Electrochemical migration behaviors of lead-free 64Sn-35Bi-1Ag solder on FR-4 PCB board plated with Cu

Electrochemical migration (ECM) characteristic is a new reliability failure. A parallel surfacial electrode system coupling with scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), and X-ray Diffraction (XRD) technologies is designed to research ECM behavior of 64Sn-35Bi-1Ag (SBA) solder in 3.5 g/L NaCl solution and compare to that of Sn37Pb and Sn-3.0Ag-0.5Cu (SAC) solders. Results show that SBA solder is more susceptible to ECM failure than Sn37Pb solder, which is more difficult than SAC solder. The affected factors of ECM are given as follows: the solder compositions, the loaded electric field, ECM time, etc. The electrochemical reaction mechanism of ECM process is achieved. EDAX and XRD analyses show that the main contents on dendrites of SBA solder after ECM test are Sn, hardly any Bi, a little Ag, which illustrates that the order of ion migration capacity is shown as follows: Sn Ag Bi.     

SnBi/Cu焊接接头的剪切性能及界面微观组织分析

通过对断口形貌和界面微观组织的观察分析,研究了3种Sn-Bi/Cu焊接接头的剪切断裂机理.结果表明:3种Sn-Bi/Cu焊接接头均在弹性变形阶段断裂,并且均沿Sn-Bi焊料/Cu基板界面处断裂.孔洞降低了3种Sn-Bi/Cu焊接接头的有效连接面积,从而降低了其剪切强度.根据3种Sn-Bi/Cu焊接接头断口形貌,Sn59.9Bi40Cu 0.1/Cu和Sn57.9Bi40Zn2Cu 0.1/Cu焊接接头剪切断裂机制属于准解理、沿晶脆性断裂和韧窝的混合型断裂,而Sn42Bi58/Cu焊接接头剪切断裂机制属于准解理断裂.微观组织分析显示,3种焊料合金焊接接头界面处的金属间化合物层均为连续的Cu₆Sn₅相.     

BGA封装中含Bi,Ni的无铅焊球剪切强度研究

对Sn/3.5Ag/0.7Cu,Sn/3Ag/3Bi/0.5Cu和Sn/3Ag/3Bi/0.5Cu/0.1Ni三种BGA无铅焊球(0.76 mm)经不同热循环后,在FR-4基板上的剪切强度进行了测量.采用SEM和EDX对样品截面进行观察和元素分析.数据表明,Bi的掺入提高了焊料的润湿性及焊接强度,并减缓了IMC的生长速度;焊料中加入微量Ni可有效减小焊点下金属上Ni镀层的耗穿速度,抑制了焊球经热循环后焊接强度的下降.     

Effect of Ag and Ni on the melting point and solderability of SnSbCu solder alloys

To improve the properties of Sn10Sb8Cu solder alloy, two new solders (SnSbCuAg and SnSbCuNi) were formed by adding small amounts of Ag or Ni into the solder alloy. The results show that the melting point of the SnSbCuAg solder alloy decreases by 14.1℃ and the spreading area increases by 16.5% compared to the matrix solder. The melting point of the SnSbCuNi solder alloy decreases by 5.4℃ and the spreading area is slightly less than that of the matrix solder. Microstructure analysis shows that adding trace Ag makes the melting point decline due to the dispersed distribution of SnAg phase with low melting point. Adding trace Ni, Cu₆Sn₅ and (Cu, Ni)₆Sn₅ with polyhedron shape on the copper substrate can be easily seen in the SnSbCuNi solder alloy, which makes the viscosity of the melting solder increase and the spreading property of the solder decline.     

