Room-temperature indentation creep of lead-free Sn-5%Sb solder alloy

Creep behavior of the lead-free Sn-5%Sb solder alloy was studied by long-time Vickers indentation testing at room temperature. Four different conditions of the material were examined. These were unhomogenized cast (UC), homogenized cast (HC), unhomogenized wrought (UW), and homogenized wrought (HW) conditions. Based on the steady-state power-law creep relationship, the stress exponents were determined through different methods of analysis, and in all cases, the calculated exponents were in good agreement. The stress exponent values of about 5 and 12, depending on the processing route of the material, are very close to those determined by room-temperature conventional creep testing of the same material reported in the literature. For the HW condition, the n value of about 5 together with a very fine grain size of 4.5 μm and a high volume fraction of second-phase particles of 8.6% may suggest that dislocation climb is the creep mechanism. For all other conditions with different grain sizes and second-phase volume fractions, however, the high n value of 12 implies that the operative creep mechanism is dislocation creep, which is independent of grain size.     

Effects of Ag and Al Additions on the Structure and Creep Properties of Sn-9Zn Solder Alloy

Creep behavior of the eutectic Sn-9Zn, Sn-9Zn-0.5Ag, and Sn-9Zn-0.5Al solder alloys was studied by impression testing under constant punching stress in the range of 60 MPa to 130 MPa and at temperatures in the range of 298 K to 370 K. Analysis of the data showed that, for all loads and temperatures, Sn-9Zn-0.5Al had the lowest creep rates and thus the highest creep resistance among all materials tested. The creep resistance of Sn-9Zn-0.5Ag was slightly lower than that of the Al-containing alloy. The enhanced creep behaviors of the ternary alloys are attributed to the presence of AgZn₃ and very fine Zn particles, which act as the main strengthening agents in the Sn-9Zn-0.5Ag and Sn-9Zn-0.5Al alloys, respectively. Assuming a power-law relationship between the impression rate and stress, average stress exponents of 6.9, 7.1, and 7.2 and activation energies of 42.1 kJ mol⁻¹, 42.9 kJ mol⁻¹, and 43.0 kJ mol⁻¹ were obtained for Sn-9Zn, Sn-9Zn-0.5Ag and Sn-9Zn-0.5Al, respectively. These activation energies are close to 46 kJ mol⁻¹ for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about 7, suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.     

Creep rupture of lead-free Sn-3.5Ag-Cu solders

Creep-rupture properties of lead-free Sn-3.5Ag-based alloys with varying amount of Cu were investigated using rolled and heat-treated dog-bone-shaped specimens. Nominal compositions of added copper were 0 wt.%, 0.5 wt.%, 0.75 wt.%, 1.0 wt.%, and 1.5 wt.%. During creep tests, the matrix hardness dropped significantly, and the minimum strain rates ( ) were lowest for the 0.75Cu specimens. The stress exponents (n) of were usually around 4, with the exception of the 0.5Cu and 0.75Cu alloys, which showed somewhat higher values of n. Fractographic analyses revealed typical creep rupture by the nucleation and growth of cavities in the matrix except the 1.5Cu specimens, which showed cavity nucleation at brittle Cu₆Sn₅ particles.     

Sn-0.7 Cu钎料的蠕变性能研究

采用一种微型圆形截面试件对Sn-0.7Cu在23,60,90,120℃时进行了蠕变性能研究。引入门槛应力值方法(threshold stress approach)来描述Sn-0.7Cu的蠕变性能。得出在低温区蠕变真实应力指数为7,高温区蠕变真实应力指数为5。并确定了Sn-0.7Cu的蠕变本构方程。     

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 .     

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     

Effect of Homogenization on the Indentation Creep of Cast Lead-Free Sn-5%Sb Solder Alloy

Creep behavior of cast lead-free Sn-5%Sb solder in unhomogenized and homogenized conditions was investigated by long time Vickers indentation testing under a constant load of 15 N and at temperatures in the range 321–405 K. Based on the steady-state power law creep relationship, the stress exponents were found for both conditions of the material. The creep behavior in the unhomogenized condition can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring around 11.7 × 10⁻⁴ < (H _V /E) < 18 × 10⁻⁴. The low stress regime activation energy of 54.2 kJ mol⁻¹, which is close to 61.2 kJ mol⁻¹ for dislocation pipe diffusion in the Sn, and stress exponents in the range 5.0–3.5 suggest that the operative creep mechanism is dislocation viscous glide. This behavior is in contrast to the high stress regime in which the average values of n = 11.5 and Q = 112.1 kJ mol⁻¹ imply that dislocation creep is the dominant deformation mechanism. Homogenization of the cast material resulted in a rather coarse recrystallized microstructure with stress exponents in the range 12.5–5.7 and activation energy of 64.0 kJ mol⁻¹ over the whole ranges of temperature and stress studied, which are indicative of a dislocation creep mechanism.     

