微量锌对Sn-3.5Ag无铅钎料/铜界面金属间化合物生长的抑制

在钎焊和时效条件下,研究了Sn-3.5Ag无铅钎料中添加0.2%的Zn元素后对钎料/铜界面组织形貌的影响.结果表明,钎焊条件下,将0.2%的Zn元素加入到Sn-3.5Ag钎料中对Cu-Sn间的金属间化合物及其扇贝形形状不产生影响.时效处理后,0.2%Zn元素的加入对界面IMC层的厚度、组成及形态都有影响.在Sn-3.5...     

Effects of bismuth on growth of intermetallic compounds in Sn-Ag-Cu Pb-free solder joints

The effects of Bi addition on the growth of intermetallic compound （IMC） formation in Sn-3.8Ag-0.7Cu solder joints were investigated. The test samples were prepared by conventional surface mounting technology. To investigate the element diffusion and the growth kinetics of intermetallics formation in solder joint, isothermal aging test was performed at temperatures of 100, 150, and 190 ℃, respectively. The optical microscope （OM） and scanning electron microscope （SEM） were used to observe microstructure evolution of solder joint and to estimate the thickness and the grain size of the intermetallic layers. The IMC phases were identified by energy dispersive X-ray （EDX） and X-ray diffractometer （XRD）. The results clearly show that adding about 1.0% Bi in Sn-Ag-Cu solder alloy system can refine the grain size of the IMC and inhibit the excessive IMC growth in solder joints, and therefore improve the reliability of the Pb-free solder joints. Through observation of the microstructural evolution of the solder joints, the mechanism of inhibition of IMC growth due to Bi addition was proposed.     

Effects of rapid solidification on the microstructure and microhardness of a lead-free Sn-3.5Ag solder

A lead-free Sn-3.5Ag solder was prepared by rapid solidification technology. The high solidification rate, obtained by rapid cooling, promotes nucleation, and suppresses the growth of Ag3Sn intermetallic compounds （IMCs） in Ag-rich zone, yielding fine Ag3Sn nanoparticulates with spherical morphology in the matrix of the solder. The large amount of tough homogeneously-dispersed IMCs helps to improve the surface area per unit volume and obstructs the dislocation lines passing through the solder, which fits with the dispersion-strengthening theory. Hence, the rapidly-solidified Sn-3.5Ag solder exhibits a higher rnicrohardness when compared with a slowly-solidified Sn-3.5Ag solder.     

The effect of the addition of in on the reaction and mechanical properties of Sn−1.0Ag−0.5Cu solder alloy

The effects of the reduction of the Ag content and the addition of In on the mechanical properties, soldering characteristics and reaction behavior at solder/package interfaces are investigated in this study. It was found that the addition of In significantly improved the wettability of the solder at reflow temperatures ranging from 230°C to 240°C. Moreover, the addition also improves the elongation of the solder alloy, thereby increasing the toughness of the alloy. With the optimization of the In and Ag contents, a Sn−Ag−Cu−In quaternary alloy would be a strong candidate to replace the Sn-3.0Ag-0.5Cu composition.     

1.0%Zn,Ni对Sn-3.5Ag/Cu界面反应及化合物生长的影响

在微电子互连结构中,反应界面化合物层的形貌及厚度是决定焊点可靠性的一个重要因素.通过向Sn-3.5Ag共晶钎料中添加第三元素,分别研究元素Zn和Nj对Sn-3.5Ag/Cu界面反应的影响.结果表明,对于Sn-3.5Ag/Cu界面,液态反应初始生成物为Cu6Sn5,在随后的热老化阶段形成Cu3Sn化合物层;Zn元素不影响界面的初始生成相及其厚度,但在150℃老化阶段,Cu3Sn化合物的形成受到抑制,取代的是非连续的Cu5Zn化合物层,并且,化合物层增厚速度减慢;然而,当添加1.0%(质量分数)的Ni元素后,界面初始生成相为(Cu,Ni)6Sn5,该化合物层厚度明显大于前者,老化阶段界面无其它相生成.     

