Effects of Ga,Al, Ag,and Ce multi-additions on the wetting characteristics of Sn-9Zn lead-free solder

An orthogonal method was used to evaluate the effects of Ga, Al, Ag, and Ce multi-additions on the wetting characteristics of Sn-9Zn lead-free solders by wetting balance method. The results show that the optimal loading of Ga, Al, Ag, and Ce was 0.2 wt.%, 0.002 wt.%, 0.25 wt.%, and 0.15 wt.%, respectively. Intermetallic compounds (IMCs) formed at the interface between Sn-9Zn-0.2Ga-0.002Al-0.25Ag-0.15Ce solder and Cu substrate were investigated by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis. The SEM images illustrate that the IMCs can be divided into two portions from the substrate side to the solder side: a planar Cu₅Zn₈ layer and an additional continuous scallop-like AgZn₃ layer. The EDS analysis also shows that Ga segregates in the solder abutting upon the interface. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) of the surface components of Sn-9Zn-0.2Ga-0.002Al-0.25Ag-0.15Ce solder indicate that Al aggregates at the surface in the form of Al₂O₃ protective film, which prevents the further oxidation of the solder surface. On the other hand, Ce aggregates at the subsurface, which may reduce the surface tension of the solder and improve the wettability in consequence.     

Interfacial reactions between Sn–8Zn–3Bi–xAg lead-free solders and Cu substrate

The formation and the growth of the intermetallic compounds (IMCs) at the interface between the Sn–8Zn–3Bi–xAg (x = 0, 0.5, and 1 wt.%) lead-free solder alloys and Cu substrate soldered at 250 °C for different durations from 5 to 60 min were investigated. It was found that Cu₅Zn₈ and CuZn₅ formed at Sn–8Zn–3Bi/Cu interface, and Cu₅Zn₈ and AgZn₃ formed at the solder/Cu interface when the solder was added with Ag. The thickness of IMC layers in different solder/Cu systems increased with increasing the soldering time. And the growth of the IMCs was found to be mainly controlled by a diffusion mechanism. Additionally, the growth of the IMC layers decreased with increasing content of Ag in the soldering process.     

Effect of rare earth metal Ce addition to Sn-Ag solder on interfacial reactions with Cu substrate

The effect of adding a small amount of rare earth cerium (Ce) element to low Ag containing Sn-1wt%Ag Pb-free solder on its interfacial reactions with Cu substrate was investigated. The growth of intermetallic compounds (IMCs) between three Sn-1Ag-xCe solders with different Ce contents and a Cu substrate was studied and the results were compared to those obtained for the Ce-free Sn-1Ag/Cu systems. In the solid-state reactions of the Sn-1Ag(-xCe)/Cu solder joints, the two IMC layers, Cu₆Sn₅ and Cu₃Sn, grew as aging time increased. Compared to the Sn-1Ag/Cu joint, the growth of the Cu₆Sn₅ and Cu₃Sn layers was depressed for the Ce-containing Sn-1Ag-xCe/Cu joint. The addition of Ce to the Sn-Ag solder reduced the growth of the interfacial Cu-Sn IMCs and prevented the IMCs from spalling from the interface. The evenly-distributed Ce elements in the solder region blocked the diffusion of Sn atoms to the interface and retarded the growth of the interfacial IMC layer.     

Interfacial reactions of Sn–Zn–Ag–Cu alloy on soldered Al/Cu and Al/Al joints

This work shows the effect on the soldering process of the addition of Ag and Cu to Sn–Zn alloys. Soldering of Al/Cu and Al/Al joints was performed for a time of 3?min, at a temperature of 250°C, with the use of flux. Aging was carried out at 170°C for Al/Cu and Al/Al joints for 1 and 10 days. During the aging process, intermetallic layers grew at the interface of the Al/Cu joint at the Cu substrate. Intermetallic layers were not observed during wetting of Al/Al joints. On the contrary, dissolution of the Al substrate and migration of Al-rich particles into the bulk of the solder were observed. The experiment was designed to demonstrate the effect of Ag and Cu addition on the dissolution of Al substrate during the soldering and aging processes. In the solder alloys, small precipitates of AgZn₃ and Cu₅Zn₈ were observed.     