回流次数对Sn3.5Ag0.5Cu焊点特性的影响

研究了回流次数对Sn3．5Ag0．5Cu焊点特性的影响，采用扫描电镜SEM和光学显微镜对多次回流后Sn3．5Ag0．5Cu焊点界面金属间化合物（IMC）层的形貌和拉伸断裂断口形貌进行了分析．结果表明：随着回流次数的增加，焊点的宽度和金属间化合物的厚度增加；焊料和凸点下金属化层（UBM）之间界面上的IMC组织从针状逐渐粗化；焊料的拉伸强度有轻微变化；断裂面第一次回流焊后出现在焊料中，而多次回流焊后断裂面部分出现在焊料中，部分出现在UBM和焊料的界面中．     

Spreading kinetics of a Sn-30Bi-0.5Cu alloy on a Cu substrate

The reactive wetting kinetics of a Sn-30Bi-0.5Cu Pb-free solder alloy on a Cu substrate was investigated by the sessile drop method from 493 to 623 K.The triple line frontier,characterized by the drop base radius R was recorded dynamically with a high resolution CCD using different spreading processes in an Ar-H 2 flow.We found a good agreement with the De Gennes model for the relationship between ln(dR/dt) and lnR for the spreading processes at 493 and 523 K.However,a significant deviation from the De Gennes model was found for the spreading processes at 548 and 623 K.Our experimental results show a complicated temperature effect on the spreading kinetics.Intermetallics at the Sn-30Bi-0.5Cu/Cu interface were identified as Cu 6 Sn 5 adjacent to the solder and Cu 3 Sn adjacent to the Cu substrate.The intermetallic compounds effectively enhanced the triple line mobility because of reaction product formation at the diffusion frontier.     

Hillock Sn whiskers growth behaviors in Sn0.3Ag0.7Cu/Cu solder joints during corrosion

Hillock Sn whiskers in Sn0.3Ag0.7Cu solder are investigated in 20 seconds in corrosive climate(95% methanol and 5% nitric acid),and the growth mechanism of hillock Sn whiskers is studied.The results indicate that hillock Sn whiskers are formed near the interface of Sn0.3Ag0.7Cu/Cu solder joints,and small corrosion pits provide conceive sites for Sn whiskers. Moreover,compressive stress induced by IMC reaction and oxidation for the whisker growth may be suggested as the driving force.     

无钎焊料与Zr基块状非晶合金的润湿行为

通过座滴法研究了Sn-In、Sn-Bi和Sn-Ag-Cu三种焊料分别与块状非晶合金Zr44Cu40Al8Ag8的润湿行为.结果显示在三种焊料中,Sn-In对块状非晶合金Zr44Cu40Al8Ag8的润湿性最好,而Sn-Bi焊料对块状非晶合金Zr44Cu40Al8Ag8的润湿性最差.利用扫描电镜研究了Sn-In焊料与块状非晶合金Zr44Cu40Al8Ag8的界面特征,其界面处有化合物出现.     

Ag对Sn-57Bi无铅钎料组织和性能的影响

研究了在Sn-57Bi近共晶合金的基础上加入少量的Ag后对Sn-57Bi钎焊料铸态组织、抗拉强度和Sn-57Bi／Cu焊接性能的影响。试验结果表明，ωAg=0．1％～1．0％可使合金的共晶组织变细，β-Sn枝晶相的尺寸变小，提高其抗拉强度；使Sn-57Bi／Cu接头的剪切强度有所提高。     

快速凝固Al-Cu钎料钎焊铝Cu对钎缝组织的影响

研究了快速凝固钎料中Cu元素在铝合金基体中的扩散现象和机制.采用快速凝固的方法制备出了Al-Cu合金的薄带,用差热分析法(DTA)测量了钎料熔点.根据熔点利用真空钎焊用Al-Cu钎料焊接纯铝,然后使用扫描电镜和能谱分析仪分析了焊缝的显微组织,对Cu元素的扩散现象进行观察,并分析了Cu的扩散行为.实验结果表明,由于快冷钎料组织均匀,表面能高,因此熔点比普通钎料低,且熔化区间窄.随着钎焊温度的升高和保温时间的延长,Cu的扩散效果越来越好;在同一温度下钎焊时,快冷钎料中Cu的扩散能力明显强于普通钎料.     