Effects of cooling rates on microstructure and microhardness of lead-flee Sn-3.5%Ag solders

The microstructure and microhardness of Sn-3.5%Ag solders were explored in the cooling rate ranging from 0.08 to 10^4 K/s. Under rapid cooling condition, the strong kinetic undercooling effect leads to the actual solidification process starting at the temperature lower than the equilibrium eutectic point, and the actual metastable eutectic point shifts to the higher Ag concentration. Hence, the higher the applied cooling rate is, the more the volume fraction of primary β-Sn crystal forms. At the same time, the separation of primary β-Sn crystal favors restraining the formation of bulk Ag3Sn intermetallic compounds （IMCs） in solder due to the mismatch crystalline orientation relationship, those Ag3Sn phase separating through the eutectic reaction could hardly cling to the primary β-Sn crystal and grow up. Additionally, the Vickers hardness test shows that free β-Sn and spherical Ag3Sn phase in the rapidly solidified alloy strongly improves the microhardness of the Sn-3.5%Ag solder.     

Reaction properties and interfacial intermetallics for Sn−xAg−0.5Cu solders as a function of Ag content

Wetting and interfacial reactions were investigated for Sn−xAg−0.5Cu alloys, in which the Ag content had a variation from x=1.0 to x=4.0. Differential scanning calorimetry (DSC) was used to investigate the range of the melting temperature and the solidification temperature by measuring the endothermic and the exothermic heat flow, respectively. Low Ag contents increased the melting temperature ranges and deteriorated the wetting properties such as zero cross time and wetting force measured at two seconds. The extent of undercooling increased and the thickness of intermetallic compounds (IMC) decreased as the Ag content decreased. As the Ag content decreased, the initial IMC thickness decreased due to the large undercooling and, during the solid aging at 170°C, the IMC growth slightly decelerated because of the small diffusion coefficient. For the application of good drop shock reliability, Sn−Ag−Cu solder of low Ag content should be beneficial due to the restraint of the IMC growth (Cu₆Sn₅ and Cu₃Sn) and of the coarse plate-like IMC (Ag₃Sn).     

Pb-Free solders: Part II. Application of ADAMIS database in modeling of Sn−Ag−Cu alloys with Bi additions

The ADAMIS database was used for calculation of the surface tension of the quaternary Sn−Ag−Cu−Bi liquid alloys by Butler's model. The resultant data were compared with those from the maximum bubble pressure measurements from Part I. The same thermodynamic database was next applied for the calculation of various phase equilibria. It was established that the Bi addition to the ternary Sn−Ag−Cu alloys (Sn-2.6Ag-0.46Cu and Sn-3.13Ag-0.74Cu in at.%; Sn-2.56Ag-0.26 Cu and Sn-2.86Ag-O.40Cu in mass%) causes lowering of the melting temperature and the surface tension to make the tested alloys closer to, traditional Sn−Pb solders. The simulation of the solidification by Scheil's model showed that the alloys with the higher Bi concentration are characterized by the lifting-off failure due to the segregation of Bi at the solder/substrate boundary. Thus, in modeling of new Pb-free solders, a compromise among various properties should be taken into consideration.     

