等温时效对SnCuTi/Cu无铅焊点界面反应及力学性能的影响

研究了在125℃时效过程中,Sn-0.7Cu-0.008Ti/Cu焊点界面IMC的生长及抗剪强度的变化。结果表明,Sn-0.7Cu-0.008Ti/Cu焊点界面IMC厚度在时效过程中不断增加,并且与时效时间呈抛物线函数关系;界面IMC形貌由扇贝状转变为波浪状,相组成由单一的Cu6Sn5相转变为Cu6Sn5+Cu3Sn的分层组织。相同时效条件下,钎焊间隙对界面IMC的生长影响不大。焊点的抗剪强度随时效时间的增加而逐渐降低,但微量Ti的加入可明显改善焊点的力学性能。     

时效对Sn-0.7Cu-0.05Ni-xSm/Cu焊点界面与抗剪强度的影响

以Sn-0.7Cu-0.05Ni-xSm/Cu焊点为对象(元素Sm含量分别为0,0.025,0.05,0.1和0.2(质量分数,%)),研究焊后与经过160 ℃,24,96和360 h时效后,焊点界面金属间化合物(IMC)与抗剪强度的变化. 结果表明,在钎料中未添加稀土元素Sm时,IMC层凹凸不平;加入微量元素Sm,IMC层变的平坦顺滑. 时效会使IMC不断长大,其界面形貌由原始的扇贝状向平直均匀的层状转变. 元素Sm含量在0.025%～0.1%范围内时,不论时效前还是时效后,IMC层较薄. 元素Sm对界面IMC的生长有抑制作用,有益于提高焊点的可靠性. 加入微量稀土元素Sm以后,焊点抗剪强度发生了变化. 不论时效前还是时效后,当元素Sm含量为0.025%时,焊点抗剪强度都是最高.     

矩形片式电阻半导体激光钎焊无铅焊点的热循环试验

选用Sn-Ag-Cu无铅钎料,采用半导体激光软钎焊和红外再流焊两种方法对0805型矩形片式电阻元件进行钎焊,并对采用不同方法得到的钎焊焊点进行热循环试验.结果表明,激光软钎焊矩形片式电阻焊点的力学性能优于传统红外再流焊工艺所获得的电阻焊点的力学性能;片式电阻焊点的剪切力随热循环次数的增加呈现下降趋势,在热循环次数相同时,激光软钎焊焊点的力学性能优于红外再流焊焊点.随着热循环次数的增加,片式电阻焊点的剪切断裂的方式由明显的韧性断裂逐渐向脆性断裂转变.     

稀土元素Nd对Sn3．8AgO．7Cu焊点组织与抗剪强度的影响

研究了微量稀土元素Nd（0,0．05,0．5质量分数,％）的添加对Sn3．8Ag0．7Cu／cu焊点再流焊与150℃时效条件下焊点组织与抗剪强度的影响．结果表明,适量Nd（0．05％）的添加可以明显增强微焊点的抗剪强度,改善焊点组织;降低时效过程中SnAgCu／Cu焊点界面化合物生长速率以及焊点内部基体中Cu6Sn5化合物的颗粒粗化速率,从而有利于提高微焊点长期服役过程中的可靠性．时效过程中,SAC-0．05Nd焊点力学性能下降速率较SAC焊点有所降低,而SAC-0．5Nd焊点由于稀土化合物NdSn,相的粗化,与SAC微焊点力学性能下降速率无明显差异．     

时效对BGA无铅焊点抗剪强度和断裂模式的影响

测试了BGA(球栅阵列)板级封装Sn-3.0Ag-0.5Cu焊点经时效后的抗剪强度,并采用三维超景深显微镜对全部试样焊点的断裂模式进行统计分析。对比研究不同时效温度、时效时间和焊盘处理方式(OSP,Ni/Pd/Au)对焊点抗剪强度及断裂模式的影响。试验结果表明:时效温度越高,时间越长,焊点的抗剪强度越低,在相同时效条件下,焊盘经Ni/Pd/Au处理的焊点抗剪强度高于经OSP处理的焊点抗剪强度;断裂模式随时效温度的升高和时间的延长,由焊球断裂向界面开裂及焊盘失效转变。     

矩形片式电阻元件的半导体激光软钎焊技术

采用Sn-Ag-Cu作为钎焊材料,研究了矩形片式电阻元件的半导体激光软钎焊技术,采用微焊点强度测试仪研究了其力学性能.结果表明,当激光钎焊时间固定时,随着激光输出功率的增加,电阻焊点的剪切力呈现增加的趋势,在某一功率左右达到最大值.随着激光钎焊时间的增加,其所对应的最佳激光输出功率逐渐减小,最佳的激光钎焊时间为1s.对比试验结果表明,激光软钎焊的最佳工艺参数组合所得到的片式电阻焊点力学性能优于采用传统红外再流焊工艺所获得的片式电阻焊点的力学性能.     