The Inhibition of Tin Whiskers on the Surface of Sn-8Zn-3Bi-0.5Ce Solders

Through the refinement of the (Ce, Zn)Sn₃ intermetallic phase, the formation of tin whiskers, previously observed on the surface of a Sn-3Ag-0.5Cu-0.5Ce solder, was prevented in a Sn-9Zn-0.5Ce alloy. However, whisker growth can still occur on the surface of Sn-8Zn-3Bi-0.5Ce solder after air storage at room temperature and at 150 °C due to the formation of large (Ce, Zn)Sn₃ intermetallic clusters. Further experiments showed that decreasing the Bi-content in this Sn-8Zn-0.5Ce alloy to 1 and 2 wt.% can recover the beneficial effects of Zn additions on the refinement of the (Ce, Zn)Sn₃ phase and obviously reduce the appearance of tin whiskers. In addition, alloying the Sn-8Zn-3Bi-0.5Ce solder with 0.5 wt.% Ge, which increases the oxidation resistance of the (Ce, Zn)Sn₃ intermetallic clusters, can also effectively inhibit tin whisker growth.     

Understanding the Influence of Copper Nanoparticles on Thermal Characteristics and Microstructural Development of a Tin-Silver Solder

This paper presents and discusses issues relevant to solidification of a chosen lead-free solder, the eutectic Sn-3.5%Ag, and its composite counterparts. Direct temperature recordings for the no-clean solder paste during the simulated reflow process revealed a significant amount of undercooling to occur prior to the initiation of solidification of the eutectic Sn-3.5%Ag solder, which is 6.5 °C, and for the composite counterparts, it is dependent on the percentage of copper nanopowder. Temperature recordings revealed the same temperature level of 221 °C for both melting (from solid to liquid) and final solidification (after recalescence) of the Sn-3.5%Ag solder. Addition of copper nanoparticles was observed to have no appreciable influence on melting temperature of the composite solder. However, it does influence solidification of the composite solder. The addition of 0.5 wt.% copper nanoparticles lowered the solidification temperature to 219.5 °C, while addition of 1.0 wt.% copper nanoparticles lowered the solidification temperature to 217.5 °C, which is close to the melting point of the ternary eutectic Sn-Ag-Cu solder alloy, Sn-3.7Ag-0.9Cu. This indicates the copper nanoparticles are completely dissolved in the eutectic Sn-3.5%Ag solder and precipitate as the Cu₆Sn₅, which reinforces the eutectic solder. Optical microscopy observations revealed the addition of 1.0 wt.% of copper nanoparticles to the Sn-3.5%Ag solder results in the formation and presence of the intermetallic compound Cu₆Sn_5. These particles are polygonal in morphology and dispersed randomly through the solder matrix. Addition of microsized copper particles cannot completely dissolve in the eutectic solder and projects a sunflower morphology with the solid copper particle surrounded by the Cu₆Sn₅ intermetallic compound coupled with residual porosity present in the solder sample. Microhardness measurements revealed the addition of copper nanopowder to the eutectic Sn-3.5%Ag solder resulted in higher hardness.     

Effects of Al, Ga, and Ag on the anti-oxidation and wetting reactions of Sn-9Zn-X solders

The effects of Ca, Al, and Ag on the anti-oxidation of Sn-9Zn-X solders and the interface reactions between the solders and Cu substrate were investigated by Auger electron spectroscopy (AES) and scanning electron microscope (SEM) analysis, respectively. The mechanism of improving the wettability of Sn-g Zn lead-flee solder by adding Ca, Al, and Ag was also revealed. The AES analysis indicated that Al and Ca might enrich on the molten solder surface which resulted in improving the anti-oxidation of Sn-gZn-O. O05Al and Sn-gZn-O. 3C, a alloys. The addition of Ca reduced the apparent activation energy and promoted the interface reaction. With the addition of 0.3 wt. % Ag, some scallop-like intermetallic compounds (IMCs) formed at the interface, according to the energy dispersive spectroscopy (EDS) analysis, these scallop-like IMCs might be the mixture of Ag-Zn and Cu-Sn compounds.     

Intermetallic compound growth suppression at high temperature in SAC solders with Zn addition on Cu and Ni-P substrates

The effect of adding 0.5-1.5 wt.% Zn to Sn-3.8Ag-0.7Cu (SAC) solder alloy during reflow and solid state ageing has been investigated. In particular, the role of the Zn addition in suppressing interfacial Intermetallic Compound (IMC) growth on Cu and Ni-P substrates has been determined. Solder-substrate couples were aged at 150 °C and 185 °C for 1000 h. In the case of 0.5-1.0 wt.% Zn on Cu substrate, Cu₃Sn IMC was significantly suppressed and the morphology of Cu₆Sn₅ grains was changed, leading to suppressed Cu₆Sn₅ growth. In the SAC-1.5Zn/Cu substrate system a Cu₅Zn₈ IMC layer nucleated at the interface followed by massive spalling of the layer into the solder, forming a barrier layer limiting Cu₆Sn₅ growth. On Ni-P substrates the (Cu,Ni)₆Sn₅ IMC growth rate was suppressed, the lowest growth rate being found in the SAC-1.5Zn/Ni-P system. In all cases the added Zn segregated to the interfacial IMCs so that Cu₆Sn₅ became (Cu,Zn)₆Sn₅ and (Cu,Ni)₆Sn₅ became (Ni,Cu,Zn)₆Sn₅. The effect of Zn concentration on undercooling, wetting angles and IMC composition changes during ageing are also tabulated, and a method of incorporating Zn into the solder during reflow without compromising solder paste reflow described.     