Effects of nano-sized Ag reinforcing particulates on the microstructure of Sn-0.7Cu solder joints

Composite solders were prepared by mechanically dispersing different volumes of nano-sized Ag particles into the Sn-0.7Cu eutectic solder. The effects of Ag particle addition on the microstructure of Sn-0.7Cu solder joints were investigated. Besides, the effects of isothermal aging on the microstructural evolution in the interfacial intermetallic compound (IMC) layer of the Sn-0.7Cu solder and the composite solder reinforced with 1vol% Ag particles were analyzed, respectively. Experimental results indicate that the growth rate of the interfacial IMC layer in the Ag particles reinforced composite solder joint is much lower than that in the Sn-0.7Cu solder joint during isothermal aging. The Ag particles reinforced composite solder joint exhibits much lower layer-growth coefficient for the growth of the IMC layer than the corresponding solder joint.     

Interfacial intermetallic compound growth and shear strength of low-silver SnAgCuBiNi/Cu lead-free solder joints

The growth rule of the interfacial intermetallic compound (IMC) and the degradation of shear strength of Sn-0.8Ag-0.5Cu-2.0Bi-0.05Ni (SACBN)/Cu solder joints were investigated in comparison with Sn-3.0Ag-0.5Cu (SAC305)/Cu solder joints aging at 373, 403, and 438 K. The results show that (Cu_1?x,Ni_x)₆Sn₅ phase forms between the SACBN solder and Cu substrate during soldering. The interfacial IMC thickens constantly with the aging time increasing, and the higher the aging temperature, the faster the IMC layer grows. Compared with the SAC305/Cu couple, the SACBN/Cu couple exhibits a lower layer growth coefficient. The activation energies of IMC growth for SACBN/Cu and SAC305/Cu couples are 111.70 and 82.35 kJ/mol, respectively. In general, the shear strength of aged solder joints declines continuously. However, SACBN/Cu solder joints exhibit a better shear strength than SAC305/Cu solder joints.     

Low melting point nanocrystalline Sn–Ag solder synthesized by a refined chemical reduction method

The commercial market of Sn-Pb solder is gradually decreasing due to its toxicity, calling for Pb-free substitute materials. Sn-Ag alloy is a potential candidate in terms of good mechanical property. The major problematic issue of using Sn-Ag is their high melting temperature, consequently this study is dedicated to lowering the melt- ing temperature of Sn3.5Ag （wt%） alloy by developing nanomaterials using a chemical reduction approach. The resultant nanocrystalline Sn3.5Ag is characterized by field emission scanning electron microscope. The size dependence of the melting temperature is discussed based on differential scanning calorimetry results. We have reduced the melting temperature to 209.8 ℃ in the nanocrystalline Sn3.5Ag of （32.4± 8.0） nm, compared to ～221 ℃ of the bulk alloy. The results are consistent with the prediction made by a relevant theoretical model, and it is possible to further lower the melting temperature using the chemical reduction approach developed by this study.     

Influence of Temperature on Creep Behavior of Ag Particle Enhancement SnCu Based Composite Solder

The creep properties of solder alloys are an important factor affecting the reliability of soldered joints in surface mount technologies. Particle-enhancement is one way to improve the properties of solder alloys. The temperature of the solder joint is one of the primary factors affecting the solder joint creep prop-erties. Single shear lap creep specimens with a 1 mm2 cross-sectional area were fabricated using Ag parti-cle enhancement 99.3Sn0.7Cu based composite solder and 99.3Sn0.7Cu eutectic solder to examine the in-fluence of temperature on the creep behavior of solder joints. The results show that the solder joint creep resistance of the composite solder joint was generally superior to that of the 99.3Sn0.7Cu solder joint. The creep rupture life of the composite solder joint was reduced by increasing temperatures at a faster rate than that of the 99.3Sn0.7Cu eutectic solder joint.     

Electrical conductivity changes of bulk tin and Sn-3.0Ag-0.5Cu in bulk and in joints during isothermal aging

The changes of electrical conductivity (resistance) between Sn-3.0Ag-0.5Cu solder joints and printed circuit board (PCB) assembly during aging at 125℃ were investigated by the four-point probe technique. The microstructural characterizations of interfacial layers between the solder matrix and the substrate were examined by optical microscopy and scanning electronic microscopy. Different types of specimens were designed to consider several factors. The experimental results indicate that electrical conductivities (resistances) and residual shear strengths of the solder joint specimens significantly decrease after 1000 h during isothermal aging. Microcracks generate in the solder matrix at the first 250 h. Besides, the evolutions of microstructural characterizations at the interface and the matrix of solder joints were noted in this research.     

