Evolution of Ag3Sn at Sn-3.0Ag-0.3Cu-0.05Cr/Cu joint interfaces during thermal aging

The intermetallic compounds (IMC) in the solder and at the interface of Sn-3.0Ag-0.5Cu (SAC)/Cu and Sn-3.0Ag-0.3Cu-0.05Cr (SACC)/Cu joints were investigated after isothermal aging at 150 °C for 0, 168 and 500 h. Different shaped Ag₃Sn phases were found near the IMC layer of the latter joint. Interestingly, fine rod-shaped and branch-like Ag₃Sn were detected near the interface after soldering and long Ag₃Sn changed into shorter rods and small particles during aging. It is investigated that the Cr addition and thermal aging have effect on the evolution of Ag₃Sn morphologies and it is controlled by interfacial diffusion. Energy minimization theory and the redistribution of elements are used to explain the morphological evolution of Ag₃Sn. Small Ag₃Sn particles were also found on the IMC layer after aging, unlike the large Ag₃Sn at that of SAC/Cu joints. In conclusion, a favorable morphology of the joint interface leads to better bonding properties for SACC/Cu joints against thermal aging than that for SAC/Cu.     

镀镍多壁碳纳米管对Sn-3.0Ag-0.5Cu无铅钎料焊点界面行为的影响

采用机械混合法制备了不同含量(0、0.05、0.1、0.2、0.5wt%)镀镍多壁碳纳米管(Ni-CNTs)复合Sn-3.0Ag-0.5Cu(SAC305)无铅钎料。采用F4N回流炉对SAC305-x(Ni-CNTs)钎料进行回流焊,利用电热鼓风干燥箱对焊点试样进行170 ℃时效(t=0、48 h)处理。结合DTA、SEM、EDS等分析手段研究了不同镀镍碳纳米管含量对Sn-3.0Ag-0.5Cu钎料润湿性、熔点和焊点界面金属间化合物(IMC)层的影响。结果表明:Ni-CNTs可以显著改善钎料的润湿性,降低钎料熔点;此外,Ni-CNTs可以有效抑制界面IMC层的生长,同时改变界面IMC组成。综合比较得出Ni-CNTs最佳添加量为0.05%,与Sn-3.0Ag-0.5Cu钎料相比,润湿角降低49.76%,熔点降低0.331 ℃;时效后界面IMC层厚度4.292 μm(t=0 h)、5.238 μm(t=48 h)相对于SAC305钎料界面IMC厚度6.529 μm(t=0 h)、8.255 μm(t=48 h)分别降低了34.26%(t=0 h)、36.55%(t=48 h),界面IMC层相组成转变为(Cu_1-xNi_x)₆Sn₅和(Cu_1-xNi_x)₃Sn。     

Properties analysis of a new type of solder paste SACBN07

In this work,the wettability,aging and shear properties of a new type of lead-free solder paste Sn-07Ag-05Cu + BiNi (SACBN07) was investigated by conducting a series of comparison experiments with SAC305 and SAC0307 solder paste.The results show that weuability of SACBN07 is almost equal to SAC305,and better than that of SAC0307 solder paste.The thickness of intermetallic compound (IMC) layer in SACBN07/Cu is lower than that of other two types of solder joint after aging.And Cu3Sn layer of SACBN07/Cu is thinner than that of SAC305 and SAC0307.In addition,the SACBN07 solder joints perform the best shear strength among these three types of solder pastes.     

热老化与热循环条件下Bi对Sn-1.0Ag-0.5Cu无铅焊点界面组织与性能的影响

研究了在热老化和热循环过程中Bi的添加对低银无铅钎料Sn-1.0Ag-0.5Cu (SAC105)的BGA焊点界面微观组织演变的影响,分析了Bi的添加对SAC105微焊点热老化与热循环剪切性能的影响. 结果表明,Bi元素添加量为2%(质量分数)时,对热循环过程中微焊点界面处金属间化合物(IMC)层整体厚度的增加起到抑制作用,同时阻碍了热循环过程中因焊点热失配导致的IMC层破碎. 但是Bi的添加促进了界面IMC层中Cu₃Sn层的生长,因此在经过20天以上热老化处理后SAC105-2Bi微焊点界面IMC层厚度与SAC105微焊点接近. 此外,Bi的添加可以显著提升热循环处理后SAC105微焊点的抗剪切能力. SAC105-2Bi微焊点的剪切力学性能受到热循环处理的影响较小. 与SAC105微焊点相比,SAC105-2Bi微焊点的断裂模式更早地从韧性断裂向脆性断裂转变,因此Bi的添加降低了SAC105微焊点的热循环可靠性.     

