Matrix effect in soft metal-bonded samarium-cobalt (SmCo5) permanent magnets

This paper discusses the preparation of samarium-cobalt (SmCo₅) alloy powders by reduction-diffusion process. These powders were blended with equal weight percentages of soft metal/alloy powders, such as indium, tin and solder alloy (Pb-17Sn), to prepare bonded magnets. Important magnetic properties such as remanence, coercivity and energy product of these magnets were measured. Effect of matrix metal/alloy on the magnetic properties of processed magnets is outlined.     

A review of soft errors and the low α-solder bumping process in 3-D packaging technology

This study reviews soft errors in modern electronic assemblies, through silicon via (TSV), and low α-solder bumping techniques for 3-D microelectronic packaging. The TSV fabrication involves deep reactive ion-etching process of Si wafers to form vertical holes, which are further filled with copper and joined to solder bumps. The solder bumps in close proximity to Si die thus impose a serious threat of soft errors. These soft errors responsible for the malfunction of electronic systems have become a critical issue in miniaturized and high-density packaging, like 3-D packaging. Various low α-solder bumping techniques have been reported to minimize these errors in modern microelectronic devices. A low α-solder is one that has low levels of α-particle emission, as compared to the conventional solder. In addition, it improves the performance and reliability of the solder joints, prompting the need to adopt low α-solder for bumping in TSV packaging. Thus, this paper discusses the various aspects of TSV fabrication, functional layer deposition, Cu filling into TSV, and low α-solder bumping on TSV by solder ball reflow methods.     

铅基快淬钎料与电子焊膏焊点组织与力学性能的比较

在集成电路的一级封装中，常用高铅钎料，本文研究了使用高铅钎料时，镀金试样的焊点组织，并就新开发的快淬钎料与电子焊膏的焊点组织，力学性能做了对比研究，结果表明，快淬钎料焊点的组织均匀、细密，抗疲劳性能较好，在高可靠产品的生产中有较好的应用前景。     

Bond Strength of the Sn-Ti-Ⅹ Ternary Active Solders on Sialon Ceramic

The bond strength of the Sn based ternary active solders,Sn-5Ti with various contents of Ag,Cu,In,Ni or AI on sialon ceramic was investigated by the ceramic/ceramic joint joining.The bond strengthof Sn-STi (about 80 MPa) may increase to 90-100 MPa by small addition of Ag or Cu (about5-10%).A little Ni (about 1-3%) in the solder is slightly beneficial,but too more Ni (more than 5%)is harmful.Small addition of In is trivial,but too more In is detrimental.On the other hand,small addi-tion of AI in the active solder decreases greatly the bond strength of the solder,therefore it is veryharmful.In discussion,three suggestions for selection of the third element to increase the bondstrength of the soft solders on ceramic,i.e.with a high surface energy,benefiting to wetting on ce-ramic and strengthening the soft solder itself,have been made.     

Ductile fracture mechanism of low-temperature In-48Sn alloy joint under high strain rate loading

The failure behaviors of In-48Sn solder ball joints under various strain rate loadings were investigated with both experimental and finite element modeling study. The bonding force of In-48Sn solder on an Ni plated Cu pad increased with increasing shear speed, mainly due to the high strain-rate sensitivity of the solder alloy. In contrast to the cases of Sn-based Pb-free solder joints, the transition of the fracture mode from a ductile mode to a brittle mode was not observed in this solder joint system due to the soft nature of the In-48Sn alloy. This result is discussed in terms of the relationship between the strain-rate of the solder alloy, the work-hardening effect and the resulting stress concentration at the interfacial regions.     

延长自组织InAs／GaAs量子点发光波长的研究进展

在近几年的InAs／GaAs自组织量子点的研究中，如何荻得1．3～1．55μm。长波长量子点材料是一个很热门的课题。本文综述了各种延长自组织InAs／GaAs量子点发光波长的方法，并提出了实用化的最佳途径。     

Contact angle measurement of SAC 305 solder: numerical and experimental approach

The solder process comprises the ability of a melted alloy to flow or spread on a substrate for the formation of a metallic bond driven by the physical–chemical properties of the system. Thus, the study of wetting behaviour is an important step in the characterisation of solder alloys and requires the discussion of different parameters that affect the solder junctions. The main objective of this work is to use a CFD study to determine the influence of several parameters in the melting shape obtained with a solder, of the SAC 305 type and compare the numerical results with experimental data. The computational model was implemented in ANSYS Fluent^® and the simulations were carried out involving the melting of a material using the volume of fluid method to capture the solidification/melting interfaces based on an enthalpy-porosity approach. The results show that shape of the melted solder is greatly influenced by the contact angle and, to a smaller extent, by the surface tension. It was also concluded that it is possible to accurately predict the shape of the melted solder using computational fluid dynamic tools in complement to the experimental validation.     