细间距倒装芯片互连过程中焊点界面金属间化合物的形成与演化

利用凸点间距为100μm,高度约为45μm,焊料成分为Sn-3.0Ag-0.5Cu(质量分数,%)(SAC305)的倒装芯片与树脂基板互连封装,研究芯片单侧凸点及芯片与BT基板焊点互连回流过程中界面金属间化合物(intermetalic compound,IMC)的形成和演化.结果表明,封装互连前,在芯片单侧镍焊盘界面上形成了长针状(Ni,Cu)₃Sn₄和薄层状Ni₃P,由于反应过程中焊料基体中Cu原子的大量消耗,没有形成典型的(Cu,Ni)₆Sn₅.封装互连过程中,由于大量Cu原子从铜界面扩散到镍界面,促使镍焊盘界面(Ni,Cu)₃Sn₄逐渐转化成(Cu,Ni)₆Sn₅,形貌由针状转变成短棒状,反应后(Cu,Ni)₆Sn₅成为主要IMC层;在铜焊盘界面上,形成了一层短棒状的(Cu,Ni)₆Sn₅,由于从镍焊盘界面扩散过来的Ni原子对Cu₃Sn生长的限制作用,反应后没有形成典型的Cu₃Sn.     

Solderability and intermetallic compounds formation of Sn-9Zn-xAg lead-free solders wetted on Cu substrate

The eutectic Sn-9Zn alloy was doped with Ag (0 wt.%-1 wt.%) to form Sn-9Zn-xAg lead-free solder alloys. The effect of the addition of Ag on the microstructure and solderability of this alloy was investigated and intermetallic compounds (IMCs) formed at the solder/Cu interface were also examined in this study. The results show that, due to the addition of Ag, the microstructure of the solder changes. When the quantity of Ag is lower than 0.3 wt.%, the needle-like Zn-rich phase decreases gradually. However, when the quantity of Ag is 0.5 wt.%-1 wt.%, Ag-Zn intermetallic compounds appear in the solder. In particular, adding 0.3 wt.% Ag improves the wetting behavior due to the better oxidation resistance of the Sn-9Zn solder. The addition of an excessive amount of Ag will deteriorate the wetting property because the glutinosity and fluidity of Sn-9Zn-(0.5, 1)Ag solder decrease. The results also indicate that the addition of Ag to the Sn-Zn solder leads to the precipitation of ε-AgZn₃ from the liquid solder on preformed interfacial intermetallics (Cu₅Zn₈). The peripheral AgZn₃, nodular on the Cu₅Zn₈ IMCs layer, is likely to be generated by a peritectic reaction L + γ-Ag₅Zn₈ → ɛ-AgZn₃ and the following crystallization of AgZn₃.     

Reaction diffusions of Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> and Cu<Subscript>3</Subscript>Sn intermetallic compound in the couple of Sn-3.5Ag eutectic solder and copper substrate

The growth kinetics of intermetallic compound layers formed between Sn-3.5Ag solder and Cu substrate were investigated as a consequence of solid-state isothermal aging. Isothermal aging was carried out in a temperature range between 70°C and 200°C for 0 to 60 days. A quantitative analysis of the intermetallic compound layer thickness as a function of time and temperature was performed. The diffusion couples showed a composite intermetallic layer comprised of Cu₆Sn₅ and Cu₃Sn. The growth of intermetallic compounds followed diffusion-controlled kinetics and the layer thickness reached only 9 μm after 60 day of aging at 150°C. The apparent activation energies were calculated for the growth of the total intermetallic compound (Cu₆Sn₅+Cu₃Sn); Cu₆Sn₅ and Cu₃Sn intermetallic are 65.4, 55.4 and 75.7 kJ/mol, respectively.     

Effects of Ga,Al, Ag,and Ce multi-additions on the wetting characteristics of Sn-9Zn lead-free solder

An orthogonal method was used to evaluate the effects of Ga, Al, Ag, and Ce multi-additions on the wetting characteristics of Sn-9Zn lead-free solders by wetting balance method. The results show that the optimal loading of Ga, Al, Ag, and Ce was 0.2 wt.%, 0.002 wt.%, 0.25 wt.%, and 0.15 wt.%, respectively. Intermetallic compounds (IMCs) formed at the interface between Sn-9Zn-0.2Ga-0.002Al-0.25Ag-0.15Ce solder and Cu substrate were investigated by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis. The SEM images illustrate that the IMCs can be divided into two portions from the substrate side to the solder side: a planar Cu₅Zn₈ layer and an additional continuous scallop-like AgZn₃ layer. The EDS analysis also shows that Ga segregates in the solder abutting upon the interface. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) of the surface components of Sn-9Zn-0.2Ga-0.002Al-0.25Ag-0.15Ce solder indicate that Al aggregates at the surface in the form of Al₂O₃ protective film, which prevents the further oxidation of the solder surface. On the other hand, Ce aggregates at the subsurface, which may reduce the surface tension of the solder and improve the wettability in consequence.     

