The microstructure of eutectic Au-Sn solder bumps on Cu/electroless Ni/Au

In this work we studied the initial microstructure and microstructural evolution of eutectic Au-Sn solder bumps on Cu/electroless Ni/Au. The solder bumps were 150–160 m in diameter and 45–50 m tall, reflowed on Cu/electroless Ni/Au, and then aged at 200°C for up to 365 days. In addition, Au-Ni-Sn-alloys were made and analyzed to help identify the phases that appear at the interface during aging. The detailed interfacial microstructure was observed using a transmission electron microscope (TEM). The results show that the introduction of Au from the substrate produces large islands of-phase in the bulk microstructure during reflow. Two Au-Ni-Sn compounds are formed at the solder/substrate interface and grow slowly during aging. The maximum solubility of Ni in the—phase was measured to be about 1 at.% at 200°C, while Ni in the-phase is more than 20 at.%. The electroless Ni layer is made of several sublayers with slightly different compositions and microstructures. There is, in addition, an amorphous interaction layer at the solder/electroless Ni interface.     

Reliability of In-48Sn solder/Au/Ni/Cu BGA packages during reflow process

The interfacial reactions and shear properties of In-48wt.%Sn/Au/Ni/Cu solder joints were investigated in terms of reflow conditions, i.e., reflow temperature and duration time. The thickness of an AuIn₂ intermetallic compound (IMC) layer, formed at the solder/substrate interface, slightly increased with the duration time. The spalling of the AuIn₂ intermetallics in the solder led to the formation of a Ni₃(Sn,In)₄ IMC layer between the solder and exposed Ni layer. The longer duration time resulted in the spalling and grain growth of Ni₃(Sn,In)₄ intermetallics. The higher reflow temperature accelerated the interfacial reactions between the solder and substrate. From the ball shear test results, the formation and growth of a continuous plate-shaped AuIn₂ IMC layer increased the shear force of the solder joints, whereas the spalling and grain growth of cubic-shaped AuIn₂ intermetallics significantly decreased the shear force. The formation and spalling of cubic-shaped Ni₃(Sn,In)₄ intermetallics increased the shear force, whereas the spalling and grain growth of polyhedron-shaped Ni₃(Sn,In)₄ intermetallics decreased the shear force. The crack propagated at the Au-rich/AuIn₂/solder interface in the initial reflow stage, then toward the AuIn₂ intermetallics dispersed in the solder matrix, and finally along the Ni₃(Sn,In)₄ intermetallics spalling off in the solder.     

Characterization of the growth of intermetallic interfacial layers of Sn-Ag and Sn-Pb eutectic solders and their composite solders on Cu substrate during isothermal long-term aging

Single shear lap joints were made with four different solders, Sn-Pb and Sn-Ag eutectic solders, and their composites containing about 20 vol.% in-situ Cu6Sn5 intermetallic phases about 3–8 micrometers in diameter. Two sets of experiments were performed: In the first set, all of the above four solder joints were aged at 150°C for periods ranging to 5000 h and the intermetallic growth was monitored periodically. In the second set, each of the above four solder joints was aged at five different temperatures for 4000 h. The interfacial layers between solders and the Cu substrate were examined using optical and scanning electron microscopy. The growth kinetics of intermetallic interfacial layers formed between solder and Cu substrate was characterized. The effect of in-situ Cu₆Sn₅ intermetallic phases on the growth rate is discussed. The growth rate of the intermetallic layers in the eutectic Sn-Pb composite was slower for the first 150 h as compared to the eutectic Sn-Pb non-composite. The growth rate of the intermetallic layers were similar for both the eutectic Sn-Ag and eutectic Sn-Ag composite throughout the aging duration. The activation energies for Cu₆Sn₅ layer growth for the eutectic Sn-Pb and Sn-Ag solder joints are evaluated to be 111 kJ/mol and 116 kJ/mol, respectively. The eutectic Sn-Pb and Sn-Ag composite solder joints exhibit higher activation energies of 161 kJ/mol and 203 kJ/mol.     