Interfacial reactions and mechanical properties between Sn-4.0Ag-0.5Cu and Sn-4.0Ag-0.5Cu-0.05Ni-0.01Ge lead-free solders with the Au/Ni/Cu substrate

Sn-4.0Ag-0.5Cu (SAC) and Sn-4.0Ag-0.5Cu-0.05Ni-0.01Ge (SACNG) lead-free solders reacting with the Au/Ni/Cu multi-layer substrate were investigated in this study. All reaction couples were reflowed at 240 and 255 °C for a few minutes and then aged at 150 °C for 100-500 h. The (Cu, Ni, Au)₆Sn₅ phase was formed by reflowing for 3 min at the interface. If the reflowing time was increased to 10 min, both (Cu, Ni, Au)₆Sn₅ and (Ni, Cu, Au)₃Sn₄ phases formed at the interface. The AuSn₄ phase was found in the solder for all reaction couples. An addition of Ni and Ge to the solder does not significantly affect the IMC formation. After a long period of heat-treatment, the thickness of the (Cu, Ni, Au)₆Sn₅ and (Ni, Cu, Au)₃Sn₄ phases increased and the intermetallic compounds (IMCs) growth mechanism obeyed the parabolic law and the IMC growth mechanism was diffusion-controlled. The mechanical strengths for both the soldered joints decreased with increasing thermal aging time. The SACNG/Au/Ni/Cu couple had better mechanical strength than that in the SAC/Au/Ni/Cu couple.     

Wetting and interfacial reaction characteristics of Sn-1.2Ag-0.5Cu-xIn quaternary solder alloys

Through the use of a wetting balance technique, the wetting characteristics of Sn-1.2Ag-0.5Cu-xIn quaternary solder alloys with respect to the In content and soldering temperature were investigated to validate the applicability of compositions with a low Ag content as solder material. It was found that a small addition (0.4–0.6 wt.%) of In significantly improved the wetting properties of the Sn-1.2Ag-0.5Cu-xIn composition at soldering temperatures ranging from 230 °C to 240 °C due to the excellent wetting property of In. In an observation of the interfacial reaction, it was found that the added In element did not participate in the interfacial reaction with a Cu or Ni pad, unlike in the Sn-Ag-Cu-In case, which has a high In content. The package or boardside IMC layers in Sn-1.2Ag-0.5Cu-0.4In joints were thinner than those of Sn-3.0Ag-0.5Cu, especially after aging.     

Sn-3.0Ag-0.5Cu-XCo钎焊接头金属间化合物层电迁移现象的研究

研究了以Co颗粒为增强相的Sn3.0Ag0.5Cu钎料合金接头的电迁移特性。结果表明,50℃、104A/cm2条件下直至16d,Sn3.0Ag0.5Cu-0.2Co钎料接头无明显电迁移现象产生。将温度提高至150℃后,接头正、负极处金属间化合物(IMC)层的厚度产生明显差异,即电子风力引发的‘极化效应’。Sn3.0Ag0.5Cu钎料接头在通电1d和3d后,正、负极处IMC层的结构发生了相反的变化。而Sn3.0Ag0.5Cu-0.05Co接头在通电3d后,负极处产生明显裂纹。此外,Co的引入有效地缓解了IMC层的生长趋势,提高了接头显微组织的稳定性。     

Sn-3.5Ag-0.5Cu/Cu界面的显微结构

研究了热-剪切循环条件下Sn-3．5Ag-0．5Cu钎料／Cu界面的显微结构，分析了界面金属间化合物的生长行为，并与恒温时效后的Sn-3．5Ag-0．5Cu／Cu界面进行了对比。结果表明：恒温时效至100h，Sn-3．5Ag-0．5Cu／Cu界面上已形成Cu6Sn5和Cu3Sn两层金属间化合物；而热-剪切循环至720周Sn-3．5Ag-0．5Cu／Cu界面上只存在Cu6Sn5金属间化合物层，无Cu3Sn层生成，在界面近域的钎料内，颗粒状的Ag3Sn聚集长大成块状；在热-剪切循环和恒温时效过程中，界面金属间化合物的形态初始都为扇贝状，随着时效时间的延长逐渐趋于平缓，最终以层状形式生长。     