Effect of Ag addition on the corrosion properties of Sn‐based solder alloys

Corrosion properties of three different Sn‐Ag lead free solder alloys have been investigated in 0.3 wt% Na₂SO₄ solution as corrosive environment. As cast solder alloy was analyzed by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Volume fractions of the Ag₃Sn in the solders were determined by image analysis technique. Pitting potential and corrosion potential for the alloys were determined by potentiodynamic tests. Electrochemical impedance spectroscopy (EIS) was carried out to measure the film and charge transfer resistance. Alloys with lower Ag content have been found as better corrosion resistance material.     

纳米锑掺杂对回流焊Sn-3.0Ag-0.5Cu-xSb焊点界面IMC生长的影响机理

研究了纳米锑掺杂对回流焊过程中Sn-3.0Ag-0.5Cu-xSb(x=0,0.2%,1.0%和2.0%)焊点界面金属间化合物(IMC)生长动力学的影响.借助扫描电镜(SEM)观察了焊点的微观结构,利用X射线能谱分析(EDX)及X射线衍射谱仪(XRD)确定了IMC的相和成分.结果表明,部分纳米锑颗粒溶解在富锡相中形成SnSb二元相,部分纳米锑颗粒溶解在Ag₃Sn相中形成Ag₃Sb相,剩余部分沉降在界面Cu₆Sn₅金属间化合物层表面.随着纳米锑含量的增加,IMC厚度减小.当纳米锑的含量为1.0%时,IMC厚度最小.通过曲线拟合,确定出界面IMC层生长指数和扩散系数.结果表明,IMC层生长指数和扩散系数均随着纳米锑含量的增加而减小.当纳米锑的含量为1.0%,IMC层生长指数和扩散系数均有最小值,分别为0.326和10.31×10^-10 cm²/s.由热力学相图和吸附理论可知,Sn,Sb元素之间易形成SnSb化合物,引起Sn元素的活性、Cu-Sn金属间化合物形成的驱动力和界面自由能下降,从而导致Cu₆Sn₅金属间化合物生长速率下降,抑制IMC生长.     

热循环对Sn58Bi(纳米Ti)/Cu焊点界面与性能影响

为了改善Sn-58Bi低温钎料的性能,通过在Sn-58Bi低温钎料中添加质量分数为0.1%的纳米Ti颗粒制备了Sn-58Bi-0.1Ti纳米增强复合钎料。在本文中,研究了纳米Ti颗粒的添加对-55～125 _^oC热循环过程中Sn-58Bi/Cu焊点的界面金属间化合物(IMC)生长行为的影响。研究结果表明：回流焊后,在Sn-58Bi/Cu焊点和Sn-58Bi-0.1Ti/Cu焊点的界面处都形成一层扇贝状的Cu₆Sn₅ IMC层。在热循环300次后,在Cu₆Sn₅/Cu界面处形成了一层Cu₃Sn IMC。Sn-58Bi/Cu焊点和Sn-58Bi-0.1Ti/Cu焊点的IMC层厚度均和热循环时间的平方根呈线性关系。但是,Sn-58Bi-0.1Ti/Cu焊点的IMC层厚度明显低于Sn-58B/Cu焊点,这表明纳米Ti颗粒的添加能有效抑制热循环过程中界面IMC的过度生长。另外计算了这两种焊点的IMC层扩散系数,结果发现Sn-58Bi-0.1Ti/Cu焊点的IMC层扩散系数(整体IMC、Cu₆Sn₅和Cu₃Sn IMC)明显比Sn-58Bi/Cu焊点小,这在一定程度上解释了Ti纳米颗粒对界面IMC层的抑制作用。     

