Sn-Ag基无铅钎料Nd:YAG激光重熔界面研究

通过Nd∶YAG激光重熔和热风二次重熔试验,得到了Sn3.5Ag和Sn3.0Ag0.5Cu无铅钎料球在Cu焊盘的钎料凸台.利用扫描电子显微镜分别分析了激光重熔和热风二次重熔后两种无铅钎料与铜焊盘界面反应及组织形貌,并对激光一次重熔无铅钎料凸台进行了剪切试验,观察了凸台的剪切断口.结果表明,在合适的激光功率和加热时间条件下能够获得成形良好的无铅钎料凸台,Sn3.5Ag和Sn3.0Ag0.5Cu两种无铅钎料与Cu焊盘所产生的界面化合物主要为Cu3Sn和Cu6Sn5,凸台界面反应组织形貌以及剪切承载力与激光功率和加热时间密切相关,而且激光重熔形成的界面化合物影响热风二次重熔界面的组织形貌.     

Sn3．5Ag0．7Cu焊料的疲劳特性及铅杂质的影响

含铅焊料应用在电子产品上已超过50年的时间。然而出于环境方面的考虑，在未来的几年含铅焊料的使用将被禁止。作为替代，必须发明不含铅的焊料。对无铅焊料总的要求类似于含铅焊料。它们要求类似的诸如焊接温度及时间工艺参数窗口和相当于含铅焊料或更好的特性。科学家们已研究了许多不同类型的无铅焊料，从中我们选取Sn3、5Ag0．7Cu作为本次研究的对象，因为它可能目前是在欧洲应用最广泛的一种无铅合金。通过下面几项工作中我们研究了Sn3．5Ag0.7Cu的疲劳特性。制成板(PCBA)温度循环(热冲击)试验：用Sn3．5Ag0．7Cu无铅焊料在不同的焊接气氛下将各种不同类型的器件焊在有不同可焊性表面覆层的印制板上，做成试验制成板(PCBA)。将125℃到-15℃的温度循环(热冲击)施与试验制成板并研究板上焊点在经受不同次数的温度循环后其微观组织结构及变化。模型焊点的机械应力循环试验：室温条件下利用特别设计的环一插针模型焊点，Sn3．5Ag0．7Cu无铅焊点被施加机械应力循环并和传统的Sn-Pb焊点进行比较。包含不同铅含量的焊点也被研究以确认铅杂质对无铅焊点特性的影响。比起传统的Sn-Pb焊料，Sn3．5Ag0．7Cu有更好的疲劳特性。然而研究同时发现一个2％-5％的铅杂质含量对无铅焊点的寿命是有害的。     

Sn-Ag-Cu和Sn-Pb焊球及锡膏混合焊点的组织结构

在从含铅制程到无铅制程的转换过程中会遇到四种不同的焊点冶金组合：无铅焊料和无铅元件；无铅焊料和含铅元件；锡铅焊料和无铅元件;锡铅焊料和含铅元件。为了更好的优化工艺参数并获得高可靠性的焊点，我们必须研究上述不同冶金组合焊点的冶金过程和组织特性。本研究工作中，Sn-3．8Ag-0．7Cu、Sn-37Pb两种BGA焊球和Sn-3．8Ag-0．7Cu、Sn-37Pb两种锡膏分别组合焊接在表面无电解镀镍／浸金(Ni／Au)的试验板上，得到四种不同冶金组合的焊点。部分制成的试验板叉分别经过150℃310小时、480小时、2160d小时的老化。对上述焊点分别进行剪切力测试并使用X-射线透视．仪、光学显微镜、扫描电子显微镜、散射X-射线光谱仪等试验设备对焊点进行检测。对部分未经过老化的焊点用差示扫描量热法进行了分析。我们着重对四种不同冶金组合的焊点的微观结构及组织构成、金属间化合物构成、表面粗糙度以及焊点空洞问题进行了研究，并对四种不同冶金组合的焊点的相似处和不同处进行了讨论。研究揭示了焊点微观组织结构对焊点剪切强度和断裂模式的影响。     