Intermetallic compounds formed during the reflow of In-49Sn solder ball-grid array packages

The intermetallic compounds formed at the interfaces between In-49Sn solder balls and Au/Ni/Cu pads during the reflow of In-49Sn solder, ball-grid array (BGA) packages are investigated. Various temperature profiles with peak temperatures ranging from 140°C to 220°C and melting times ranging from 45 sec to 170 sec are plotted for the reflow processes. At peak temperatures below 170°C, a continuous double layer of intermetallics can be observed, showing a composition of Au(In,Ni)₂/Au(In,Ni). Through selective etching of the In-49Sn solders, the intermetallic layer is made up of irregular coarse grains. In contrast, a number of cubic-shaped AuIn₂ intermetallic compounds appear at the interfaces and migrate toward the upper domes of In-49Sn solder balls after reflow at peak temperatures above 200°C for longer melting times. The upward floating of the AuIn₂ cubes can be explained by a thermomigration effect caused by the temperature gradient present in the liquid solder ball. The intermetallic compounds formed under various reflow conditions in this study exhibit different types of morphology, yet the ball shear strengths of the solder joints in the In-49Sn BGA packages remain unaffected.     

Fabrication of 0.95Sn−0.05Au solder micro-bumps for flip-chip bonding

This letter describes the successful fabrication of a 0.95Sn−0.05Au solder microbump on a compound semiconductor wafer by reflowing of multi-layer metal film. Since the inherent interdiffusion in Au−Sn phases results in the alloying of multi-layer films, the composition of micro-bump is well controlled by the thickness of constituent metal films. The micro-bumps melt at about 220 C, which is close to the lowest eutectic temperature in a Au−Sn system. Solder bonding using 0.95Sn−0.05Au micro-bump is a very useful technique for the flipchip bonding of compound semiconductor devices.     

Inhibiting the formation of (Au1−xNix)Sn4 and reducing the consumption of Ni metallization in solder joints

The effects of adding a small amount of Cu into eutectic PbSn solder on the interfacial reaction between the solder and the Au/Ni/Cu metallization were studied. Solder balls of two different compositions, 37Pb-63Sn (wt.%) and 36.8Pb-62.7Sn-0.5Cu, were used. The Au layer (1 ± 0.2 μm) and Ni layer (7 ± 1 μm) in the Au/Ni/Cu metallization were deposited by electroplating. After reflow, the solder joints were aged at 160°C for times ranging from 0 h to 2,000 h. For solder joints without Cu added (37Pb-63Sn), a thick layer of (Au_1−xNi_x)Sn₄ was deposited over the Ni₃Sn₄ layer after the aging. This thick layer of (Au_1−xNi_x)Sn₄ can severely weaken the solder joints. However, the addition of 0.5wt.%Cu (36.8Pb-62.7Sn-0.5Cu) completely inhibited the deposition of the (Au_1−xNi_x)Sn₄ layer. Only a layer of (Cu_1-p-qAu_pNi_q)₆Sn₅ formed at the interface of the Cu-doped solder joints. Moreover, it was discovered that the formation of (Cu_1-p-qAu_pNi_q)₆Sn₅ significantly reduced the consumption rate of the Ni layer. This reduction in Ni consumption suggests that a thinner Ni layer can be used in Cu-doped solder joints. Rationalizations for these effects are presented in this paper.     

Stress relaxation behavior of eutectic tin-lead solder

The creep behavior of eutectic tin-lead solder was investigated using stress relaxation techniques. Stress relaxation experiments were performed on cast tensile specimens of commercial eutectic tin-lead solder, SN63. The sample casting conditions were controlled to produce microstructures similar to those found in typical solder joints on electronic assemblies. The stress relaxation data was analyzed to extract constitutive relations for creep. The strain rate during relaxation was found to follow two power law expressions, one with n = 3.2 at low stress levels and the other with n = 6.2 at higher stress levels. The apparent activation energy for creep and the power law exponent are discussed with relation to the published data for this alloy.     