Robust solder joint attachment of coaxial cable leads to piezoelectric ceramic electrodes

A technique was developed for the solder attachment of coaxial cable leads to silver-bearing thick-film electrodes on piezoelectric ceramics. Soldering the cable leads directly to the thick film caused bonds with low mechanical strength due to poor solder joint geometry. A barrier coating of 1.5 mum Cu/1.5 mum Ni/1.0 mum Sn deposited on the thick-film layer improved the strength of the solder joints by eliminating the adsorption of Ag from the thick film, which was responsible for the improper solder joint geometry. The procedure does not require special preparation of the electrode surface and is cost effective due to the use of nonprecious metal films and the batch processing capabilities of the electron beam deposition technique.     

机械合金化法制备Ag-Cu基中温合金钎料工艺研究

为研究机械合金化法制备Ag-Cu中温合金钎料的工艺过程,系统分析了球磨工艺参数对合金焊粉粒度及形貌演变的影响,确定了机械合金化制备球磨焊粉的优化工艺参数.采用X射线衍射仪(XRD)、扫描电镜(SEM)和差示扫描量热分析仪(DSC)等分析手段,对合金化过程中物相变化、微观结构及熔化特性进行了表征,并在此基础上进行了Ag-Cu基三元和四元焊粉机械合金化的研究.结果表明:Ag-Cu系合金焊粉经优化工艺(球料比20∶1,转速400 r/min,无水乙醇作为工艺控制剂,球磨40 h)球磨后,合金化完全,以过饱和固溶体为基体相;不同组元的添加对于焊粉尺寸形貌和相结构的影响不同.Ag-Cu-10Sn粉末在球磨40 h后生成了以亚稳态的过饱和固溶体Ag(Cu)为主要组成相的合金粉,其金相组织细小均匀,与不锈钢基板之间形成过渡层,有利于增加接头强度.这表明,通过控制球磨工艺和多组元的添加,可改变合金粉末的形貌和相结构,能得到过饱和固溶体为主要组成相的钎料合金,有利于改善钎料的性能.     

Microstructural damage analysis of SnAgCu solder joints and an assessment on indentation procedures

In solder joint reliability, solder/pad adjoining interface is crucial, the quality of which is determined by the metallization. In this paper, microstructural analyses of SnAgCu alloy and soldered joints are conducted in direct connection with the metallization. Solder balls, solder paste and cast SnAgCu are reflowed on Cu, Ni/Au and Cu/Ni(V)/Au. Substrate influence on bulk and interfacial metallurgy is examined and a correlation between interfacial microstructure and the corresponding damage paths is established. Damage localizes at the bonding interfaces with a strong influence of intermetallic layers and primary crystals. Crack propagation is studied with Cu and Ni/Au substrates and the cracking mechanism in principal directions is scrutinized. In BGA production, different reflow parameters are investigated, and an optimum bumping procedure is established. Nano-indentation is used for the mechanical characterization of the solder alloy. An assessment on indentation parameters for soft solders is conducted and the influence of Ag content on material properties of SnAgCu is presented.     

金相样品制备和分析中的技巧及方法

介绍了一般金相样品制备过程中样品高度对制样过程的影响，以及特殊的镶嵌技巧号；同时涉及了镧镍储氢材料样品制备的方法、技巧及效果，以及微差干涉技术在无铅钎料研究中的实际应用。     

A forward gradient time integration procedure for an internal variable constitutive model of Sn–Pb solder

A self-correcting forward gradient time integration procedure is formulated for the integration of a new unified visco-plastic constitutive model for an eutectic solder alloy using a tensorial internal state variable. The procedure has been implemented numerically into a commercial FE code through a user-material subroutine and is well suited to deal with numerically stiff constitutive equations. This is accomplished through an automatic subincrementation procedure controlled by a maximum allowed equivalent inelastic strain increment per time step. For illustration purposes, two examples are discussed: (i) uniaxial test simulations to reveal the optimum combination of the user-specified tolerance and the prescribed load step size to obtain a desired accuracy at a minimum cost, (ii) a large-scale three-dimensional analysis of an integrated circuit (IC) package's solder joint to show the capability of the proposed procedure to deal with thermomechanical loading.     