Sn-Ag-Cu无铅焊料性能研究

环保和微电子器件高度集成化的发展驱动了高性能无铅焊料的研究和开发,Sn—Ag－Cu系无铅焊料由于具有良好的焊接性能和使用性能,已逐渐成为一种通用电子无铅焊料。文章通过实验的方法,研究了8种不同配比的Sn—Ag—Cu焊料中银、铜含量对合金性能（包括熔点、润湿性和剪切强度）的影响,并对焊料的显微组织进行对比与分析,得出低银焊料的可靠性比高银焊料好,同时Sn－2．9Ag—1．2Cu的合金具有较低的熔点且铺展性好,为确定综合性能最佳的该系焊料合金提供了依据。     

FeNi合金UBM圆片级封装焊点剪切力研究

FeNi合金与无铅焊料反应速率低,生成的金属间化合物(IMC)较薄,有望作为圆片级封装(WLP)凸点下金属(UBM)层材料.对两种FeNi UBM以及一种Cu UBM圆片级封装样品进行回流、湿热以及预处理实验,并通过推球的方法,对其焊点进行剪切测试.通过断面与截面分析,研究其在不同处理条件下的金属间化合物生长情况,分析其断裂模式.结果表明,FeNi UBM焊点剪切力高于Cu UBM.Fe47Ni UBM与焊料反应生成的金属间化合物较薄,对于剪切力影响较小,而Fe64Ni UBM与焊料反应生成离散的CuNiSn金属间化合物,对于其焊点强度有提高作用,Cu UBM与焊料反应生成较厚的金属间化合物,会明显降低焊点的剪切力.断面分析表明,Cu UBM会随焊球发生断裂,其强度明显小于FeNi UBM.     

微电子封装中Sn—Aq—Cu焊点剪切强度研究

提出了一种对微电子封装器件中焊点剪切强度进行测试的方法，可有效降低测试误差。利用该方法，对Sn—Ag—Cu无铅焊料分别在Cu基板和Ni-P基板上形成的焊点，经不同的热时效后的剪切强度进行了测量，并对断裂面的微观结构进行了研究。结果表明，新的剪切测试方法误差小，易于实施，焊点剪切强度、断裂面位置与焊料在不同基板界面上金属间化合物的形貌、成分有关。     

微量Co对低银无铅焊料润湿及界面反应的影响

利用润湿测量仪研究了加入微量Co对低银无铅焊料Sn1.00Ag0.70Cu和Sn0.50Ag0.70Cu润湿性能的影响,并与共晶无铅焊料Sn3.00Ag0.50Cu的润湿性能进行对比。结果发现,焊料Sn3.00Ag0.50Cu、Sn1.00Ag0.70Cu0.07Co和Sn0.50Ag0.70Cu0.03Co的润湿平衡力F分别为3.0850,3.0600和3.0275mN,润湿时间分别为0.64,0.88和1.01s。低银微钴无铅焊料显示了与共晶无铅焊料类似的润湿力,只是润湿时间略有增加。     

电子组装用高温无铅钎料的研制

Bi-Ag合金是一种替代高铅钎料的芯片封装无铅焊料。研制了Bi-2.5Ag、Bi-2.5Ag-0.1RE、Bi-5Ag-0.1RE、Bi-7.5Ag-0.1RE、Bi-10Ag、Bi-10Ag-0.1RE钎料。结果表明,该合金系钎料的熔化温度范围随Ag含量的增加而增大,而且其润湿性能良好,润湿角都处于30o～40o。不同Ag含量的Bi-Ag/Cu接头在界面处发生断裂,剪切强度差别不大,都略大于30MPa。Bi-Ag/Cu界面没有金属间化合物形成,结合强度较弱。     