多场耦合条件下SnAgCu/Cu界面化合物生长行为

基于自制的多场耦合热循环装置,研究了Sn-3.0Ag-0.5Cu/Cu钎焊接头热循环过程中界面金属间化合物(IMC)微观组织变化和断裂行为. 结果表明,在多场耦合及30~150 ℃热疲劳循环下,随着循环周期的增加,界面IMC厚度越来越厚,且在较短循环时间内IMC的形貌由扇贝状转变为层状,400周期后界面化合物的厚度增长变缓;当循环周期达到600时,界面上空洞聚集长大,产生界面开裂,进而导致疲劳失效. 同时随着循环周期增加,接头的抗剪强度也逐渐下降,也有脆性断裂的趋势.     

Improving the shear strength of Sn–Ag–Cu–Ni/Cu–Zn solder joints via modifying the microstructure and phase stability of Cu–Sn intermetallic compounds

This study focuses on the correlation between high-speed impact tests and the interfacial reaction in Sn-3.0Ag-0.5Cu-0.1Ni/Cu (wt%) and Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints. Adding Ni into the Sn–Ag–Cu solder alters the interfacial morphology from scallop type to layer type and exhibits high shear strength after reflow in both solder joints. However, the shear strength of Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints degrades significantly after thermal aging at 150 °C for 500 h. It is notable that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints still present higher shear strength after aging at 150 °C. The weakened shear strength in Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints is due to stress accumulation in the interfacial (Cu,Ni)₆Sn₅ compound induced by the phase transformation from a high-temperature hexagonal structure (η-Cu₆Sn₅) to a low-temperature monoclinic structure (η'-Cu₆Sn₅). However, doping small amounts of Zn into (Cu,Ni)₆(Sn,Zn)₅ can inhibit the phase transformation during thermal aging and maintain strong shear strength. These experiments demonstrate that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints can act as a stable connection in the micro-electronic packaging of most electronic products at their average working temperatures.     

Sn-6.5Zn/Cu焊点时效过程中的界面特征与结构演变

研究150°C等温时效对Sn-6.5Zn/Cu焊点微观结构特征与显微硬度的影响,分析界面金属间化合物的形成与演变机制。结果表明：Sn-6.5Zn/Cu焊点界面化合物层由CuZn和Cu5Zn8组成;随着等温时效时间的延长,化合物层的厚度表现为先增大、后减小的趋势;长时间的高温时效会导致Cu-Zn金属间化合物的分解,并破坏界面连续致密的化合物层。在局部破坏的界面区Cu基体处形成不连续的Cu6Sn5化合物层;时效后界面粗化并形成明显的孔洞。时效导致界面显微硬度不同程度的增大。     

等温时效对SnAgCu焊点界面组织及剪切强度的影响

研究了Sn-3.0Ag-0.5Cu/Cu焊点分别在1、5、10min焊接时间后在373、403、438K时效温度下焊点界面IMC的生长和剪切强度随时效时间的变化,同时对焊点断口形貌及断裂模式进行了分析。结果表明,焊接时间越长,界面IMC层越厚。随着时效时间的延长,界面IMC不断增厚,其生长动力学符合抛物线生长规律,生长激活能为75.03kJ/mol;焊点剪切强度随时效时间增加不断下降,其断裂方式从开始的韧性断裂逐渐转变为局部脆性断裂。     

不同应变速率下BGA焊球剪切断裂试验与模拟分析

研究了BGA封装Sn-3.0Ag-0.5Cu无铅焊球经115℃时效后,焊球/铜界面IMC的形貌和组织变化,同时对BGA焊球在两种不同应变速率条件下的抗剪强度进行了分析,并运用ANSYS12.0软件对其过程进行2-D非线性有限元模拟.试验结果表明,随着时效时间的延长,界面形貌由时效前的树枝状变成连续平坦的层状、界面IMC不断增厚,且焊球的抗剪强度随着时效时间的增加而不断降低;应变速率越高,抗剪强度越高.模拟结果表明,应变速率越高,焊球经受的抗剪强度越大,Von Mises应力越大,等效塑性应变越小,塑性应变能密度越大.     