Investigation of small Sn–3.5Ag–0.5Cu additions on the microstructure and properties of Sn–8Zn–3Bi solder on Au/Ni/Cu pads

The formation of intermetallic compounds and the shear strength of Sn–Zn–Bi solder alloys with various (0, 1, 3, 5 and 7 wt%) weight percentages of Sn–Ag–Cu were investigated on Au/Ni metallized Cu pads depending on the number of reflow cycles. In Sn–Zn–Bi solder joints, scallop-shaped AuZn₃ intermetallic compound (IMC) particles were found at the interfaces and in the solder ball regions, fine Bi- and needle-shaped Zn-rich phase were observed in the Sn matrix. After Sn–Ag–Cu additions, an additional Ag–Zn intermetallic compound layer was adhered to the top surface of the AuZn₃ layer at the interface and fine spherical-shaped AgZn₃ intermetallic compound particles were detected in the solder ball regions together with Bi- and Zn-rich phase volumes. After the addition of Sn–Ag–Cu, the shear strength of Sn–Zn–Bi solder joints increased due to the formation of the fine AgZn₃ intermetallic compound particles. The shear strengths of Sn–Zn–Bi and Sn–Zn–Bi/7 wt% Sn–Ag–Cu solder joints after one reflow cycle were about 44.5 and 53.1 MPa, respectively and their shear strengths after eight reflow cycles were about 43.4 and 51.6 MPa, respectively.     

Intermetallic Compounds Formed in Sn-20In-2.8Ag Solder BGA Packages with Ag/Cu Pads

The interfacial reactions in a Sn-20In-2.8Ag solder ball grid array (BGA) package with immersion Ag surface finish are investigated. After reflow, the Ag thin film dissolves quickly into the solder matrix, and scallop-shaped intermetallic layers, with compositions of (Cu_0.98Ag_0.02)₆(In_0.59Sn_0.41)₅, appear at the interfaces between Sn-20In-2.8Ag solder ball and Cu pad. No evident growth of the (Cu_0.98Ag_0.02)₆(Sn_0.59In_0.41)₅ intermetallic compounds was observed after prolonged aging at 100 °C. However, the growth accelerated at 150 °C, with more intermetallic scallops floating into the solder matrix. The intermetallic thickness versus the square root of reaction time (t ^1/2) shows a linear relation, indicating that the growth of intermetallic compounds is diffusion-controlled. Ball shear tests show that the strength of Sn-20In-2.8Ag solder joints after reflow is 4.4 N, which increases to 5.18 N and 5.14 N after aging at 100 and 150 °C, respectively.     

Sn-9Zn钎料与内加Cu质点和Cu基体界面生长行为

在Sn-9Zn无铅钎料中加入Cu金属质点,研究在长时间钎焊条件下钎料/Cu质点、钎料/Cu基体界面金属间化合物（IMCs）的生长行为。结果表明：在钎料/Cu质点和钎料/Cu基体界面处都生成Cu-Zn相（IMCs）,其组成为Cu5Zn8＋CuZn或Cu5Zn8,而且钎料/质点界面处IMCs的生长速度明显快于钎料/基体处;同时发现,Cu质点的加入大大减小了钎料/Cu基体界面IMCs的厚度。由于Cu质点原位生成Cu-Zn IMCs,消耗了焊点中的Zn,因此Sn-9Zn/Cu接头的可靠性得以提高。     

Reliability studies of Sn–9Zn/Cu solder joints with aging treatment

Sn–9Zn (in wt.%) solder ball was bonded to Cu pad, and the effect of aging on shear reliability was investigated. After reflow, the intermetallic compound (IMC) phase formed at the interface was Cu₅Zn₈, and the as-reflowed Sn–9Zn/Cu joint had sufficient shear strength. In the isothermal aging test, only Cu₅Zn₈ IMC was observed in the samples aged at temperatures between 70 and 120 °C. On the other hand, after aging at 150 °C for 250 h, Cu₆Sn₅ phase was observed at the interface between the interfacial Cu₅Zn₈ IMC layer and the Cu substrate. And, the layer-type Cu₅Zn₈ IMC layer was disrupted locally at the interface. In the ball shear test conducted after aging treatment, the shear strength significantly decreased after aging at all temperatures for initial 100 h, and then remained constant by further prolonged aging. The fracture mainly occurred at the interface between the solder and Cu₅Zn₈ IMC layer. The aged Sn–9Zn/Cu solder joint had an inferior joint reliability.     