Sn-Ag-Cu焊料中金属间化合物对焊接性能的影响

讨论了Sn-Ag-Cu焊料与Cu焊盘间在回流焊过程中形成的金属间化合物(IMC)的种类、形态,Ag含量和Cu含量对IMC的影响,IMC在老化过程中的生长演变及其对焊接性能的影响。结果表明:Sn-Ag-Cu焊料与Cu焊盘之间的金属间化合物主要是Cu6Sn5和长针状的Ag3Sn,Ag和Cu的添加对组织有明显细化作用,但过量添加会影响IMC的性能。IMC的演变主要是与老化温度、老化时间有关,较厚的IMC不利于焊接性能的提高。     

元件焊端镀层对无铅焊点可靠性的影响

电子产品无铅化的转变加速了对元件焊端镀层的无铅化研究，目前候选无铅镀层有纯锡、锡铋或锡铜合金。当然,Sn—Ag—Cu焊料和以上这些镀层结合而构成的焊点的可靠性是大家关注的重点。Sn—Ag—Cu焊料和元件焊端镀层若不相容会导致焊点变脆、强度降低、缺乏热疲劳抵抗力，特别在产品生命周期的后期。对焊点的可靠性影响尤为明显。在本中我们研究了由Sn-3．8Ag-0．7Cu焊料和不同的元件焊端镀层：纯锡、Sn-3Cu、锡铋合金(铋的重量百分比分别为1％、3％、6％)组成的SMT焊点可靠性。中给出了焊点金相分析、焊点老化前和老化后的引脚拉伸测试的试验结果，首次发表了SMT焊点加速热循环试验的结果，也提到了Sn—Bi和Sn—Pb镀层对波峰焊焊点可靠性的少量研究结果。通过我们的研究发现，所有试验元件的无铅镀层和Sn—Ag—Cu焊料构成的焊点性能至少和常规的锡铅焊点一样好。     

Contact resistance and shear strength of the solder joints formed using Cu bumps capped with Sn or Ag/Sn layer

Solder joints were successfully bonded by joining Ag/Sn/Cu bumps and Ag/Sn/Cu layers at 200°C for 30 sec under 20 MPa, 40 MPa, and 80 MPa using thermo-compression bonder. The solder joints were aged at 150°C up to 1000 h. The strength of the solder joints was measured by the shear test and the contact resistance was measured using four-point probe method. The microstructure of the solder joints and the fracture modes after shear test were analyzed by scanning electron microscopy (SEM) with the energy-dispersive spectrometry (EDS). Results showed that the electrical resistance of the solder joints decreased, and the shear strength of the solder joints increased after aging treatment. The fracture modes were observed to move from the interfacial failure between solder and intermetallic compounds (IMCs) to the interfacial failure between IMCs. It was considered that the transition of fracture modes was closely related with the microstructure evolution of the solder joints, especially the transformation of IMC phases during the aging treatment.     

Pb-free Sn/3.5Ag electroplating bumping process and under bump metallization (UBM)

Pb-free solder is one of the biggest issues in today's electronic packaging industry. This paper introduces a newly developed Sn/3.5Ag alloy plating process for wafer level bumping. The effects of Under Bump Metallization (UBM) on the process, interfacial reaction, and mechanical strength have been investigated. Four different types of sputtering-based UBM layers-TiW/Cu/electroplated Cu, Cr/CrCu/Cu, NiV/Cu, and TiW/NiV-were fabricated with eutectic Pb/63Sn and Sn/3.5Ag solder. The result shows that the Sn/Ag solder gains Cu or Ni from UBM's and becomes Sn/Ag/Cu or Sn/Ag/Ni during reflow process. Sn/Ag solder has higher reactivity with Cu and Ni than Pb/63Sn. The Intermetallic Compound (IMC) spalling from the interface between UBM/solder has been observed on Cr/CrCu/Cu and TiW/NiV UBM's. However, the IMC spalling phenomena did not decrease the bump shear strength with a bump size of 110 /spl mu/m, whereas a size of 60 /spl mu/m brought a decrease in shear value and failure mode change.     