SnCuNi-xPr/Cu界面组织和性能分析

分析了稀土元素Pr及其两种添加量对Sn0.7Cu0.05Ni无铅钎料焊点界面组织和性能的影响,并对其影响机制进行了初步探讨.结果表明,Pr元素的加入明显改善了钎料/基板的界面组织形貌,使其更为均匀平坦.Pr元素可通过减小界面反应化学驱动力,缩短反应时间,并与Ni元素产生"协同作用"来控制界面反应的进行;稀土元素Pr可通过PrSn3相颗粒的析出对焊点组织起到第二相强化的作用,同时会阻碍晶界或相界迁移以细化晶粒,提高焊点强度和韧性,对钎料焊点抗剪强度的测试验证了该理论.     

时效对SnAgCu/SnAgCu-TiO2焊点界面与性能影响

研究了SnAgCu与SnAgCu-TiO2两种无铅钎料与铜基板之间的界面反应,研究其在140℃时效过程中的生长行为及力学性能变化.结果表明,焊后两种钎料对应界面层为Cu6Sn5相,经过140℃时效,界面层厚度随着时效时间的增加而增加.发现金属间化合物层厚度和时效时间的平方根成正比例关系.当时效时间为300 h时,界面层出现Cu3Sn相,发现纳米TiO2颗粒对界面金属间化合物层厚度有明显的抑制作用.同时对焊点力学性能分析,在时效过程中焊点平均拉伸力明显下降,SnAgCu-TiO2焊点的力学性能明显优于SnAgCu焊点.     

SnAgCu无铅微焊点剪切力学性能的体积效应

对直径200～600 μm的Sn3.OAg0.5Cu无铅微焊点进行了多次重熔及老化试验,并采用专业的微小焊点力学性能测试仪DAGE4000测试了焊点的抗剪强度,分析了焊点体积差异对焊点抗剪强度的影响,发现SnAgCu无铅焊点的抗剪强度随着焊点体积增大呈下降趋势,体现出明显的体积效应.讨论了老化时间及重熔次数对不同体积焊...     

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.     

Nd对Sn-0.7Cu-0.05Ni焊点组织与力学性能的影响

研究了添加微量稀土元素Nd对Sn-0.7Cu-0.05Ni/Cu无铅焊点再流焊和150 ℃时效条件下焊点界面组织与力学性能的影响. 结果表明,添加适量Nd(质量分数为0.06%)可以优化焊点界面组织,减缓时效过程中Sn-0.7Cu-0.05Ni/Cu界面化合物的生长速率,提高焊点力学性能,增强焊点的可靠性. 时效过程中,添加了0.06%Nd的Sn-0.7Cu-0.05Ni钎料焊点的剪切力始终保持最大,在时效1 440 h后,Sn-0.7Cu-0.05Ni-0.06Nd/Cu焊点的剪切力相比未添加稀土的Sn-0.7Cu-0.05Ni钎料提高了31.9%.     

Nd对Sn-3.8Ag-0.7Cu/Cu焊点高温可靠性的影响

通过研究150 ℃时效条件下Sn-3.8Ag-0.7Cu-0.05Nd/Cu焊点剪切力变化和界面微观结构演变,探讨稀土元素Nd对焊点高温可靠性的影响及其影响机制. 结果表明,不同时效时间后Sn-3.8Ag-0.7Cu-0.05Nd/Cu焊点剪切力明显高于Sn-3.8Ag-0.7Cu/Cu焊点,且时效过程中Sn-3.8Ag-0.7Cu-0.05Nd/Cu焊点剪切力的下降速率低于原焊点. 这是由于0.05%Nd可将界面原子扩散系数由1.88 × 10?10 cm2/h降低至1.10 × 10?10 cm2/h,即通过抑制界面金属间化合物的粗化来提高焊点的高温可靠性.     

