Sn-Cu、Sn-Ag-Cu系无铅钎料的钎焊特性研究

制备了Sn-0.7Cu、Sn-3.5Ag-0.6Cu钎料,用润湿平衡法测量了钎料对铜的润湿曲线,研究了温度、钎剂活性、钎焊时间对润湿行为的影响,并与Sn-37Pb钎料进行了比较。结果表明:升高温度能显著改善无铅钎料对铜的钎焊性。当温度<270℃时,Sn-0.7Cu的钎焊性明显低于Sn-3.5Ag-0.6Cu钎料;而当温度≥270℃时,两种钎料对铜都会显示较好的润湿性,而Sn-0.7Cu略优于Sn-3.5Ag-0.6Cu钎料。提高钎剂活性能显著增强钎料对铜的润湿性,其卤素离子的最佳质量分数均为0.4%左右。随着浸渍时间的延长,熔融钎料与铜的界面间产生失润现象。无铅钎料的熔点和表面张力较高,是钎焊性较差的根本原因。     

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。     

三种高Sn无铅钎料的表面张力和润湿性能研究

采用悬滴法测量了3种无铅钎料合金(Sn-3.0Ag-0.5Cu、Sn-0.7Cu与Sn-9.0Zn)在260℃时的表面张力,分别为525.5,534.8和595.4 mN/m;同时采用座滴法测量了其在260℃熔融状态下与Cu基板的接触角,分别为24.5°、28.0°和102.5°,并且与传统Sn-37.0Pb钎料进行了比较研究。结果表明,无铅钎料合金的表面张力与接触角均大于Sn-37.0Pb钎料。结合Young-Dupre公式讨论了钎料合金表面张力与其润湿性能的相关性,认为Sn基钎料合金在Cu基板上的润湿性能主要取决于其表面张力。     

Sn-3.7Ag-0.9Zn无铅钎料合金压入蠕变性能研究

采用自制的压入蠕变装置,研究了共晶型Sn-3.7Ag-0.9Zn无铅钎料合金在333~418K,压入应力为34.1~75.3MPa时的压入蠕变性能,并获得其稳态压入蠕变速率的本构方程;利用XRD和SEM对合金蠕变前后的成分和微观组织进行了分析。结果表明:Sn-3.7Ag-0.9Zn无铅钎料合金的应力指数n为4.6,蠕变激活能Qc为82.03kJ/mol,材料的结构常数A为1.74×10–5,其压入蠕变机制主要是由位错攀移运动控制的蠕变;金属间化合物Ag3Sn、AgZn提高了合金的抗压入蠕变性能。     

三种典型Sn-Ag-Cu无铅钎料的组织和性能研究

对比研究了三种典型标称成分的Sn-Ag-Cu钎料(即日本JEIDA推荐的Sn-3.0Ag-0.5Cu、欧盟IDEALS推荐的Sn-3.8Ag-0.7Cu和美国NEMI推荐的Sn-3.9Ag-0.6Cu)的显微组织特征、熔化特性、润湿性以及钎焊接头微焊点的力学性能等。结果表明,三种钎料的组织和性能非常接近。然而从性价比等方面综合考虑,Sn-3.0Ag-0.5Cu为三种钎料中最具优势的替代传统Sn-Pb钎料(共晶和近共晶钎料)的无铅合金。     

Ce对SnAgCu系无铅焊锡力学性能的影响

通过向Sn-3Ag-2.8Cu钎料合金中添加微量稀土Ce,利用扫描电子显微镜(SEM)研究了不同稀土含量对Sn-3Ag-2.8Cu合金的力学性能的影响,同时对显微组织进行了分析.实验结果表明,微量的Ce稀土可以显著提高Sn-3Ag-2.8Cu钎料的延伸率、延长其焊接接头在室温下的蠕变断裂寿命,尤其是当稀土的质量分数为0.1%时,其蠕变断裂寿命可以达到Sn-3Ag-2.8Cu钎料的9倍以上,当稀土的质量分数超过0.1%时,接头的蠕变断裂寿命呈下降趋势.综合考虑,最佳的稀土质量分数为0.05%～0.10%.     

