微量Ni对Sn-3.0Ag-0.5Cu钎料及焊点界面的影响

研究了Ni的含量对无铅钎料Sn-3.0Ag-0.5Cu润湿性、熔点、重熔及老化条件下界面化合物(IMC)的影响。结果表明:微量Ni的加入使SnAgCu润湿力增加6%;使合金熔点略升高约3℃;重熔时在界面形成了(Cu,Ni)6Sn5IMC层,且IMC厚度远高于SnAgCu/Cu的Cu6Sn5IMC厚度。在150℃老化过程中,SnAgCuNi/Cu重熔焊点IMC随着时间的增加,其增幅小于SnAgCu/Cu的增幅,此时Ni对IMC的增长有一定抑制作用。     

BGA焊点的质量控制

BGA是现代组装技术的新概念,它的出现促进SMT(表面贴装技术)与SMD(表面贴装元器件)的发展和革新,并将成为高密度、高性能、多功能及高I/O数封装的最佳选择.本文结合实际工作中的一些体会和经验,就BGA焊点的接收标准、缺陷表现及可靠性等问题展开论述,特别对有争议的一种缺陷空洞进行较为详细透彻的分析,并提出一些改善BGA焊点质量的工艺改进的建议.     

电子产品实施无铅化是一个系统工程

从六个方面内容进行了评述,并强调了电子产品实施无铅化是一个系统工程。企图从电子产品实施无铅化的提出、无铅化焊料的基本特性、无铅化焊料焊接时的特点与要求等出发,从而论述电子产品实施无铅化对电子元器(组)件、CCL基板材料、PCB基板的主要要求以及相关的测试与标准的制定等,其目的是使读者有一个较全面的了解,以利于电子产品(包含原材料、元器件、PCB、组装等)制造者、特别是相关的工程技术人员,从整体的关联或系统工程上来理解、研究和解决电子产品无铅化问题,使电子产品能顺利而迅速地从有铅化(锡-铅体系)时代过渡到无铅化(目前,最佳体系为锡-银-铜系列)时代。     

波峰焊接工艺技术的研究

作为一种传统焊接技术,目前波峰焊依然在电子制造领域发挥着积极作用。本文介绍了波峰焊接技术的原理,并分别从焊接前的质量控制、生产工艺材料及工艺参数这三个方面探讨了提高波峰焊质量的有效方法。     

Ambient Temperature Ultrasonic Bonding of Si-Dice Using Sn-3.5wt.%Ag

Ultrasonic bonding of Si-dice to type FR-4 printed circuit boards (PCB) with Sn-3.5wt.%Ag solder at ambient temperature was investigated. The under-bump metallization (UBM) on the Si-dice comprised Cu/Ni/Al from top to bottom with thicknesses of 0.4 μm, 0.4 μm, and 0.3 μm, respectively. The pads on the PCBs consisted of Au/Ni/Cu with thicknesses of 0.05/5/18 μm, sequentially from top to bottom. Solder was supplied as Sn-3.5wt.%Ag foil rolled to 100 μm thickness, and inserted in the joints. The ultrasonic bonding time was varied from 0.5 s to 3.0 s, and the ultrasonic power was 1400 W. The experimental results showed that reliable joints could be produced between the Si-dice and the PCBs with Sn-3.5wt.%Ag solder. The joint breaking force of “Si-die/solder/FR-4” increased with bonding times up to 2.5 s with a maximum value of 65 N. A bonding time of 3.0 s proved to be excessive, and resulted in cracks along the intermetallic compound between the UBM and solder, which caused a decrease in the bond strength. The intermetallic compound produced by ultrasonic bonding between the UBM and solder was confirmed to be (Cu, Ni)₆Sn₅. An erratum to this article can be found at     

Interfacial Intermetallic Growth and Strength of Composite Lead-Free Solder Alloy Through Isothermal Aging

The effects of particle reinforcement of Sn-4.0wt.%Ag-0.5wt.%Cu (SAC405) lead-free solder on interfacial intermetallic layer growth and strength of the ensuing joints through short-term isothermal aging (150°C) were studied. Composite solders were prepared by either incorporating 2 wt.% Cu (3 μm to 20 μm) or Cu₂O (∼150 nm) particles into SAC405 paste. Aggressive flux had the effect of reducing the Cu₂O nanoparticles into metallic Cu which subsequently reacted with the solder alloy to form the Cu₆Sn₅ intermetallic. While all solders had similar interfacial intermetallic growth upon reflow, both of the composite solders’ growth rates slowed through aging to reach a common growth rate exponent of approximately 0.38, considerably lower than that of the nonreinforced solder (n = 0.58). The nanoscale reinforced solder additionally exhibited the highest tensile strength in both the initial and aged conditions, behavior also attributed to its quick conversion to a stable microstructure.     