Effect of bismuth on the growth kinetics of intermetallic compounds in Sn-3.5Ag solder joints: A growth kinetic model

The effect on the growth kinetics of the intermetallic compounds (IMCs) in solder/Cu joints, caused by adding Bi to eutectic Sn-3.5Ag solder alloy, was examined at the aging temperatures of 150°C and 180°C. The Cu₆Sn₅ layer growth was significantly enhanced, but the Cu₃Sn layer growth was slightly retarded by the addition of Bi, resulting in significant growth enhancement of the total (Cu₆Sn₅+Cu₃Sn) IMC layer with increasing Bi addition. The IMC layer growth in the Bi-containing solder joints was accompanied by the accumulation of Bi ahead of the Cu₆Sn₅ layer that resulted in the formation of a liquid layer at the Cu₆Sn₅/solder interface. A kinetic model was developed for the planar growth of the Cu₆Sn₅ and Cu₃Sn layers in the solder joints, accounting for the existence of interfacial reaction barriers. Predictions from the kinetic model showed that the experimental results could be well explained by the hypothesis that the formation of a Bi-rich liquid layer at the Cu₆Sn₅/solder interface reduces the interfacial reaction barrier at the interface.     

(Sn1-xZnx)57(In0.78Bi0.22)43低熔点无铅焊料的微观结构表征(英文)

为了寻求一种应用于三维集成电路低温焊接的无铅焊料，基于多组元混合的概念设计并表征(Sn_1-xZn_x)₅₇-(In_0.78Bi_0.22)₄₃ (x=0.10,0.15,0.20，摩尔分数，%)四元合金。采用扫描电子显微镜、X射线衍射仪和差示扫描量热仪研究合金的显微组织、热性能和润湿性。结果表明，合金由金属间化合物BiIn₂、In_0.2Sn_0.8和富Zn固溶体组成。随着Zn添加量的增加，BiIn₂和富Zn相的体积分数增加。合金的熔点低至70℃，源自低熔点金属间化合物In_0.2Sn_0.8和BiIn₂的形成；合金具有良好的润湿性，润湿角约为40°。在合金和Cu板的界面结合处形成一种薄而坚韧的Cu₅Zn₈层，提高焊点可靠性。研究表明，通过多组元混合概念设计合金可以有效提高...     

稀土Pr对低银Sn-0.3Ag-0.7Cu-0.5Ga钎料蠕变行为影响的研究

为进一步促进电子封装用低银无铅钎料的发展,本文采用纳米压痕法研究了新型含Pr低银Sn-0.3Ag-0.7Cu-0.5Ga (SAC-Ga)钎料显微组织与蠕变性能之间的关系。结果表明,SAC-Ga、SAC-Ga-0.06Pr、SAC-Ga-0.5Pr三种钎料的蠕变位移分别为1717 nm、1144 nm、1472 nm;稀土Pr可通过细化Cu₆Sn₅金属间化合物并促使其均匀分布从而明显提高SAC-Ga钎料的蠕变强度;与SAC-Ga-0.06Pr钎料相比,SAC-Ga-0.5Pr由于过量稀土Pr的表面氧化而导致其蠕变强度有所下降。此外,本文采用Dorn模型研究了含Pr的SAC-Ga钎料的室温蠕变行为并计算了对应的钎料蠕变应力指数n;阐明了Pr对SAC-Ga钎料蠕变强度的强化机理,即当位错遇到细小且均匀分布的Cu₆Sn₅ 金属间化合物时,位错移动只能采用绕过机制,从而提高了含Pr低银钎料的抗蠕变性能。     

微量锌对Sn-3.5Ag无铅钎料/铜界面金属间化合物生长的抑制

在钎焊和时效条件下,研究了Sn-3.5Ag无铅钎料中添加0.2%的Zn元素后对钎料/铜界面组织形貌的影响.结果表明,钎焊条件下,将0.2%的Zn元素加入到Sn-3.5Ag钎料中对Cu-Sn间的金属间化合物及其扇贝形形状不产生影响.时效处理后,0.2%Zn元素的加入对界面IMC层的厚度、组成及形态都有影响.在Sn-3.5...     

