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。     

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。     

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。     

Sn基钎料与Cu和Al基板的润湿性比较研究

采用润湿平衡法测量了四种Sn基钎料(Sn-37Pb、Sn-3.OAg-0.5Cu、Sn-0.7Cu与Sn-9Zn)分别在250,260和270℃与Cu、Al两种基板的润湿性能.结果表明:钎料与Al基板的润湿时间均比Cu基板长,除Sn-9Zn外,其他三种钎料与Cu基板的润湿力比Al基板大,并且随着温度升高,润湿性能提高,...     

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。     

无铅焊料Sn-Zn-In系列合金的研究

对熔化起始温度和终止温度作线性回归进行合金设计,并对其焊料合金进行了熔点、抗剪切强度及微观组织等研究分析。结果表明:当w(In)(质量分数)为3%~5%,w(Zn)为5%~9%时,焊料的熔化温度在170~200℃,接近于焊料Sn-37Pb的熔化温度183℃;焊料与Cu焊合后形成γ-Cu5Zn8化合物;Sn-Zn-In系焊料的抗剪切强度与焊料Sn-37Pb的剪切强度33.73 MPa相当。     

无铅电子封装Sn-Cu焊料润湿性试验研究

为了改善无铅焊料的润湿性,配置活性剂松香焊剂和无机物焊剂,研究了Sn-0.75 Cu焊料的润湿性.分析讨论了影响Sn-0.75 Cu焊料润湿性的主要因素,获得了焊剂和Sn-0.75 Cu焊料的最优匹配.在镀锡铜片上,5#焊剂匹配Sn-0.75 Cu焊料能够获得最佳的润湿性(润湿角为18°),已接近Sn-37 Pb焊料的润湿性.     

微合金化对Sn-9Zn基无铅钎料润湿性能的影响

熔炼制备了纯的以及含微量Al、Mg、Ti、Bi、重稀土Y、混合轻稀土RE和一种富P非金属活性组元NM的Sn-9Zn基合金,通过测量这些合金以及商用Sn-37Pb焊料在铜基板上的铺展面积比较了它们对铜的润湿性能。结果表明Al、Ti和 Mg不利于提高合金在铜上的润湿性或附着力;Y的改善作用不大;而Bi、RE和NM则能明显改善Sn-9Zn合金对铜的润湿性。在此基础上进一步研究了RE和NM含量对Sn-9Zn润湿性能的影响。以铺展面积衡量,本研究所达到的最佳改善效果使Sn-9Zn合金对铜的润湿性由Sn-37Pb焊料润湿性水平的45.4%提高到了70.3%。     

典型Sn基焊料凸点互连结构电迁移异同性

研究了Sn37Pb,Sn3.0Ag0.5Cu和Sn0.7Cu三种焊料BGA焊点在电迁移作用下界面的微观组织结构.在60℃,1×103 A/cm2电流密度条件下通电187h后,Sn37 Pb焊点阴极界面已经出现了空洞,同时在阳极有Pb的富集带;Sn3.0Ag0.5Cu焊点的阴极界面Cu基体大量溶解,阳极金属间化合物层明显比阴极厚;对于Sn0.7Cu焊料,仅发现阳极金属间化合物层厚度比阴极厚,阴极Cu基体的溶解不如SnAgCu明显,电迁移破坏明显滞后.     

Characterization of lead-free solders and under bump metallurgies for flip-chip package

A variety of Pb-free solders and under bump metallurgies (UBMs) was investigated for flip chip packaging applications. The result shows that the Sn-0.7Cu eutectic alloy has the best fatigue life and it possess the most desirable failure mechanism in both thermal and isothermal mechanical tests regardless of UBM type. Although the electroless Ni-P UBM has a much slower reaction rate with solders than the Cu UBM, room temperature mechanical fatigue is worse than on the Cu UBM when coupled with either Sn-3.8Ag-0.7Cu or Sn-3.5Ag solder. The Sn-37Pb solder consumes less Cu UBM than all other Pb-free solders during reflow. However, Sn-37Pb consumes more Cu after solid state annealing. Studies on aging, tensile, and shear mechanical properties show that the Sn-0.7Cu alloy is the most favorable Pb-free solder for flip chip applications. When coupled with underfill encapsulation in a direct chip attach (DCA) test device, the Sn-0.7Cu bump with Cu UBM exhibits a characteristic life or 5322 cycles under -55/spl deg/C/+150/spl deg/C air-to-air thermal cycling condition.     