片式电阻混合焊点热循环负载可靠性研究

对在不同工艺参数下形成的、并且经过不同周数热循环负载的片式电阻混合焊点、有铅焊点和无铅焊点进行了外观检测和剪切测试。结果显示,在不同工艺参数下形成的混合焊点的剪切力,随热循环周数的变化趋势有所不同,但是在保证片式电阻焊端和焊料充分熔融的情况下,部分混合焊点的平均剪切力比有铅焊点高,热循环1 000周后,为9.1～11.1 N。     

Interfacial Reactions between Eutectic SnZn Solder and Bulk or Thin-Film Cu Substrates

Interfacial reactions between eutectic SnZn solder and bulk or thin-film Cu substrates are investigated and compared. The thicknesses of bulk and thin-film Cu substrates are 0.5 mm and 4,000 ?, respectively. Different dominant reaction products and interfacial microstructures are observed in these two types of interfacial reactions. In the bulk Cu type, the Cu₅Zn₈ phase is the dominant reaction product under reflow and solid-state annealing. However, the CuZn₅ phase becomes the dominant reaction product in the thin-film Cu type. The Cu₅Zn₈ phase in the bulk Cu type remains as a uniform microstructure after reflow. After solid-state annealing, however, the Cu₅Zn₈ phase fractures and the Cu₆Sn₅ and Cu₃Sn phases are formed at the Cu₅Zn₈/Cu interface. The CuZn₅ phase in the thin-film Cu type ripens after reflow and the phase morphology is transformed from a uniform layer into separated scallops. In situ observation of the interfacial microstructure after solid-state annealing reveals that prominent deformation occurs in the solder region close to the interface in the bulk Cu type. While in the thin-film Cu type, the CuZn₅ grain is extruded out of the interface.     

Elevated temperature aging of solder joints based on Sn-Ag-Cu: Effects on joint microstructure and shear strength

The shear strength behavior and microstructural effects after aging for 100 h and 1,000 h at 150°C are reported for near-eutectic Sn-Ag-Cu (SAC) solder joints (joining to Cu) made from Sn-3.5Ag (wt.%) and a set of SAC alloys (including Co- and Fe-modified SAC alloys). All joints in the as-soldered and 100-h aged condition experienced shear failure in a ductile manner by either uniform shear of the solder matrix (in the strongest solders) or by a more localized shear of the solder matrix adjacent to the Cu₆Sn₅ interfacial layer, consistent with other observations. After 1,000 h of aging, a level of embrittlement of the Cu₃Sn/Cu interface can be detected in some solder joints made with all of the SAC alloys and with Sn-3.5Ag, which can lead to partial debonding during shear testing. However, only ductile failure was observed in all solder joints made from the Co- and Fe-modified SAC alloys after aging for 1,000 h. Thus, the strategy of modifying a strong (high Cu content) SAC solder alloy with a substitutional alloy addition for Cu seems to be effective for producing a solder joint that retains both strength and ductility for extended isothermal aging at high temperatures.     

Interfacial Reaction Between Cu Substrates and Zn-Al Base High-Temperature Pb-Free Solders

Chemical reactions between Cu substrates and Zn-Al high-temperature solder alloys, Zn-4Al and Zn-4Al-1Cu (mass%), at temperatures ranging from 420°C to 530°C were experimentally investigated by a scanning electron microscope using backscattered electrons (SEM-BSE) and an electron probe microanalyzer (EPMA). Intermediate phases (IMPs), β(A2) or β′(B2), γ(D8₂), and ε(A3) phases formed and grew during the soldering and aging treatments. The consumption rate of the IMP for Cu substrates is described by the square root of t in both the alloys, while the additional Cu in the molten Zn-Al alloy slightly suppresses the consumption of Cu substrates. The growth of IMPs during soldering treatment is controlled by the volume diffusion of constituent elements, and its activation energy increases in the order of Q _ε < Q _γ < Q _β. In view of the aging process, the growth of IMPs is considered to be controlled by the volume diffusion. In particular, the layer thickness of γ rapidly grows over 200°C, although the thickness of the β layer grows very slowly.