添加Sb和LaB6对Sn3.0Ag0.5Cu/Cu界面IMC生长的影响

研究了Sb和稀土化合物的添加对Sn3.0Ag0.5Cu无铅焊料焊接界面金属间化合物层生长的影响。研究结果表明,固态反应阶段界面化合物层的生长快慢排序如下:v(SAC0.4Sb0.1LaB6/Cu)v(SAC0.4Sb/Cu)v(SAC0.1LaB6/Cu)v(SAC/Cu)。计算各种界面IMC生长的激活能Q结果表明,Sn3.0Ag0.5Cu/Cu界面IMC生长的激活能最高,为92.789 kJ,其他焊料合金Sn3.0Ag0.5Cu0.4Sb0.1LaB6/Cu,Sn3.0Ag0.5Cu0.1LaB6/Cu和Sn3.0Ag0.5Cu0.4Sb/Cu界面IMC生长的激活能分别为85.14,84.91和75.57 kJ。在老化温度范围内(≤190℃),Sn3.0Ag0.5Cu0.4Sb0.1LaB6/Cu的扩散系数(D)最小,因而其界面化合物的生长速率最慢。     

Kinetics of interface reaction in 40Sn-Bi/Cu and 40Sn-Bi-2Ag/Cu systems during aging in solid state

The characteristics of thickening kinetics of the intermetallic compounds (IMC) (Cu/sub 6/Sn/sub 5/+Cu/sub 3/Sn) during aging at 120/spl deg/C and 90/spl deg/C in solid state were studied by quantitative metallographic analysis for three solder alloy systems: 40Sn-Bi/Cu, 40Sn-Bi-2Ag/Cu and Sn-37Pb/Cu. The diffusion couples were prepared by hot immersion in the molten solder bath. The results showed that the rate of the IMC thickening increases in the order Sn-37Pb/Cu<40Sn-Bi/2-Ag/Cu<40Sn-Bi/Cu. The IMC thickening rate in the Sn-Bi eutectic system is one order of magnitude faster than that in Sn-Pb eutectic system. The time exponents are different from each other. The relationship between the increase of IMC and aging time follows a parabolic function in the Sn-Pb system, and a linear relation in the Sn-Bi system. Addition of Ag in Sn-Bi inhibits the IMC thickening process.     

A reliability comparison of electroplated and stencil printed flip-chip solder bumps based on UBM related intermetallic compound growth properties

The effects of under bump metallurgy (UBM) microstructures on the intermetallic compound (IMC) growth of electroplated and stencil printed eutectic Sn-Pb solder bumps were investigated. The process parameters and their effects on UBM surface morphology and UBM shear strength were studied. For the electroplating process, the plating current density was the dominant factor to control the Cu UBM microstructure. For the stencil printing process, the zincation process has the most significant effect on the Ni UBM surface roughness and Ni grain sizes. In both processes, the good adhesion of UBM to aluminum can be obtained under suitable UBM processing conditions. Samples with different UBM microstructures were prepared using the two processes. The resulting samples were thermal aged at 85/spl deg/C, 120/spl deg/C, and 150/spl deg/C. It was observed that the Cu UBM surface roughness had larger effect on the IMC growth and solder ball shear strength than the Ni UBM surface roughness. The thickness of Cu/sub 3/Sn and Cu/sub 6/Sn/sub 5/ IMC depended strongly on the UBM microstructure. However, for Ni/Au UBM, no significant dependence was observed. More likely, the thickness of Au-Ni-Sn IMC near the IMC/solder interface was controlled by the amount of gold and the gold diffusion rate in the solder. Shear tests were performed after thermal aging tests and thermal/humidity tests. Different failure modes of different sample groups were analyzed. Electroless Ni UBM has been developed because it is a mask-less, low-cost process compared to electroplated Cu UBM. This study demonstrated that the process control was much easier for Ni UBM due to its lower reactivity with Sn material. These properties made Ni UBM a promising candidate for the lead-free solder applications.     