Ti90及其优化合金的组织与力学性能研究

研究了钎焊与时效过程中,在Sn0.7Ag0.5Cu(SAC0705)钎料与Cu基板和石墨烯Cu基板界面处金属间化合物(IMC)的形成与演变。采用加热平台制备焊接试样并在120℃时效600h。结果表明,界面金属间化合物在时效过程中增厚。SAC0705/Cu和SAC0705/G-Cu 2种焊接界面金属间化合物均为Cu6Sn5。当钎料中添加Ni元素后,Cu6Sn5化合物转变为(Cu,Ni)6Sn5。随着钎料中Ni元素含量的增大,2种基板上的界面金属间化合物厚度先增加后减小。此外,随着Ni含量增大,化合物生长速率降低。石墨烯Cu基板表面的石墨烯层起到扩散阻挡层效果,因此,石墨烯Cu板上的化合物厚度小于常规Cu基板,同时其界面化合物生长速率较低。     

Ni和Bi元素对SnAgCu钎焊界面金属化合物生长速率的影响

通过加速温度时效方法研究Ni和Bi元素对低银(含银量小于1%,质量分数)Sn-Ag-Cu(LASAC)钎料界面IMC生长速率的影响。通过与高银钎料SAC305和低银钎料LASAC对比,分析添加Ni和Bi元素后LASAC钎料在高温时效过程中热疲劳抗性的变化情况。结果表明:LASAC/Cu、LASAC-Bi/Cu和SAC305/Cu界面IMC时效后均形成较厚的Cu3Sn层,LASAC-Ni/Cu界面经IMC时效后则形成较薄的(Cu,Ni)3Sn;高银钎料SAC305在180℃时效下IMC生长速率为2.17×10-5μm2/s,与之相比,低Ag钎料LASAC IMC在时效过程中生长速率较高,为3.8×10-5μm2/s;Ni和Bi元素的添加均可降低钎料LASAC/Cu界面IMC的生长速率,其中Bi的改善效果最显著,LASAC-Bi钎料的IMC生长速率为1.92×10-5μm2/s,低于SAC305钎料的IMC生长速率。     

钎焊时间对镀镍SiCP/Al复合材料界面IMC生长的影响

采用Sn-3.0Ag-0.5Cu-3.0Bi钎料对镀镍60%和镀镍15% SiC_P/6063Al复合材料之间进行真空钎焊.采用SEM,XRD对接头界面微观组织和成分进行分析.结果表明,在钎焊过程中,钎料与镍层发生界面反应生成了连续的扇贝状金属间化合物（IMC）,其具体成分为（Cu,Ni）₆Sn₅;该IMC层排列紧凑,生长方向都垂直于界面指向钎料的内部;在钎焊过程中,IMC的生长分为生长速率较快和生长速率较缓慢两个阶段.在270℃,钎焊时间由10 min延长至40 min时,界面IMC层扇贝状形貌不变,晶粒尺寸变大;IMC层厚度增加,但是其厚度增长速率逐渐降低;钎焊接头抗剪强度不断增大.     

SAC0307-xNi/Ni焊点的IMC及镍镀层的消耗

利用扫描电镜(SEM)对焊点SAC0307/Ni(Sn-O.3Ag-0.7Cu/Ni)和SAC0307-0.05Ni/Nj(Sn-O.3Ag-0.7Cu-0.05 Ni/Ni)经过180℃老化后的界面金属问化合物(IMC)的微观结构及镍镀层的消耗进行了研究.结果表明,回流焊后,SAC0307/Ni和SAC0307-O.05Ni/Ni焊点的IMC层均为(Cu_(1-x)Ni_x)_6Sn_5,且随着老化时间的延长,IMC层的厚度均逐渐增加,化合物类型没有变化,但IMC的化学组成有所改变.SAC0307-0.05Ni/Ni焊点中IMC层形貌为蠕虫状,厚度比不加镍时有所降低.回流焊后两种钎料焊盘的镍层消耗几乎相同,但老化384h后SAC0307/Ni的焊盘镍层的剩余厚度明显比SAC0307-0.05Ni/Ni的小.因此,钎料中添加适量的镍可以有效地降低焊盘镍层在时效过程中的消耗速率,即显著提高镍焊盘的抗老化能力.