Implementation of the pin-in-paste process in a contract manufacturing environment

The pin-in-paste process was developed and validated for a contract manufacturing PCB assembly environment. A systematic approach was used to implement this process in a production environment. The sequence used for process development included solder paste volume calculations for through hole components (THCs), stencil aperture design for the pin-in-paste application, solder paste deposition through stencil printing, reflow profile development, inspection, and testing. A series of experiments were conducted to identify the 'process window' associated with each process step. The required volume of solder paste was computed using a set of empirical equations. The stencil printing process was 'optimized' using a 'design of experiments' based approach. Response surfaces were plotted and used to identify the 'optimal' print parameters. Thermal profiles were developed for reflow soldering the THCs in conjunction with the surface mount components (SMCs) in a single reflow pass. The assemblies were built using the 'optimized' process parameters. The assemblies were then inspected under an X-ray system to check for solder voiding. Electrical testing was then done to check for solder shorts and open connections. The shape of the solder joints was similar to a wave soldered joint, voiding was minimal, and there was no instance of solder shorts or an open connection. The solder joints were then cross-sectioned as a part of destructive testing. The cross sections showed the formation of good positive fillets (both top and bottom fillet), the solder paste had filled the plated through hole (PTH) completely, and voiding was minimal.     

The effect of adding Zn into the Sn–Ag–Cu solder on the intermetallic growth rate

Due to toxicity of lead in the commercial solder, lead-free solders were proposed. Among the potential lead-free solders, the Sn–Ag–Cu solders were considered as a potential replacement. To further improve the solder properties, a fourth element was added into the Sn–Ag–Cu solder. The present study investigates the effect of different weight percentage of Zn (up to 0.7 wt%) into the Sn-3.5Ag-1.0Cu solder on intermetallic and growth rate (k) after long time thermal aging. The solders were prepared using powder metallurgy method and X-ray diffraction analysis shows that there were Cu₆Sn₅, Cu₃Sn, CuZn and Ag₃Sn phases present after solder preparation. The solders were reacted with Cu substrate at 250 °C for 1 min and aged at 150 °C until 1,000 h. The morphology of the intermetallic was observed under scanning electron microscope and the elemental distribution was confirmed by energy dispersive X-ray. Intermetallic thickness and growth kinetic result show that the additions of 0.4 % zinc is sufficient in retarding the Cu₆Sn₅ and Cu₃Sn intermetallic growth.     

In situ nanoparticulate-reinforced lead-free Sn–Ag composite prepared by rapid solidification

Rapid solidification technology has been successfully adopted for the preparation of in-situ nanoparticulate-reinforced Sn–Ag composite solder. The applied rapid solidification process promotes nucleation and suppresses the growth of intermetallic compounds (IMCs) of Ag₃Sn during the eutectic solidification, yielding fine Ag₃Sn nanoparticulates with spherical morphology in the solidified solder structures. Those spherical, homogeneously-distributed nanoparticulates IMCs are benefit to improve the surface area per unit volume and obstruct the dislocation lines passing through the solder. Hence, this in-situ nanoparticulate-reinforced Sn–Ag composite exhibits higher microhardness.     

应用于SMT的无铅焊锡微粉制备方法研究展望

无铅焊锡微粉是一种可以满足SMT应用要求的环保材料。粉末的制备方法很多，但主要有4种，即化学还原法、电解法、机构粉碎法和雾化法等。通过对4种方法的对比可以知道，超音速气体雾化法制得的微粉粒度、颗粒形状和均匀性均能满足SMT的要求，所以可以应用超音速气体雾化法制备无铅焊锡微粉。     

Effect of bismuth–tin alloy particle diameter on bonding strength of copper nanoparticles/bismuth–tin solder hybrid joints

The effect of the diameter of Bi–Sn alloy particles on the bonding strength of hybrid joints formed between SiC chips and direct-bonded copper (DBC) plates using a Cu nanoparticles/Bi–Sn solder was studied. The bonding strength was the highest at 40 MPa for a Bi–Sn alloy particle diameter of 10 µm. Further, the bonding strength was dependent on the area of the bonding layer adhering to the SiC-side fracture surface, as determined by the die-shear test. Ni, which was deposited on the SiC chips and DBC plates before the bonding process, remained near the interfacial area of the bonding layer in the joints formed using the 5 µm particles. In contrast, Ni diffused all over the bonding area, with the exception of the interfacial area where Cu–Sn compounds were formed, in the joints produced using the larger alloy particles. The distribution of Sn in the bonding layer became more uniform and the segregation of Bi at the interface became more pronounced as the particle size was reduced. Further, with an increase in the particle size, the Ag layers deposited on the surfaces of the SiC chips and DBC plates diffused into the bonding layer after the first firing step at 473 K, which was performed before the secondary firing step at 623 K. These results imply that the diameter of the Bi–Sn solder particles in hybrid joints affects the interfacial structure, as it governs the wetting behavior of the Bi–Sn solder and hence has a determining effect on the bonding strength.     