电流密度对Cu/Sn-9Zn/Ni焊点液-固电迁移行为的影响

采用同步辐射实时成像技术对比研究了不同电流密度对Cu/Sn-9Zn/Ni焊点液-固电迁移行为和界面反应的影响。结果表明,当电流密度为5.0×10~3A/cm~2时,无论电子方向如何,钎料中的Zn原子均定向扩散至Cu侧界面参与界面反应,导致Cu侧界面处金属间化合物(intermetallic compounds,IMC)的厚度大于Ni侧界面处IMC的厚度;而当电流密度升高至1.0×10~4和2.0×10~4 A/cm~2时,钎料中的Zn原子均定向扩散至阴极界面,界面IMC的生长表现为"反极性效应",电流密度越高界面IMC的"反极性效应"越显著。液-固电迁移过程中Cu基体消耗明显,特别是在高电流密度条件下,电子从Ni侧流向Cu侧时,Cu基体的溶解厚度与时间呈现线性关系,电流密度越高Cu基体的溶解速率越快。此外,基于焊点中原子电迁移通量J_(em)和化学势通量J_(chem)对Zn原子和Cu在不同电流密度下的迁移行为进行了研究。     

铜含量对Sn-Cu钎料与Cu、Ni基板钎焊界面IMC的影响

研究了不同铜含量的Sn-xCu钎料(x=0,0.1%,0.3%,0.7%,0.9%,1.5%)与Cu板和Ni板在260、280和290℃钎焊后界面金属间化合物(IMC)的成分和形貌。研究结果表明:钎料与Cu板钎焊时,钎焊温度越高,界面处形成的Cu6Sn5IMC厚度越大,而在同一钎焊温度下,随着钎料中铜含量的增加,IMC的厚度先减少后增加;与Ni板钎焊时,界面IMC的厚度随着铜含量的增加而增加,同时界面化合物的成分和形貌均发生了显著变化;当Cu含量小于0.3%(质量分数)时,界面处形成了连续的(CuxNi1-x)3Sn4层;而当Cu含量为0.7%时,界面处同时存在着短棒状(CuxNi1-x)3Sn4和大块状(CuxNi1-x)6Sn5IMC;当铜含量继续增大时(0.9%~1.5%),(CuxNi1-x)3Sn4IMC消失,只发现了棒状(CuxNi1-x)6Sn5IMC。讨论了钎料中Cu含量对与Cu、Ni基板钎焊接头界面化合物生长的影响,并进一步讨论了(CuxNi1-x)6Sn5IMC的形成和长大机理。     

界面Ni3Sn4微观形貌演变对微焊点力学性能的影响

针对Ni/(20 μm)Sn/Ni微焊点,研究界面金属间化合物(IMC)Ni3Sn4微观形貌演变及其对微焊点力学性能的影响,并对拉伸断口进行分析。结果表明,随着回流时间增加,Ni3Sn4 IMC厚度快速增加,其形貌也发生显著变化,由短棒状转变成长棒状,最后演变成块状;微焊点的抗拉强度表现为先减小、再持续增大的反常变化趋势,界面Ni3Sn4微观形貌演变成为主导因素,转变成长棒状的Ni3Sn4引起应力集中,造成微焊点的强度降低,继续转变成的块状Ni3Sn4增加了裂纹抗力,提高了抗拉强度。微焊点的断口形貌进一步证实了Ni3Sn4微观形貌演变对微焊点力学性能影响。创新点： 以互连高度为20 μm的Ni/Sn/Ni微焊点为研究对象,通过控制延长回流时间形成以Ni3Sn4 IMC为唯一变量实现其生长的方法,研究了Ni3Sn4 IMC的微观形貌演变对微焊点抗拉强度的影响。