Failure mechanism of lead-free solder joints in flip chip packages

The failure mechanisms of SnAgCu solder on Al/Ni(V)/Cu thin-film, underbump metallurgy (UBM) were investigated after multiple reflows and high-temperature storage using a ball shear test, fracture-surface analysis, and cross-sectional microstructure examination. The results were also compared with those of eutectic SnPb solder. The Al/Ni (V)/Cu thin-film UBM was found to be robust enough to resist multiple reflows and thermal aging at conditions used for normal production purposes in both SnAgCu and eutectic SnPb systems. It was found that, in the SnAgCu system, the failure mode changed with the number of reflows, relating to the consumption of the thin-film UBM because of the severe interfacial reaction between the solder and the UBM layer. After high-temperature storage, the solder joints failed inside the solder ball in a ductile manner in both SnAgCu and SnPb systems. Very fine Ag₃Sn particles were formed during multiple reflows in the SnAgCu system. They were found to be able to strengthen the bulk solder. The dispersion-strengthening effect of Ag₃Sn was lost after a short period of thermal aging, caused by the rapid coarsening of these fine particles.     

雾化介质对SnAgCu系无铅焊锡雾化粉末特性的影响

实验利用自行设计的超音速雾化制粉装置,研究了不同雾化介质对SnAgCu系无铅焊锡粉末有效雾化率、粒度分布及球形度的影响.结果表明:在一定雾化条件下,氦气雾化粉末具有最高的有效雾化率、良好的粒度分布,且球形度最好;氮气雾化的粉末具有较好的综合性能;与氦气、氮气相比,氩气雾化粉末综合性能较差;空气雾化粉末雾化率较高,但粉末较粗、表面粗糙.     

Interaction of intermetallic compound formation in Cu/SnAgCu/NiAu sandwich solder joints

The interaction between Cu/solder interface and solder/Ni interface at a Cu/SnAgCu/NiAu sandwich solder joint with various surface finishes and solder heights was investigated. The interfacial microstructure and composition of intermetallic compounds (IMCs) were characterized by a scanning electron microscope (SEM) equipped with energy-dispersive x-ray spectroscopy (EDX). The phase structure of IMC was identified by x-ray diffraction (XRD). It is found that ternary (Cu,Ni)₆Sn₅ IMCs form at both interfaces. The composition, thickness, and morphology of the ternary IMCs depend not only on the interface itself, but also on the opposite interface. That is to say, strong coupling effects exist between the two interfaces. Lattice parameters of (Cu,Ni)₆Sn₅ shrink with increasing Ni content, in agreement with Vegard’s law. The mechanism of ternary IMC formation and interface coupling effects are discussed in this paper.     

Controlling intermetallic compound growth in SnAgCu/Ni-P solder joints by nanosized Cu6Sn5 addition

Nanosized Cu₆Sn₅ dispersoids were incorporated into Sn and Ag powders and milled together to form Sn-3Ag-0.5Cu composite solders by a mechanical alloying process. The aim of this study was to investigate the interfacial reaction between SnAgCu composite solder and electroless Ni-P/Cu UBM after heating for 15 min. at 240°C. The growth of the IMCs formed at the composite solder/EN interface was retarded as compared to the commercial Sn3Ag0.5Cu solder joints. With the aid of the elemental distribution by x-ray color mapping in electron probe microanalysis (EPMA), it was revealed that the SnAgCu composite solder exhibited a refined structure. It is proposed that the Cu₆Sn₅ additives were pinned on the grain boundary of Sn after heat treatment, which thus retarded the movement of Cu toward the solder/EN interface to form interfacial compounds. In addition, wetting is an essential prerequisite for soldering to ensure good bonding between solder and substrate. It was demonstrated that the contact angles of composite solder paste was <25°, and good wettability was thus assured.     