微量RE和Al对Sn-9Zn焊料组织与性能的影响

采用正交试验研究了微量RE和Al对Sn-9Zn无铅焊料电导率、硬度、润湿性及微观组织的影响,并与传统锡铅焊料进行了对比。Sn-9Zn焊料的电性能及力学性能优于传统锡铅焊料,但润湿性较差。添加微量RE和Al可以显著提高Sn-9Zn合金铺展率、细化组织,且不降低焊料电导率和力学性能,最佳w(RE)和w(Al)分别为0.05%和0.10%,铺展率达到61.98%,与Sn-9Zn相比提高了13.40%,硬度为20.90HB,电导率为8.15×106S/m。     

无铅电子钎料合金蠕变性能研究

设计制作了一种简单可靠的弯折蠕变测量装置,比较了两种无铅电子钎料合金Sn-9Zn和Sn-3.5Cu-0.7Ag与传统电子钎料合金Sn-40Pb的常温蠕变性能,以及冷却条件对其蠕变强度的影响。结果表明:两种无铅钎料的抗蠕变性能大大优于传统锡铅钎料;Sn-3.5Ag-0.7Cu合金的抗蠕变性能优于Sn-9Zn合金;冷却速率对Sn-9Zn合金和Sn-3.5Ag-0.7Cu合金组织的影响类似,然而对蠕变强度的影响却相反:水冷使两种合金的组织相对于空冷都明显细化,Sn-9Zn合金的蠕变强度因之降低,而Sn-3.5Ag-0.7Cu合金的蠕变强度却因之提高。对可能产生的原因进行了讨论。     

微量锗对Sn-0.7Cu-0.05Ni钎料微观组织与性能的影响

为改善Sn-0.7Cu-0.05Ni钎料抗氧化性差及溶铜速率快的问题,向Sn-0.7Cu-0.05Ni钎料中添加微量锗,研究了不同锗添加量(质量分数0.01％～0.10％)对SnCuNi钎料合金显微组织及性能的影响.结果表明,微量的锗能显著细化Sn-0.7Cu-0.05Ni钎料合金组织,抑制金属间化合物的生长,改善合金的组织分布,提高钎料的润湿性及力学性能.此外,锗的添加还能显著提高钎料的抗氧化性并降低溶铜速率,当锗的质量分数从0增至0.10％时,溶铜速率从0.117 μm/s降至0.110 μm/s.     

Study on the microstructure of a novel lead-free solder alloy SnAgCu-RE and its soldered joints

This paper focused on the microstructure of SnAgCu-rare earth (RE) solder alloy and its small single-lap joints, focusing on phases present and the distribution of RE in the SnAgCu solder. Energy dispersive x-ray (EDX) analysis was used to observed the RE-rich phase. The RE atoms also tended to aggregate at boundaries of primary dendrites in the joints and form as a weblike structure, which surrounded the dendrites and restrained the dendrites from sliding or moving. It is assumed that this would strengthen the boundaries and increase the resistance to creep deformation of the solder matrix. The creep-rupture life of joints can be remarkably increased, at least seven times more than that of SnAgCu at room temperature. The aggregation mechanism of RE at dendrite boundaries in SnAgCu solder joints was presented. The drive for RE atoms to aggregate at the boundary is the difference of the lattice-aberration energy between the interior and the boundaries of the dendrites, which is caused by a solution of RE atoms.     

电阻法测量无铅焊点蠕变的有效性实验研究

为了解用于焊点性能评估的电阻测试法能否精确反映其蠕变特性,利用特制的焊点测试系统,同步采集无铅焊点在室温、25 N载荷下的电阻应变和剪切蠕变.实验表明它们的总体变化趋势相似,均可分为线性与指数阶段,但变化速率存在明显差异.两者临界拐点的延时程度与焊点的尺寸因子k有关,在一定的范围内(k= 4.5～8.5),延时程度仅在...     

纳米压痕法分析Sn-9Zn/Cu焊点力学性能

通过对Sn-9Zn/Cu焊点进行纳米压痕实验发现:在保载阶段,体钎料产生了明显的蠕变特征,蠕变深度随着加载速率的增加而增加.基于压痕做功概念确定了Sn-9Zn/Cu焊点中体钎料的蠕变应力指数n约为5.128.硬度和弹性模量测试结果表明:金属间化合物Cu5Zn8的压痕硬度(5.152±0.224) GPa约是体钎料压痕硬...     

The properties of Sn-9Zn lead-free solder alloys doped with trace rare earth elements

The Sn-Zn alloys have been considered as lead-free solders. It is well known that their poor properties of wetting and oxidation resistance are the main problems to prevent them from becoming commercially viable solders. In this paper, trace rare earth (RE) elements of mainly Ce and La have been used as alloying elements into the Sn-9Zn alloy. The results indicated that with the RE addition the originally coarse β-Sn grains in the microstructure of the alloy were refined. The tensile strength significantly increased with only a slight decrease in ductility. The surface tension was decreased, resulting in great improvement in wetting properties with rosin-based active flux.     