Au／Sn与p—HgCdTe的欧姆接触

研究了双层金属结构Ａｕ／Ｓｎ与ｐ－ＨｇＣｄＴｅ上的接触电阻，实验测得Ａｕ／Ｓｎ与ｐ－Ｈｇ１－ｘＣｄＴｅ（ｘ＝０．２１７，０．４１）的经接触电阻，ρｃ（２９５Ｋ，７７Ｋ）为１０＾－２～１０＾４Ω．ｃｍ＾２将这种电板接触应用于Ｈｇ１－ｘＣｄｘＴｅ（ｘ＝０．２３）光伏器件，测得ｐｎ结Ｉ－Ｖ特性的正向斜率为１２．６Ω即电极接触电阻小于１２．６Ω。     

Reaction characteristics of the Au-Sn solder with under-bump metallurgy layers in optoelectronic packages

The reaction characteristics of molten Au/Sn eutectic solder with potential diffusion-barrier materials of optoelectronic packages were investigated. The characteristics were studied by reflowing the solder on Pt, Ni, and Co plates, respectively, and by measuring the thickness of the reaction product. In addition, the dissolution rate of Pt into the solder was measured. The results indicated that Pt, which is commonly used as the diffusion-barrier layer in the under-bump metallurgy (UBM) of optoelectronic packages, reacts readily with the molten solder, resulting in discontinuous reaction products at the solder/Pt interface. Cobalt, on the other hand, reacted with the solder at an order of magnitude slower rate than that of Pt and provided an effective barrier against the reaction with the solder.     

SnAgCuY钎料表面Sn晶须的旋转生长现象

研究了Sn3.8Ag0.7Cu1.0Y钎料表层上YSn3稀土相表面Sn晶须的生长行为。结果表明:室温时效条件下在YSn3的表面会出现Sn晶须的快速生长现象,生长速度最快可达10–10m/s,长度最长可达200μm。YSn3稀土相氧化的不均匀性是导致Sn晶须在生长时产生各种旋转现象的主要原因。     

Effect of microstructure of Au80Sn20 solder on the thermal resistance TO56 packaged GaN-based laser diodes

Au80Sn20 alloy is a widely used solder for laser diode packaging. In this paper, the thermal resistance of GaN-based blue laser diodes packaged in TO56 cans were measured by the forward voltage method. The microstructures of Au80Sn20 solder were then investigated to understand the reason for the difference in thermal resistance. It was found that the microstructure with a higher content of Au-rich phase in the center of the solder and a lower content of (Au,Ni)Sn phase at the interface of the solder/heat sink resulted in lower thermal resistance. This is attributed to the lower thermal resistance of Au-rich phase and higher thermal resistance of (Au,Ni)Sn phase.     

低银无铅焊膏板级封装工艺和焊点可靠性试验

针对低Ag无铅焊膏的市场需求,研究开发了一种适用于99.0Sn0.3Ag0.7Cu低Ag无铅焊膏用松香型无卤素助焊剂(WTO—LF3000),配制了相应的无铅焊膏(WTO—LF3000—SAC0307),并对其板级封装工艺适应性及焊点可靠性进行了考察,用测试后样品的电气可靠性作为接头可靠性评价条件。结果表明:所开发的低Ag无铅焊膏熔点和润湿性符合产品实际要求。配制的焊膏印刷质量良好,焊点切片观察其孔隙率<25%,满足行业标准IPC—A—610D之要求。样品分别经跌落、震动和温度循环试验后,无焊点脱落等现象,电气功能正常。     

Intermetallic reactions in Sn3Ag0.5Cu and Sn3Ag0.5Cu0.06Ni0.01Ge solder BGA packages with Au/Ni surface finishes