Interfacial Reactions and Bonding Strength of Sn-xAg-0.5Cu/Ni BGA Solder Joints

The present study details the microstructure evolution of the interfacial intermetallic compounds (IMCs) layer formed between the Sn-xAg-0.5Cu (x = 1, 3, and 4 wt.%) solder balls and electroless Ni-P layer, and their bond strength variation during aging. The interfacial IMCs layer in the as-reflowed specimens was only (Cu,Ni)₆Sn₅ for Sn-xAg-0.5Cu solders. The (Ni,Cu)₃Sn₄ IMCs layer formed when Sn-4Ag-0.5Cu and Sn-3Ag-0.5Cu solders were used as aging time increased. However, only (Cu,Ni)₆Sn₅ IMCs formed in Sn-1Ag-0.5Cu solders, when the aging time was extended beyond 1500 h. Two factors are expected to influence bond strength and fracture modes. One of the factors is that the interfacial (Ni,Cu)₃Sn₄ IMCs formed at the interface and the fact that fracture occurs along the interface. The other factor is Ag₃Sn IMCs coarsening in the solder matrix, and fracture reveals the ductility of the solder balls. The above analysis indicates that during aging, the formation of interfacial (Ni,Cu)₃Sn₄ IMCs layers strongly influences the pull strength and the fracture behavior of a solder joint. This fact demonstrates that interfacial layers are key to understanding the changes in bonding strength. Additionally, comparison of the bond strength with various Sn-Ag-Cu lead-free solders for various Ag contents show that the Sn-1Ag-0.5Cu solder joint is not sensitive to extended aging time.     

Ag,Al,Ga对Sn-9Zn无铅钎料润湿性能的影响

采用润湿平衡法测试了Sn-9Zn-X(X为Ag,Al,Ga)无铅钎料分别配合ZnCl2-NH4Cl钎剂和免清洗助焊剂,在空气和氮气保护的两种条件下的润湿性能,分析研究了合金元素Ag,Al,Ga的添加量对Sn-9Zn-X无铅钎料润湿性的影响规律.结果表明,合金元素Ag,Al,Ga在Sn-9Zn中的最佳添加量(质量分数)分别为0.3%,0.005%～0.02%,0.5%.采用氮气保护可以显著改善Sn-9Zn-X无铅钎料的润湿性,而Sn-9Zn-X无铅钎料配合ZnCl2-NH4Cl钎剂时具有较好的润湿性,甚至优于Sn-3.5Ag-0.5Cu在相同条件下的润湿性.这一研究结果表明,通过研发适合于Sn-Zn系无铅钎料的高性能助焊剂,从而改善Sn-Zn系钎料的润湿性能是完全可行的.     

Reaction diffusions of Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> and Cu<Subscript>3</Subscript>Sn intermetallic compound in the couple of Sn-3.5Ag eutectic solder and copper substrate

The growth kinetics of intermetallic compound layers formed between Sn-3.5Ag solder and Cu substrate were investigated as a consequence of solid-state isothermal aging. Isothermal aging was carried out in a temperature range between 70°C and 200°C for 0 to 60 days. A quantitative analysis of the intermetallic compound layer thickness as a function of time and temperature was performed. The diffusion couples showed a composite intermetallic layer comprised of Cu₆Sn₅ and Cu₃Sn. The growth of intermetallic compounds followed diffusion-controlled kinetics and the layer thickness reached only 9 μm after 60 day of aging at 150°C. The apparent activation energies were calculated for the growth of the total intermetallic compound (Cu₆Sn₅+Cu₃Sn); Cu₆Sn₅ and Cu₃Sn intermetallic are 65.4, 55.4 and 75.7 kJ/mol, respectively.     

Effects of rapid solidification on the microstructure and microhardness of a lead-free Sn-3.5Ag solder

A lead-free Sn-3.5Ag solder was prepared by rapid solidification technology. The high solidification rate, obtained by rapid cooling, promotes nucleation, and suppresses the growth of Ag3Sn intermetallic compounds （IMCs） in Ag-rich zone, yielding fine Ag3Sn nanoparticulates with spherical morphology in the matrix of the solder. The large amount of tough homogeneously-dispersed IMCs helps to improve the surface area per unit volume and obstructs the dislocation lines passing through the solder, which fits with the dispersion-strengthening theory. Hence, the rapidly-solidified Sn-3.5Ag solder exhibits a higher rnicrohardness when compared with a slowly-solidified Sn-3.5Ag solder.