Effect of bismuth on the isothermal fatigue properties of Sn-3.5mass%Ag solder alloy

Sn-3.5mass%Ag eutectic solder is selected as a candidate base alloy for replacing the eutectic Sn-Pb, and the effect of bismuth (2, 5, 10mass%) on the fatigue life of bulk Sn-3.5mass%Ag eutectic at room temperature has been studied over the total strain range from 0.3 to 3 percent in tension-tension mode. Fatigue life is defined as the number of cycles at which the load decreases to a half of the initial value. The fatigue life dramatically decreases with increasing contents of bismuth and adding this element over 2% makes fatigue life shorter than that of tin-lead eutectic alloy. Tensile strength of the alloy significantly increases with an increase in bismuth contents due to solid solution hardening (<5%Bi) or dispersion strengthning of fine bismuth particles, while ductility of this system dramatically decreases with increasing bismuth contents. Fatigue life of these alloys depends on ductility obtained by tensile test. The fatigue life of Bi containing Sn-3.5%Ag alloys can be described by, (Δε_p/2D)·N _f ^0.59 =0.66 where N_f is fatigue life defined by number of cycles to one-half load reduction, Δε_p is the plastic strain range for initial cycles, D is the ductility as measured by reduction in area.     

稀土元素对Sn-0.2Ag-0.7Cu钎料合金物理性能的影响

在筛选出综合性能较好的Sn-0.2Ag-0.7Cu钎料合金中,添加微量混合稀土元素(RE)以提高钎料的焊接性能。研究了稀土的添加量对其熔化温度、电导率和固–液相线温差等焊接性能的影响。结果表明:添加w(RE)为0.1%~0.5%时,固–液相线温差小于15℃,符合现行钎焊工艺要求,且对钎料合金的熔化温度和电导率影响不大。     

Microstructure and mechanical properties of new lead-free Sn-Cu-RE solder alloys

The Sn-0.7%Cu alloy has been considered as a lead-free alternative to lead-tin alloys. In this work, various small amounts of rare earth (RE) elements, which are mainly Ce and La, have been added to the Sn-0.7%Cu alloy to form new solder alloys. It was found that the new alloys exhibit mechanical properties superior to that of the Sn-0.7%Cu alloy. In particular, the addition of up to 0.5% of RE elements is found to refine the effective grain size and provide a fine and uniform distribution of Cu₆Sn₅ in the solidified microstructure. Tensile, creep, and microhardness tests were conducted on the solder alloys. It was found that significant improvements of the tensile strength, microhardness, and creep resistance were obtained with RE element addition. Upon aging at 150°C for 20 h, the microstructure of Sn-Cu-RE is more stable than that of the Sn-Cu alloy.     

Sn-8Zn-3Bi无铅焊料的表面改性

采用液相法用有机物改性剂对Sn-8Zn-3Bi焊料进行表面包覆改性,以改善焊料的润湿性能及抗氧化性能。对包覆样品进行了红外光谱表征。考察了样品的抗氧化性、润湿性能和存储性能。结果表明:采用液相法可以实现在Sn-8Zn-3Bi焊料表面包覆有机物。以有机物C为改性剂,且用量为2%(质量分数)时得到的改性样品的润湿角θ为7.8°,铺展面积S为108.83mm2,而未被改性的焊料θ为10.74°,S为93.40mm2。     

Sn-0.3Ag-0.7Cu-xBi低银无铅钎料的润湿性

以Bi为添加剂对低银型Sn-0.3Ag-0.7Cu无铅钎料进行改性,应用SAT—5100型润湿平衡仪对Sn-0.3Ag-0.7Cu-xBi(x=0,1,3和4.5)钎料的润湿性能作了对比分析。结果表明:适量Bi元素的加入可以改善Sn-0.3Ag-0.7Cu钎料合金的润湿性能,且在240℃下Sn-0.3Ag-0.7Cu-3.0Bi无铅钎料具有最佳的润湿性能,在250℃其润湿力达到最大值3.2×10–3N/cm。     

Creep resistance of tin-based lead-free solder alloys

This paper reports on the microstructure-creep property relationship of three precipitation-strengthened tin (Sn)-based lead (Pb)-free solder alloys (Sn-0.7Cu, Sn-3.5Ag, and Sn-3.8Ag-0.7Cu) in bulk samples, together with Sn-37Pb as the alloy for comparison at temperatures of 303 K, 348 K, and 393 K. The creep resistance of these three Sn-based Pb-free solders increases, i.e., the steady-state creep rates decrease, with increasing volume fraction of precipitate phases for the Pb-free solder alloys. Their apparent stress exponents (n_a ∼ 7.3-17), which are all higher than that of pure Sn, attain higher values with increasing volume fraction of precipitate phases at constant temperature, and with decreasing temperature for the same solder alloy.