Interfacial microstructure and properties of Sn-0.7Cu-0.05Ni/Cu solder joint with rare earth Nd addition

Interfacial microstructure and properties of Sn-0.7Cu-0.05Ni/Cu solder joints with trace amounts Nd additions have been investigated in this paper. The evolution of interfacial morphology of SCN solder joints with and without the presence of Nd under long-term room ambience was also studied. The greatest improvement to the solderability and tensile strength of SCN-xNd are obtained at 0.05 wt.% Nd. Meanwhile, the morphology and growth of interfacial intermetallic (IMC) layer are greatly improved by adding Nd, and the propensity for IMC spalling from the interface of solder joint is definitely reduced with the presence of rare earth Nd, since the sponge-like structure was completely inhibited in the solder joint containing Nd. In addition, a significant amount of Sn whiskers were present on the surface of NdSn₃ phases in the SCN0.15Nd/Cu solder joints, and the reason for this phenomenon has been briefly discussed.     

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.     

Ni segregation in the interfacial (Cu,Ni)6Sn5 intermetallic layer of Sn-0.7Cu-0.05Ni/Cu ball grid array (BGA) joints

Ni segregation in the interfacial (Cu,Ni)₆Sn₅ intermetallic layer of Sn-0.7Cu-0.05Ni/Cu BGA solder joints was investigated by using synchrotron micro X-ray fluorescence (XRF) analysis and synchrotron X-ray diffraction (XRD). Compared to Sn-0.7Cu/Cu BGA joints, Ni containing solder show suppressed Cu₃Sn growth in both reflow and annealed conditions. In as-reflowed Sn-0.7Cu-0.05Ni/Cu BGA joints, Ni was relatively homogenously distributed within interfacial (Cu,Ni)₆Sn₅. During subsequent annealing, the diffusion of Ni in Cu₆Sn₅ was limited and it remained concentrated adjacent the Cu substrate where it contributes to the suppression of Cu₃Sn formation at the interface between the Cu substrate and Cu₆Sn₅ intermetallics.     

Sn-0.3Ag-0.7Cu-xNd钎料显微组织及性能

研究了稀土元素Nd的添加量对超低银无铅钎料Sn-0.3Ag-0.7Cu的润湿性能、显微组织和力学性能的影响.结果表明,微量Nd元素的加入可以显著改善Sn-0.3Ag-0.7Cu超低银无铅钎料的润湿性能和焊点的力学性能,并且能够起到细化基体组织的作用.当钎料中Nd元素的质量分数达到0.1%时,钎料的综合性能最佳,基体组织最为均匀细化.虽然Ag元素含量的降低使钎料的性能有所下降,但是加入适量Nd元素后钎料的润湿性能已接近传统Sn-3.8Ag-0.7Cu钎料.     

Development of high strength Sn-0.7Cu solders with the addition of small amount of Ag and In

Nowadays, a major concern of Sn-Cu based solder alloys is focused on continuously improving the comprehensive properties of solder joints formed between the solders and substrates. In this study, the influence of Ag and/or In doping on the microstructures and tensile properties of eutectic Sn-0.7Cu lead free solder alloy have been investigated. Also, the effects of temperature and strain rate on the mechanical performance of Sn-0.7Cu, Sn-0.7Cu-2Ag, Sn-0.7Cu-2In and Sn-0.7Cu-2Ag-2In solders were investigated. The tensile tests showed that while the ultimate tensile strength (UTS) and yield stress (YS) increased with increasing strain rate, they decreased with increasing temperature, showing strong strain rate and temperature dependence. The results also revealed that with the addition of Ag and In into Sn-0.7Cu, significant improvement in YS (∼255%) and UTS (∼215%) is realized when compared with the other commercially available Sn-0.7 wt. % Cu solder alloys. Furthermore, the Sn-0.7Cu-2Ag-2In solder material developed here also exhibits higher ductility and well-behaved mechanical performance than that of eutectic Sn-0.7Cu commercial solder. Microstructural analysis revealed that the origin of change in mechanical properties is attributed to smaller β-Sn dendrite grain dimensions and formation of new inter-metallic compounds (IMCs) in the ternary and quaternary alloys.     