Effect of Thermal Aging on Impact Absorbed Energies of Solder Joints Under High-Strain-Rate Conditions

This study was concerned with the effect of thermal aging on the impact properties of solder joints. Three kinds of solders, conventional Sn-37Pb solder, Sn-3.8Ag-0.7Cu solder, and Sn-3.8Ag-0.7Cu doped with rare-earth (RE) elements, were selected to manufacture joint specimens for the Charpy impact test. U-notch specimens were adopted and isothermally aged at 150°C for 100 h and 1000 h, and then impacted by using a pendulum-type impact tester at room temperature. The Sn-37Pb solder joints exhibited higher performance in terms of impact absorbed energy in the as-soldered and 100 h thermally aged conditions. Interestingly, the Sn-3.8Ag-0.7Cu solder joints exhibited improved performance for the impact value after 1000 h of thermal aging. For the Sn-37Pb and Sn-3.8Ag-0.7Cu solder joints, the impact absorbed energies initially increased when the storage duration was limited to 100 h, and then gradually decreased with its further increase. For the Sn-3.8Ag-0.7Cu-RE specimens, impact performance decreased directly with increasing thermal aging. Furthermore, scanning electron microscopy (SEM) observation showed that the fracture paths were focused on the interface zone for the three kinds of joints in the aged conditions. For the Sn-37Pb joints, the fracture surfaces mainly presented a ductile fracture mode. For the Sn-3.8Ag-0.7Cu joints, with microstructure coarsening, crack propagation partly shifted towards the Sn/Cu₆Sn₅ interface. Compared with the 100 h aged joints, the area fraction of intergranular fracture of Sn grains on the Sn-3.8Ag-0.7Cu fracture surfaces was increased when the aging time was 1000 h. On the contrary, the fracture morphologies of Sn-3.8Ag-0.7Cu-RE were mainly brittle as thermal aging increased. Thus, an interrelationship between impact energy value and fracture morphology was observed.     

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.     

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.     

Comparison of Impact Toughness and Fracture Morphologies Between Pb-Containing and Pb-Free Solder Joints Subject to the Charpy Impact Test

Charpy impact tests on three kinds of as-soldered U-notch specimens were performed with reference to the American Society of Testing Materials (ASTM) standard E23-07 by using a pendulum-type impact tester at room temperature. Three kinds of solders, conventional Sn-37Pb, Sn-3.8Ag-0.7Cu, and Sn-3.8Ag-0.7Cu doped with rare-earth (RE) elements, were selected to fabricate the joint specimens for the impact test. The three joints demonstrate similar impact toughness values, with averages of 11.4 kJ/m², 10.4 kJ/m², and 11.0 kJ/m², respectively. Under observation by scanning electron microscopy (SEM), the Sn-37Pb joint exhibited mainly ductile fracture morphology. Fractographic observations of lead-free joints exhibited a mixture of ductile and brittle morphologies. The addition of RE elements resulted in an impact toughness that was slightly higher than that of the Sn-3.8Ag-0.7Cu alloy. The impact toughness and the fracture mode were notably dependent on the type of solder. Additionally, the thickness of the intermetallic compound (IMC) layer had a remarkable influence on the fracture path and impact toughness of the solder joints. An erratum to this article can be found at     

Interfacial microstructure of Pb-free and Pb-Sn solder balls in the ball-grid array package

Ball-grid array (BGA) samples were aged at 155°C up to 45 days. The formation and the growth of the intermetallic phases at the solder joints were investigated. The alloy compositions of solder balls included Sn-3.5Ag-0.7Cu, Sn-1.0Ag-0.7Cu, and 63Sn-37Pb. The solder-ball pads were a copper substrate with an Au/Ni surface finish. Microstructural analysis was carried out by electron microprobe. The results show that a ternary phase, (Au,Ni)Sn₄, formed with Ni₃Sn₄ in the 63Sn-37Pb solder alloy and that a quaternary intermetallic phase, (Au,Ni)₂Cu₃Sn₅, formed in the Sn-Ag-Cu solder alloys. The formation mechanism of intermetallic phases was associated with the driving force for Au and Cu atoms to migrate toward the interface during aging.