La对Sn3.5Ag0.5Cu钎料界面组织和性能的影响

通过SEM和EDAX等,研究了La添加量对Sn3.5Ag0.5Cu钎料与Cu基体焊合界面IMC微观组织及性能的影响。结果表明:添加不同量的La均对Sn3.5Ag0.5Cu与Cu基体焊合后的组织有细化作用并增强其力学性能。其中以w(La)达到0.05%时最优,剪切强度可提高10.7%。材料热力学理论计算结果表明,La具有"亲Sn"倾向,添加少量La到Sn3.5Ag0.5Cu钎料中,可减小Cu6Sn5/Cu界面Sn的活度,降低IMC的长大驱动力。     

Interfacial reaction and failure mode analysis of the solder joints for flip-chip LED on ENIG and Cu-OSP surface finishes

The interfacial reactions and failure modes of the solder joints for flip-chip light emitting diode (LED) on electroless nickel/immersion gold (ENIG) and Cu with organic solderability preservatives (Cu-OSP) surface finishes were investigated in this study. The experimental results demonstrate that the interfacial reactions in the Au/Sn–Ag–Cu(SAC)/ENIG and Au/SAC/Cu systems are different but the failure mechanisms of the two types of solder joints are similar during the shear test. For the Au/SAC/ENIG system, the Au layer on the surface finish of the diodes dissolved into the molten solder and transformed into a continuous (Au, Ni)Sn₄ IMC layer at the diode/solder interface during reflow and the interfacial IMC at the solder/ENIG interface is dendritic Ni₃Sn₄ IMC grains which are surrounded by (Au, Ni)Sn₄. For the Au/SAC/Cu system, however, no IMC layers can be observed at the diode/solder interface. The interfacial IMC at the solder/Cu interface is (Cu, Au)₆Sn₅ and a Cu₃Sn IMC layer at the (Cu, Au)₆Sn₅/Cu interface. Tiny (Au, Cu)Sn₄ IMC grains distribute in the solder layer and surround the (Cu, Au)₆Sn₅ grains. For the two types of systems, the primary failure mode for the cathode is due to the broken of the Si-based insulation layer which led to a high residue stress and poor connection between the Si-based layer and the solder layer. Meanwhile, the failure of the solder joint for the anode is mainly because of the failure of the solder layer under the conductive via. The crack generally forms at this area and then propagated along the diode or the diode/solder interface.     

Sn3.8Ag0.7Cu和Sn37Pb焊点界面显微结构研究

利用扫描电子显微镜（SEM）和透射电子显微镜（TEM）研究了Sn3.8Ag0.7Cu（Sn37Pb）/Cu焊点在时效过程中的界面金属间化合物（IMC）形貌和成份。结果表明：150℃高温时效50、100、200、500h后,Sn3.8Ag0.7Cu（Sn37Pb）/Cu焊点界面IMC尺寸和厚度增加明显,IMC颗粒间的沟槽越来越小。50h时效后界面出现双层IMC结构,靠近焊料的上层为Cu6Sn5,邻近基板的下层为Cu3Sn。之后利用透射电镜观察了Sn37Pb/Ni和Sn3.8Ag0.7Cu/Ni样品焊点界面,结果显示,焊点界面清晰,IMC晶粒明显。     

Microstructure characterization of SnAgCu solder bearing Ce for electronic packaging

The creep-rupture lives of Sn3.8Ag0.7Cu and Sn3.8Ag0.7Cu0.03Ce lead-free solder joints for electronic packaging were investigated, respectively. And the relationship between creep behavior and intermetallic compound (IMC: Ag₃Sn, Cu₆Sn₅, CeSn₃) particles in SnAgCu/SnAgCuCe solder joints has been obtained. Meanwhile, rare earth Ce concentration gradient and retardation effect of Ce on the IMC layer have been observed at the solder/Cu interface. Moreover, aging reaction of Sn and Cu, and the effect mechanism of rare earth Ce on two IMCs (Cu₆Sn₅ and Cu₃Sn) are reported.