Abnormal growth of Ag_3Sn intermetallic compounds in Sn-Ag lead-free solder

Tin-lead solders have been used for some 2000 years and applied widely in the assembly of modern elec-tronic circuits. However, Pb is harmful to the nervous system of human beings and hazardous to the environ-ment. The European Union directive on waste el…     

Abnormal growth of Ag3Sn intermetalUc compounds in Sn-Ag lead-free solder

The abnormal growth of Ag3Sn intermetallic compounds in eutectic Sn-3.5% Ag solder was investigated through high-temperature aging treatment. Microstructural evolutions of this solder before and after the aging treatment were observed by optical microscopy and scanning electron microscopy. Precise differential thermal analysis was made to study the changes in enthalpies of the solder under different conditions. The results reveal that the water-cooled solder is in metastable thermodynamic state due to the high free energy of Ag3Sn nanoparticles, which sporadically distribute in the matrix as second-phase. The second-phase Ag3Sn nanoparticles aggregate rapidly and grow to form bulk intermetallic compounds due to the migration of grain boundary between primary Sn-rich phase and the Ag3Sn nanoparticles during high temperature aging treatment.     

Microstructural evolutions of Cu(Ni)/AuSn/Ni joints during reflow

Interfacial reactions of the Ni/AuSn/Ni and Cu/AuSn/Ni joints are experimentally studied at 330℃for various reflow times.The microstructures and mechanical properties of the as-solidified solder joints are examined.The as-solidified solder matrix of Ni/AuSn/Ni presents a typical eutecticξ-(Au,Ni)_5Sn+δ-(Au,Ni)Sn lamellar microstructure after reflow at 330℃for 30 s.After reflow for 60 s,a thin and flat(Ni,Au)_3Sn_2 intermetallic compound(IMC) layer is formed,and some needle-like(Ni,Au)_3Sn_2 phases grow f...     

Optimization of mechanical properties of Sn-3.8Ag-0.7Cu alloys by the additions of Bi,In and Ti

Bi, In and Ti were added to Sn-3.8Ag-0.7Cu (SAC387) solder alloy to optimize the mechanical performance. The alloying effects of Bi, In and Ti on the microstructure, thermal and mechanical properties of SAC387 based solder alloys were investigated. The results demonstrate that adding 3.5 ?wt % of Bi could refine the microstructure, optimize the thermal properties, and improve the tensile strength. Meanwhile, the ductility of the solder alloys reduced evidently. Adding 2.8 ?wt % of In into SAC387–3.5 ?wt %Bi alloy could increase both the strength and ductility, which is attributed to the beneficial effect of In addition, as adding In could improve the solubility of Bi in the β-Sn matrix. Meanwhile, the melting point was reduced, and the wettability improved with the addition of In. Introducing amounts of Ti into SAC387–3.5 ?wt % Bi-2.8 ?wt % In alloy could further increase the strength. However, the ductility was significantly reduced when 0.8 ?wt % of Ti was added due to the formation of the coarse Ti₂Sn₃ phase. The undercooling was remarkably reduced with the addition of Ti. The nanoindentation tests demonstrate that the hardness increased mainly due to the hardening effect of the Bi addition. Among all the samples prepared, alloy SAC387–3.5 ?wt % Bi exhibited the highest creep resistance at the ambient temperature. Further adding In and Ti into SAC387–3.5 ?wt % Bi alloys reduced the creep resistance of the solder alloys. The mechanism associated with the different mechanical responses is also discussed in this study.     

掺杂Sb对Sn-Ag-Cu焊料性能的影响

在Sn-3．0Ag-0．5Cu系焊料中分别掺杂不同比例的Sb（锑），制备了无铅焊料合金．用DSC差示扫描量热仪测试熔点，用扫描电子显微镜对其显微组织进行分析，并对其导电性，润湿性等进行测试．实验结果表明，一定比例掺杂的Sn-Ag-Cu-Sb焊料，比未掺杂时，熔点下降不明显，但其显微组织结构更细化，导电性、润湿性有明显提高．