The intermetallic compounds (IMCs) formed during the reflow and aging of Sn3Ag0.5Cu and Sn3Ag0.5Cu0.06Ni0.01Ge solder BGA packages with Au/Ni surface finishes were investigated. After reflow, the thickness of (Cu, Ni, Au)₆Sn₅ interfacial IMCs in Sn3Ag0.5Cu0.06Ni0.01Ge was similar to that in the Sn3Ag0.5Cu specimen. The interiors of the solder balls in both packages contained Ag₃Sn precipitates and brick-shaped AuSn₄ IMCs. After aging at 150°C, the growth thickness of the interfacial (Ni, Cu, Au)₃Sn₄ intermetallic layers and the consumption of the Ni surface-finished layer on Cu the pads in Sn3Ag0.5Cu0.06Ni0.01Ge solder joints were both slightly less than those in Sn3Ag0.5Cu. In addition, a coarsening phenomenon for AuSn₄ IMCs could be observed in the solder matrix of Sn3Ag0.5Cu, yet this phenomenon did not occur in the case of Sn3Ag0.5Cu0.06Ni0.01Ge. Ball shear tests revealed that the reflowed Sn3Ag0.5Cu0.06Ni0.01Ge packages possessed bonding strengths similar to those of the Sn3Ag0.5Cu. However, aging treatment caused the ball shear strength in the Sn3Ag0.5Cu packages to degrade more than that in the Sn3Ag0.5Cu0.06Ni0.01Ge packages.     

Creep properties of eutectic Sn-3.5Ag solder joints reinforced with mechanically incorporated Ni particles

The creep deformation behavior of eutectic Sn-3.5Ag based Ni particle rein forced composite solder joints was investigated. The Ni particle reinforced composite solder was prepared by mechanically dispersing 15 vol.% of Ni particles into eutectic Sn-3.5Ag solder paste. Static-loading creep tests were carried out on solder joint specimens at 25 C, 65 C, and 105 C, representing homologous temperatures ranging from 0.6 to 0.78. A novel-design, miniature creep-testing frame was utilized in this study. Various creep parameters such as the global and localized creep strain, steady-state creep rate, onset of tertiary creep and the activation energy for creep were quantified by mapping the distorted laser ablation pattern imprinted on the solder joint prior to testing. The Ni-reinforced composite solder joint showed improved creep resistance compared to the results previously reported for eutectic Sn-3.5Ag solder, Sn-4.0Ag-0.5Cu solder alloys, and for eutectic Sn-3.5Ag solder reinforced with Cu or Ag particle reinforcements. The activation energy for creep was ∼0.52 eV for Sn-3.5Ag and Sn-4Ag-0.5Cu solder alloys. The activation energies ranged from 0.55–0.64 eV for Cu, Ag, and Ni reinforced composite solder joints, respectively. Most often, creep fracture occurred closer to one side of the solder joint within the solder matrix.     

Alloying effects in near-eutectic Sn-Ag-Cu solder alloys for improved microstructural stability

This study included a comparison of the baseline Sn-3.5Ag eutectic to one near-eutectic ternary alloy, Sn-3.6 Ag-1.0Cu and two quaternary alloys, Sn-3.6Ag-1.0Cu-0.15Co and Sn-3.6Ag-1.0 Cu-0.45 Co, to increase understanding of the beneficial effects of Co on Sn-Ag-Cu solder joints cooled at 1–3 C/sec, typical of reflow practice. The results indicated that joint microstructure refinement is due to Co-enhanced nucleation of the Cu₆Sn₅ phase in the solder matrix, as suggested by Auger elemental mapping and calorimetric measurements. The Co also reduced intermetallic interface faceting and improved the ability of the solder joint samples to maintain their shear strength after aging for 72 hr at 150 C. The baseline Sn-3.5Ag joints exhibited significantly reduced strength and coarser microstructures.     