SnAgCu(SnPb)/Ni和SnAgCu(SnPb)/Cu界面金属间化合物在热冲击过程中的生长规律

通过对SnAgCu（SnPb）／Ni和SnAgCu（SnPb）／Cu界面热）中击过程中金属间化合物（Intermetallic compound，IMC）生长规律的研究，以期更好的了解SnAgCu无铅焊料与Ni或Cu金属化层的相互匹配。结果表明固溶在焊料中的Cu或者Ni影响热）中击过程中界面IMC的演化。采用NiAu镀层时，IMC的生长速率比HASL（Hot Air Solder Level）镀层慢，并且界面没有Kirkendall孔洞生成，所以有更好的长期可靠性。采用SnAgCu焊料时，界面Kirkendall孔洞较SnPb焊料少，界面IMC的生长速率较SnPb焊料慢。     

SnAgCuEr系稀土无铅钎料的显微组织与性能研究

系统研究了添加微量稀土Er对Sn3.8Ag0.7Cu钎料合金显微组织和性能的影响,通过对钎料的熔化温度、润湿性能、接头剪切强度的测试及显微组织观察,指出含微量稀土的SnAgCuEr合金是性能优良的无铅钎料合金,同时确定了最佳的Er含量范围.     

焊膏SnAgCu焊锡微粉在有机酸溶液中的腐蚀与防护

电子产品多用焊膏焊接,其黏度稳定性常受某些酸性物质的腐蚀而下降,进而导致可焊性下降.研究了SnAgCu无铅焊锡微粉在0.1 mol/L 乙二酸水溶液和0.1 mol/L 乙二酸乙醇溶液中的常温腐蚀行为,以及添加16 mmol/L 缓蚀剂苯并三唑(BTA)对其腐蚀行为的影响,并对微粉的腐蚀与缓蚀机制进行了分析.结果表明:焊锡微粉在乙二酸水溶液中的腐蚀程度比在同浓度的乙二酸乙醇溶液中更为严重,且在乙二酸水溶液中微粉表面出现大量均匀分布的腐蚀沟槽,而在乙二酸乙醇溶液中只有少量点蚀痕迹;微粉表面的富锡相易被腐蚀;焊膏中加入BTA对焊锡微粉有良好的缓蚀保护作用,由此使焊膏黏度的稳定性得到保证.     

Sn晶须形态的研究

本文研究了稀土相表面Sn晶须的生长行为.研究结果表明,如果将稀土相暴露于空气中,在稀土相的表面会出现Sn晶须的快速生长现象,且Sn晶须在其快速生长过程中会表现出一些特殊的形态特征,如片状Sn晶须的形成、Sn晶须的多次连续转折现象、Sn晶须的变截面生长现象、Sn晶须的分枝与合并以及Sn晶须的搭接现象等.     

Creep behavior of SnAgCu solders with rare earth Ce doping

Extensive testing was carried out to study the effects of rare earth Ce doping on the properties of SnAgCu solder alloys.The addition of 0.03%(mass fraction) rare earth Ce into SnAgCu solder may improve its mechanical properties,but slightly lower its melting temperature.The tensile creep behavior of bulk SnAgCuCe solders was reported and compared with SnAgCu solders.It is found that SnAgCuCe solders show higher creep resistance than SnAgCu alloys.Moreover,Dorn model and Garofalo model are successfully used...     

Ni/P/Ce对SnAgCu抗氧化性能和结晶裂纹的影响

通过向Sn3.0Ag0.5Cu(SAC305)合金中添加微量的Ni,P和Ce元素,研究了各添加元素对合金钎料高温抗氧化性能和结晶裂纹的影响.结果表明,Ni元素的添加对钎料合金抗氧化性能没有很明显的改善,但明显地减少了合金表面结晶裂纹的总长度,抑制其产生;微量P元素的添加由于在合金钎料表面形成了复杂的致密新相,可以防止熔化钎料的表面直接与空气接触,明显改善了合金的抗氧化性能,但P元素的添加却增加了合金表面结晶裂纹的产生;Ce元素的添加恶化了钎料合金的抗氧化性,对合金表面的结晶裂纹抑制作用较小.