Abstract：

The micrestmcture of interfacial IMC and the consumption of Ni layer for SAC0307/Ni ( Sn-0.3Ag-0.7Cu/Ni ) soldered joint and SAOY307-0.05Ni/Ni (Sn-O. 3Ag-0.7Cu-0.05Ni/Ni) soldered joint after aging at 180℃ were studied by scanning electron microscope( SEM ). The results indicated that the IMC layer of SAC0307/Ni and SAC0307-0.05Ni/Ni are both (Cu_(1-x),Ni_x)_6Sn_5 after reflow soldering. With the increasing of aging time, the thickness of IMC layer increases gradually, the type of IMC is not changed, but the chemical composition changes. The morphology of IMC is stormshaped and the thickness of IMC is much thinner when SAC0307 solder added 0. 05 % Ni is used. The consumption of Ni layer is nearly the same using both solders "after the first time reflow soldering, but the residual thickness of the Ni layer in SACO307/Ni solder is thinner than that in SAC0307-0.05Ni/Ni after aging for 384 h. So solders with a little Ni element can decrease the consumption rate of Ni layer effectively during aging, that is, the aging-resistant abihty of Ni pad is improved obviously.     

Effect of rare earth metal Ce addition to Sn-Ag solder on interfacial reactions with Cu substrate

The effect of adding a small amount of rare earth cerium (Ce) element to low Ag containing Sn-1wt%Ag Pb-free solder on its interfacial reactions with Cu substrate was investigated. The growth of intermetallic compounds (IMCs) between three Sn-1Ag-xCe solders with different Ce contents and a Cu substrate was studied and the results were compared to those obtained for the Ce-free Sn-1Ag/Cu systems. In the solid-state reactions of the Sn-1Ag(-xCe)/Cu solder joints, the two IMC layers, Cu₆Sn₅ and Cu₃Sn, grew as aging time increased. Compared to the Sn-1Ag/Cu joint, the growth of the Cu₆Sn₅ and Cu₃Sn layers was depressed for the Ce-containing Sn-1Ag-xCe/Cu joint. The addition of Ce to the Sn-Ag solder reduced the growth of the interfacial Cu-Sn IMCs and prevented the IMCs from spalling from the interface. The evenly-distributed Ce elements in the solder region blocked the diffusion of Sn atoms to the interface and retarded the growth of the interfacial IMC layer.     

微连接用Sn-2.5Ag-0.7Cu(0.1RE)钎料焊点界面Cu6Sn5的长大行为

利用XRD、SEM及EDAX研究了钎焊和时效过程中低银Sn-2.5Ag-0.7Cu(0.1RE)/Cu焊点界面区显微组织和Cu6Sn5金属间化合物的生长行为。结果表明,钎焊过程中焊点界面区Cu6Sn5金属间化合物的厚度是溶解和生长两方面共同作用的结果;随时效时间的增加,焊点界面区Cu6Sn5的形貌由扇贝状转变为层状,其长大动力学符合抛物线规律,由扩散机制控制;添加0.1%(质量分数,下同)的RE能有效减慢界面Cu6Sn5金属间化合物在钎焊及时效过程中的长大速度,改变焊点的断裂机制,提高其可靠性。     

Pr,Nd对Sn0.3Ag0.7Cu0.5Ga无铅钎料显微组织的影响

分析了添加两种稀土元素Pr,Nd对Sn-0.3Ag-0.7Cu-0.5Ga无铅钎料基体组织、焊点界面组织的影响并测定了焊点抗剪强度.结果表明,在该钎料中分别添加Pr,Nd元素可以改善钎料的显微组织,且加入Pr元素的效果优于Nd.添加Pr元素的钎料基体组织中金属间化合物分布均匀,而后者易在晶界处产生“区域”状金属间化合物,成为裂纹的发源地.稀土元素的吸附作用可以降低钎料与铜基板界面反应的剧烈程度,从而改善界面的形貌.添加Pr元素的钎料可以更好地与铜基板结合,从而提高了焊点的抗剪强度.