微量元素对Sn-0.7Cu无铅钎料抗氧化性能的影响

以Sn-0.7Cu系无铅钎料合金为基础,添加微量的P、Ge、Ga、RE元素,进行了280℃大气环境下氧化试验,通过对含有不同微量元素的无铅钎料表面氧化状况的对比及分析,研究了不同微量元素对Sn-0.7Cu无铅钎料抗氧化性能的影响。发现当P和Ga同时添加时,得到Sn-0.7Cu-(0.001~0.1)P-(0.0001~0.1)Ga无铅钎料的抗氧化性能高于Sn-0.7Cu-(0.001~0.1)P和Sn-0.7Cu-(0.0001~0.1)Ga的抗氧化性能。     

低银Sn—Ag—Cu无铅钎料的性能研究

使用银含量较低的Sn-Ag-Cu无铅钎料是降低焊料成本最直接有效的手段之一,但银含量降低后对钎料性能的影响尚缺乏系统报导。通过向Sn-Cu二元体系中加入不同比例的纯银,制备了一系列低银合金。研究了银含量对钎料的熔点、可焊性及溶铜性能的影响。通过拉伸试验研究了合金的强度及杨氏模量。综合考虑上述各项性能指标,Sn-0.5Ag-0.7Cu是具有最佳性价比的合金成分。     

微量混合稀土对SnAgCu钎料合金性能的影响

通过向Sn-3.8Ag-0.7Cu钎料合金中添加微量的Ce基混合稀土，研究了不同稀土含量对SnAgCu合金物理性能、润湿性能及力学性能的影响，同时对显微组织进行了分析。试验结果表明，微量的混合稀土可以显著提高SnAgCu钎料接头在室温下的蠕变断裂寿命，尤其是当稀土的质量分数为0．1％时，其蠕变断裂寿命可以达到Sn-3.8Ag-0.7Cu钎料的7倍以上。通过对SnAgCuRE钎料合金物理、工艺及力学性能的测试，显微组织分析表明，随着稀土含量的增加，钎料的组织逐渐细化，但同时，稀土化合物的数量增多，对钎料的力学性能产生不利影响。综合考虑，最佳的稀土质量分数为0．05％－0．5％，不宜超过1．0％。     

P对Sn-Cu无铅钎料性能的影响

添加了P到Sn-Cu系无铅钎料中,测定了钎料的熔化温度、抗氧化性能和接头蠕变疲劳寿命。结果表明:在Sn0.7Cu中添加微量的P,提高了无铅钎料的抗氧化性能,对熔化温度基本无影响。Sn0.7Cu0.005P无铅钎料合金熔化温度的峰值为226.7℃,在恒定应力为2MPa的蠕变疲劳试验中,钎料接头蠕变疲劳寿命为337.357min。     

Creep Behavior of Lead-Free Sn-Ag-Cu + Ni-Ge Solder Alloys

We developed a new lead-free solder alloy, an Sn-Ag-Cu base to which a small amount of Ni and Ge is added, to improve the mechanical properties of solder alloys. We examined creep deformation in bulk and through-hole (TH)␣form for two lead-free solder alloys, Sn-3.5Ag-0.5Cu-Ni-Ge and Sn-3.0Ag-0.5Cu, at elevated temperatures, finding that the creep rupture life of the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy was over three times better than that of the Sn-3.0Ag-0.5Cu solder at 398 K. Adding Ni to the solder appears to make microstructural development finer and more uniform. The Ni added to the solder readily combined with Cu to form stable intermetallic compounds of (Cu, Ni)₆Sn₅ capable of improving the creep behavior of solder alloys. Moreover, microstructural characterization based on transmission electron microscopy analyses observing creep behavior in detail showed that such particles in the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy prevent dislocation and movement.     

