieving a lower soldering temperature, which could serve as a guideline for future solder alloy design.

In the context of the ongoing development of multifunctional, portable, and thin and light portable electronic products, the study of the mechanical behavior of microelectronic package solder joints under drop impact loads has become a significant area of research in product reliability. This paper analyzes the displacement and stress of POP (Package-on-Package) package SAC305 (Sn0.3Ag0.5Cu) solder joints. The finite element simulation software was utilized to analyze the solder joints under drop impact load. The Input-G method was employed to apply the drop impact acceleration. The analysis revealed that the bottom corner solder joint 3 of the U2A component is the most hazardous solder joint in the package. The stress level of this solder joint determines the impact of the POP package during the drop impact process. A further key consideration when optimizing the design is the potential damage to the POP package during the drop shock process.

The Microstructural Hierarchy Descriptor (μSHD) is a systematic and extensible method for quantitative microstructural analysis. In this study, the μSHD method is used to investigate the microstructural evolution of solder joints in various external fields. The results show that the orientation in SAC305 joints is significantly larger on scales from J = 3 to 7 before aging, indicating pronounced network-like structures. However, this phenomenon disappears after isothermal aging, leading to a more uniform distribution of orientation across all scales. In SnAgInBi joints, both the scale and orientation features decrease on scales J < 7 but increase on scale J = 8 after thermal cycling, corresponding to grain coarsening. In Sn37Pb joints, features on orientations L = 1 and 8, which align with the direction of electron flow, show a significant increase after electromigration. Furthermore, features on scales J ≥ 5 increase, while changes on smaller scales are minimal. These findings demonstrate the usefulness of the μSHD method in capturing the nuanced microstructural changes of solder joints subjected to external fields, providing valuable and quantitative microstructural descriptors to establish linkages with the reliability of electronic assemblies.

In recent years, Moore’s law had a remarkable effect on predicting the development of semiconductor technology. As the size of devices shrinks to micro scale or nano scale, Intel’s newest 10-nm logic technology is scheduled to start product shipments before the end of 2017. Moore’s law will not die out, as the research scale reaches the atomic scale, “new devices” and new interconnection methods are urgently needed. In this paper, based on emerging interconnection requirement, the contribution to the advanced electronic packaging containing novel nano-materials, such as the carbon nanotubes, nanoparticles sintering, interconnection of nano-solder, nano-silver and surface plasma nano-welding are discussed. For the next 5–10 years, two new types of interconnect solutions are gaining attentions: solder joint alternatives and Cu electrode alternatives. The former uses new materials such as graphene, carbon nanotubes and nanowires to replace traditional solder joints. The latter uses optical media to replace the traditional Cu metal. In general, advanced materials will make more and more outstanding contributions in the development of electronic packaging in the next 10–20 years.

For the reason of reliability improvement of BGA solder, ANSYS is used to establish a BGA solder model that contains information such as size, material, grid, etc. The thermal stress of solder is selected as the optimization objective by the optimization parameters of solder height, solder radial direction, and spacing of solder. Response surface methodology is used to design 17 sets of different level parameters for simulation calculations, and a regression equation between solder joint stress and optimization parameters is established to obtain the parameter combination with the minimum stress of solder. The analysis results show that the corner solder far from the chip are critical solder joint for failure. The optimized solder joint parameters are as follows. The solder height is 0.5 mm, the solder radial is 0.6 mm, and the solder spacing is 1 mm. The optimized solder joint stress value is 30.818 MPa, which reduces the stress by 27.71% compared to before optimization, which achieved the reliability improvement of BGA solder.

The structural performance analysis and solder joint strength evaluation of spot-welded stainless-steel vehicles are associated with many working conditions, significant data, and repeated work. This will help researchers evaluate and improve calculation efficiency quickly. Taking the body structure of a spot-welded stainless-steel vehicle as the research object, this study conducted a finite element simulation analysis of its stiffness, static strength, mode, fatigue strength, and solder joint strength by the EN12663 standard. A rapid evaluation system for the solder joint strength was developed. The results showed that the performance of the vehicle body under various working conditions can meet the design requirements, and the evaluation results of the solder joint strength confirm the practicability and rapidity of the system, which can provide technical support for the subsequent improvement and optimization of vehicle body structures.