Nanoindentation for measuring individual phase mechanical properties of lead free solder alloy

The elimination of lead from electronics due to its detrimental effects to environment and health is pushing component manufacturers to consider lead free solder alloys as the substitute. Application of such alloys requires a better understanding of their mechanical behavior at small volume size and at elevated temperatures. Such information is still lacking for both solder joints and bulk materials. In this study, nanoindentation technique was used to investigate the mechanical properties, namely the hardness and Young’s modulus, of the constituent phases in a near eutectic ternary SAC387 lead free solder alloy. The indentation-induced piling-up of the soft Sn phase was accounted for in the nanoindentation mechanical property calculations using a semi-ellipse method. The modified results agreed well with previous studies on similar alloys. Also, finite element simulation was used to estimate the effect of the complicated network between the eutectic Sn and the intermetallic phases on the mechanical properties acquired, which showed that the tested modulus of the intermetallic phase in the eutectic area exhibited considerable reduction. Vickers tests were also carried out at elevated temperatures, and the hardness of constituent phases dropped 35% from 25 °C to 85 °C.     

A study of Ag additive methods by comparing mechanical properties between Sn57.6Bi0.4Ag and 0.4 wt% nano-Ag-doped Sn58Bi BGA solder joints

Sn–Bi solder was proposed as one of the most promising substitutes for lead solder due to its lower melting temperature, good wettability, good yield strength and cost efficiency. With Ag elements added, the mechanical properties of Sn–Bi solder were improved obviously. There are two ways that are commonly used to add the reinforced particles into the solder. The first way (Way I) is to blend the reinforced particles with solder powders together, and then followed by pressure forming, sintering, cooling, crystallization and serious machining methods under inert atmosphere to make the solder paste. Another way (Way II) is to directly add the reinforced nano or micro particles into the solder paste by sufficient mechanical-stirring. In this research we would like to get fully understanding on the effects of these two ways of Ag addition on the mechanical properties of Sn–Bi–Ag solder joints during aging. Sn57.6Bi0.4Ag solder stands for the Way I and the doped Sn58Bi + 0.4Ag solder stands for the Way II. These two kinds of joints were compared via micromorphology observation, thermal failure analyses as well as balls shear strength measurement after different aging time (under 100 °C, from 0 to 800 h). The mechanical properties of Sn57.6Bi0.4Ag and the doped Sn58Bi + 0.4Ag solder joints during aging were shown to be associated with the changes of micromorphology, the dissolution of IMCs, as well as the flatness of the joints’ interface. Before long-time aging, the doped Sn58Bi + 0.4Ag solder joints showed better mechanical performance than Sn57.6Bi0.4Ag solder joints. During aging, Sn56.7Bi0.4Ag solder joints had better performance in preventing the dissolution of Ni–Sn IMCs into the solder side, having smoother interfaces, comparing with Sn58Bi + 0.4Ag solder joints. The degenerated phenomenon of Ag nanoparticle reinforcement seriously happened in the doped Sn58Bi + 0.4Ag solder joints. After longtime aging, Sn57.6Bi0.4Ag solder joints had better mechanical properties than the doped Sn58Bi + 0.4Ag solder joints.     

Tin whiskers growth of SnAgIn solder on Kovar substrate with Au/Ni plating

In this research, the interactions of SnInAg solder on Kovar leadframes (Fe29Ni17Co) with Au/Ni UMB was studied, to reveal the whiskers growth mechanism. Samples were prepared by reflow process and aging, with SnInAg solder paste on the substrate. Scanning electron microscope was used to observe the morphology and the cross-sectioned structure of the whiskers. Focused ion-beam was used for the preparation of the transmission electron microscope (TEM) samples, and energy dispersive X-ray and TEM were then used to distinguish the different intermetallic compound (IMC) phases. It was found that, a special solder thickness range would be needed for the growth of whiskers. The root cause of this strip whiskers growth region was studied. It is worthy to mention that, the Sn–Cu reactions, which was reported by many former researches, was not the main source of the compressive stress here. It was found that the Au–Sn reactions, the IMCs transformation during the aging process, and the oxidation layer growth were dominating the whiskers growth. Effects of cracks on the whiskers growth were carefully observed and discussed, and it was found that cracks under a certain width could exempt the breaking of the oxidation layer at the solder surface, thus help the whiskers growth. On the other hand, wide cracks might accommodate the deformation of the solder layer and prohibit the whiskers from being erupted out.