BGA单板结构与板级结构焊点剪切力学行为分析

采用试验方法研究BGA封装结构中焊点的剪切力学行为. 分析并比较了Sn-3Ag-0.5Cu,Sn-0.3Ag-0.7Cu,Sn-0.3Ag-0.7Cu-0.07La和Sn-0.3Ag-0.7Cu-0.07La-0.05Ce四种钎料焊点在单板结构与板级结构中的力学性能. 结果表明, 单板结构中焊点的抗剪强度高于板级结构中焊点的抗剪强度. 在单板结构中,高银焊点的抗剪强度最大,加入稀土元素的低银焊点只是得到了一定程度上的改善,然而对于板级结构,加入稀土元素的低银焊点剪切力学性能基本与高银焊点相当. 在同等拘束条件下,低银焊点的延展性优于高银焊点. 此外,对于同一种钎料而言,单板结构中的焊点断裂在体钎料上,而板级结构则断裂在IMC/体钎料界面处.     

Pb-free solders for flip-chip interconnects

A variety of lead-free solder alloys were studied for use as flip-chip interconnects including Sn-3.5Ag, Sn-0.7Cu, Sn-3.8Ag-0.7Cu, and eutectic Sn-37Pb as a baseline. The reaction behavior and reliability of these solders were determined in a flip-chip configuration using a variety of under-bump metallurgies (TiW/Cu, electrolytic nickel, and electroless Ni-P/Au). The solder micro-structure and intermetallic reaction products and kinetics were determined. The Sn-0.7Cu solder has a large grain structure and the Sn-3.5Ag and Sn-3.8Ag-0.7Cu have a fine lamellar two-phase structure of tin and Ag₃Sn. The intermetallic compounds were similar for all the lead-free alloys. On Ni, Ni₃Sn₄ formed and on copper, Cu₆Sn₅Cu₃Sn formed. During reflow, the intermetallic growth rate was faster for the lead-free alloys, compared to eutectic tin-lead. In solidstate aging, however, the interfacial intermetallic compounds grew faster with the tinlead solder than for the lead-free alloys. The reliability tests performed included shear strength and thermomechanical fatigue. The lower strength Sn-0.7Cu alloy also had the best thermomechanical fatigue behavior. Failures occurred near the solder/intermetallic interface for all the alloys except Sn-0.7Cu, which deformed by grain sliding and failed in the center of the joint. Based on this study, the optimal solder alloy for flip-chip applications is identified as eutectic Sn-0.7Cu. Editor’s Note: A hypertext-enhanced version of this article can be found at www.tms.org/pubs/journals/JOM/0106/Frear-0106.html For more information, contact D.R. Frear, Interconnect Systems Laboratories, Motorola, Tempe, AZ 85284; (480) 413-6655; fax (480) 413-4511; e-mail darrel.frear@motorola.com.     

Interfacial Reactions and Bonding Strength of Sn-xAg-0.5Cu/Ni BGA Solder Joints

The present study details the microstructure evolution of the interfacial intermetallic compounds (IMCs) layer formed between the Sn-xAg-0.5Cu (x = 1, 3, and 4 wt.%) solder balls and electroless Ni-P layer, and their bond strength variation during aging. The interfacial IMCs layer in the as-reflowed specimens was only (Cu,Ni)₆Sn₅ for Sn-xAg-0.5Cu solders. The (Ni,Cu)₃Sn₄ IMCs layer formed when Sn-4Ag-0.5Cu and Sn-3Ag-0.5Cu solders were used as aging time increased. However, only (Cu,Ni)₆Sn₅ IMCs formed in Sn-1Ag-0.5Cu solders, when the aging time was extended beyond 1500 h. Two factors are expected to influence bond strength and fracture modes. One of the factors is that the interfacial (Ni,Cu)₃Sn₄ IMCs formed at the interface and the fact that fracture occurs along the interface. The other factor is Ag₃Sn IMCs coarsening in the solder matrix, and fracture reveals the ductility of the solder balls. The above analysis indicates that during aging, the formation of interfacial (Ni,Cu)₃Sn₄ IMCs layers strongly influences the pull strength and the fracture behavior of a solder joint. This fact demonstrates that interfacial layers are key to understanding the changes in bonding strength. Additionally, comparison of the bond strength with various Sn-Ag-Cu lead-free solders for various Ag contents show that the Sn-1Ag-0.5Cu solder joint is not sensitive to extended aging time.