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.     

Study of the Impact Performance of Solder Joints by High-Velocity Impact Tests

The impact behavior of solder joints was studied using three different high-velocity impact tests: the U-notch Charpy impact test, the no-notch Charpy impact test, and a laboratory-designed drop test. The solder joints were made of five solder alloys, Sn-37Pb, Sn-3.8Ag-0.7Cu, Sn-2.0Ag-0.7Cu, Sn-1.0Ag-0.7Cu, and Sn-0.7Ag-0.7Cu (in wt.%), in which the traditional Cu/solder/Cu butt joint was used. All three impact tests gave the same trend of the impact behavior of the solder joints, with the Sn-37Pb joints having the highest impact resistance and the Sn-3.8Ag-0.7Cu joints having the lowest impact resistance. For the lead-free joints, the Sn-1.0Ag-0.7Cu joints had better impact resistance than the Sn-2.0Ag-0.7Cu joints, and the Sn-2.0Ag-0.7Cu joints better than the Sn-0.7Ag-0.7Cu joints. The impact behavior was correlated well to the fracture morphologies observed by scanning electron microscopy (SEM). Comparison of the three tests showed that the no-notch Charpy impact test is a promising method for evaluating the drop performance of solder joints.     

Stress–Strain Characteristics of Tin-Based Solder Alloys for Drop-Impact Modeling

The stress–strain properties of eutectic Sn-Pb and lead-free solders at strain rates between 0.1 s⁻¹ and 300 s⁻¹ are required to support finite-element modeling of the solder joints during board-level mechanical shock and product-level drop-impact testing. However, there is very limited data in this range because this is beyond the limit of conventional mechanical testing and below the limit of the split Hopkinson pressure bar test method. In this paper, a specialized drop-weight test was developed and, together with a conventional mechanical tester, the true stress–strain properties of four solder alloys (63Sn-37Pb, Sn-1.0Ag-0.1Cu, Sn-3.5Ag, and Sn-3.0Ag-0.5Cu) were generated for strain rates in the range from 0.005 s⁻¹ to 300 s⁻¹. The sensitivity of the solders was found to be independent of strain level but to increase with increased strain rate. The Sn-3.5Ag and the Sn-3.0Ag-0.5Cu solders exhibited not only higher flow stress at relatively low strain rate but, compared to Sn-37Pb, both also exhibited higher rate sensitivity that contributes to the weakness of these two lead-free solder joints when subjected to drop impact loading.     

Creep and rupture behavior of Cu wire/lead-free solder-alloy joint specimen

Creep and rupture behavior of Cu wire/lead-free solder-alloy joint specimens have been investigated using Sn-3.5% Ag and Sn-0.5% Cu alloys. A Sn-37% Pb solder alloy is also used as a reference material. The present authors have fabricated a creep-rupture testing machine for Cu wire/solder-alloy joint specimens, performed creep and rupture tests at 303 K and 403 K, analyzed the characteristics of the creep and rupture behavior, and compared these to test specimens cut from the same alloy ingots. It is also found that the rupture strength of the joint specimens is related to the rupture strength of the alloys.     

Dissolution behavior of Cu and Ag substrates in molten solders

This study investigated the dissolution behavior of Cu and Ag substrates in molten Sn, Sn-3.5Ag, Sn-4.0Ag-0.5Cu, Sn-8.6Zn and Sn-8.55Zn-0.5Ag-0.1Al-0.5Ga lead-free solders as well as in Sn-37Pb solder for comparison at 300, 350, and 400°C. Results show that Sn-Zn alloys have a substantially lower dissolution rate of both Cu and Ag substrates than the other solders. Differences in interfacial intermetallic compounds formed during reaction and the morphology of these compounds strongly affected the substrate dissolution behavior. Soldering temperature and the corresponding solubility limit of the substrate elements in the liquid solder also played important roles in the interfacial morphology and dissolution rate of substrate.