Creep behavior of eutectic Sn-Cu lead-free solder alloy

Due to a typographical error incorporated during the editing process, the following is a correction of that error. Tensile creep behavior of precipitation-strengthened tin-based eutectic Sn-0.7Cu alloy was investigated at three temperatures ranging from 303 to 393 K. The steady-state creep rates cover six orders of magnitude (10⁻³ s⁻¹ to 10⁻⁸ s⁻¹) under the stress range of σ/E=10⁻⁴ to 10⁻³. The initial microstructure reveals that intermetallic compound Cu₆Sn₅ is finely dispersed in the matrix of β-Sn. By incorporating a threshold stress, σ_th, into the analysis, the creep data of eutectic Sn-Cu at all temperatures can be fitted by a single straight line with a slope of 7 after normalizing the steady-state creep rate and the effective stress, indicating that the creep rates are controlled by the dislocation pipe diffusion in tin matrix. So the steady-state creep rate, , can be expressed as , where Q_C is the active energy for creep, G is the temperature-dependent shear modulus, b is the Burgers vector, R is the universal gas constant, T is the temperature, σ is the applied stress, A is a material-dependent constant, and σ_th=σ_OB√1−k _R ² , in which σ_oB is the Orowan bowing stress and k_R is the relaxation factor. J. Electron. Mater. 31(5)(2002), pp.442–448. The online version of the original article can be found at     

高功率二极管激光器Au80Sn20焊料焊接实验研究

半导体激光器封装工艺过程对于激光器的输出特性、寿命等性能有重要影响,其中焊料的选择和焊接工艺是最关键的因素。本文采用磁控溅射的方法,在 WCu 热沉上制备了Au80Sn20合金焊料,取代了传统的In焊料,并对焊接工艺进行了改进。国外沉积的和我们制备的Au80Sn20合金焊料焊接DL芯片后的性能参数很接近。充分说明双靶分层溅射镀膜可以实现二极管激光器的封装要求,从而为优化半导体激光器制备工艺和提高半导体激光器的性能奠定基础。     

Creep behavior of eutectic Sn-Cu lead-free solder alloy

Tensile creep behavior of precipitation-strengthened, tin-based eutectic Sn-0.7Cu alloy was investigated at three temperatures ranging from 303–393 K. The steady-state creep rates cover six orders of magnitude (10⁻³−10⁻⁸ s⁻¹) under the stress range of σ/E=10⁻⁴−10⁻³. The initial microstructure reveals that the intermetallic compound Cu₆Sn₅ is finely dispersed in the matrix of β-Sn. By incorporating a threshold stress, σ _th, into the analysis, the creep data of eutectic Sn-Cu at all temperatures can be fitted by a single straight line with a slope of 7 after normalizing the steady-state creep rate and the effective stress, indicating that the creep rates are controlled by the dislocation-pipe diffusion in the tin matrix. So the steady-state creep rate, , can be expressed as exp , where Q_c is the activation energy for creep, G is the temperature-dependent shear modulus, b is the Burgers vector, R is the universal gas constant, T is the temperature, σ is the applied stress, A is a material-dependent constant, and , in which σ _OB is the Orowan bowing stress, and k_R is the relaxation factor. An erratum to this article is available at .     

Study of electromigration in eutectic SnPb solder stripes using the edge displacement method

Electromigration (EM) parameters in the eutectic SnPb solder were measured using the edge displacement method (EDM) and an atomic force microscope (AFM) in the temperature range of 60° to 140°C. The measured drift velocity was found to be 0.3 Å/sec when the solder stripe was stressed under 4.9×10⁴ A/cm² at 80°C, and it increased as the current density or the temperature increased. The products of DZ* at 60°C, 80°C, 100°C, 120°C, and 140°C were also obtained. In addition, the EM activation energy was determined to be 0.45 eV at the temperature range 60–100°C and 0.55 eV at the temperature range 100–140°C. These two activation energies may correspond to the Sn and Pb diffusion at the two temperature ranges. These values are very fundamental to current-carrying capability and mean-time-to-failure measurement for solder joints.     

调制型Au/Sn薄膜微观形貌及合金化工艺

采用Au和Sn单质金属靶,通过直流磁控溅射法制备调制型Au/Sn薄膜(薄膜层数为3～21),经快速退火后,实现单质多层薄膜的合金化.主要研究了Au/Sn薄膜微观形貌和合金化工艺控制.结果 表明,当固定薄膜总厚度为2 μm时,320℃下退火10 min后,膜层表面粗糙度与薄膜层数呈反比.薄膜层数较少(n=3)、调制周期厚...