Sn基钎料/Cu界面柯肯达尔空洞机理研究
摘要
随着电子产品的微型化和多功能化，电子封装的密度不断增加，封装芯片和焊点（钎焊接头）的尺寸越来越小，使得反应界面占整个接头的比例越来越大。因此，界面微观组织对接头可靠性的影响也越来越大。在固态热老化处理的过程中，接头的反应界面处常会出现密度较高的柯肯达尔空洞（Kirkendall Void），其对接头可靠性的影响不容忽视，这已引起国内外研究者的广泛关注。
本文采用场发射扫描电镜（FESEM）、透射电镜（TEM）、X射线光电子能谱（XPS）和X射线衍射仪（XRD）等分析手段表征了接头反应界面的微观组织形貌、成分和物相结构；通过引入初始反应界面参照法研究了Cu和Sn元素在金属间化合物（Intermetallic compound，简称IMC）层中的扩散性质；利用磁控溅射和电镀技术制备了多种Cu基板以对比研究Sn/Cu界面处柯肯达尔空洞的形成机制；运用第一性原理方法计算了IMC晶体中空位的扩散性质，并采用有限元方法分析了反应界面处残余应力的分布，以共同研究柯肯达尔空洞与Cu_3Sn层的关联性；还向Sn/Cu体系中添加微量合金元素以研究其对柯肯达尔空洞的抑制机理。
采用接头角部区域的初始反应界面（未反应Cu基板的上表面）作为参照面，观察分析了不同相界面的迁移规律。结果表明，随着热老化时间的延长，接头中钎料(Solder)/Cu_6Sn_5和Cu_3Sn/Cu界面分别向钎料基体和Cu基板两个方向迁移，而Cu_6Sn_5/Cu_3Sn界面的迁移方向与热老化温度相关。在150℃时，Cu_6Sn_5/Cu_3Sn界面向钎料基体方向迁移；165℃时，该界面向Cu基板方向迁移；升至180℃时，该界面的相对位置基本保持恒定（除Sn0.7Cu/Cu接头，其界面向Cu基板方向迁移）。根据每个相界面的相对位置，可以建立模型来计算研究Cu和Sn在IMC层中的扩散通量及其随热老化时间的演变趋势。计算结果表明，Cu和Sn处于不平衡扩散状态，Cu为主导扩散元素，这是柯肯达尔空洞形成的基础；Cu和Sn在两种IMC层（Cu_6Sn_5和Cu_3Sn）中的扩散通量均随热老化时间的延长而减小。在热老化处理的初始阶段，Cu的扩散通量大于Sn；随着热老化时间的延长，两者的扩散通量逐渐接近。
构建了Sn/Cu体系，通过采用不同的Cu基板来对比分析影响Sn/Cu接头中柯肯达尔空洞形成的各种因素。柯肯达尔空洞没有在使用高纯基板的界面出现，而在使用真空溅射基板和电镀基板的反应界面处形成，故柯肯达尔空洞的形成与基板存在直接联系。真空溅射基板和电镀基板的晶粒尺寸很小，晶界内存储着大量能量，其中部分能量会在界面反应过程中释放并被引入界面，从而促进柯肯达尔空洞的形成。此外，电镀基板中还含有杂质，其可以降低柯肯达尔空洞的形成能。热老化过程中，界面柯肯达尔空洞的形成过程主要包括孕育期、形核期、生长期和愈合期四个阶段；柯肯达尔空洞全部在Cu_3Sn/Cu界面和Cu_3Sn层内形成，而没有在Cu_6Sn_5层出现。在Sn/Cu扩散偶中，Sn镀层内也存在多种杂质元素，但柯肯达尔空洞倾向于在Cu_6Sn_5/Cu_3Sn和Cu_3Sn/Cu界面形成，而没有在靠近Sn镀层的Cu_6Sn_5层和Sn(电镀)/Cu_6Sn_5界面出现。因此，柯肯达尔空洞与Cu_3Sn层存在很强的关联性。
分别从微观和宏观角度研究了柯肯达尔空洞与Cu_3Sn层的关联性。采用第一性原理方法研究了Cu_3Sn和Cu_6Sn_5晶体的空位扩散性质，结果表明，两种晶体中Cu空位的形成能比较接近，它们均小于相应晶体内Sn空位的形成能；两种晶体内Sn原子的扩散能垒均高于Cu原子，Cu_6Sn_5晶体中Cu原子的扩散能垒高于Cu_3Sn晶体，这些扩散性质有利于柯肯达尔空洞在Cu_3Sn晶体内形核。在接头的反应界面处，形成IMC相会导致显著的局部体积收缩，从而引入残余应力。采用有限元方法计算了界面处相变残余应力的分布，结果表明，界面Cu_3Sn层处于较大的拉应力状态；Cu_3Sn/Cu界面处的应力梯度最大，Cu_6Sn_5/Cu_3Sn界面次之，Sn/Cu_6Sn_5界面最小；而界面柯肯达尔空洞分布在最大应力梯度所在区域。界面应力梯度加剧了界面组分元素的不平衡扩散，促进了柯肯达尔空洞的形核生长。相变残余应力通过Cu_3Sn层与柯肯达尔空洞联系起来。
向Sn/Cu(电镀)体系添加微量的Cu或Zn或Ni元素均可以抑制柯肯达尔空洞的形成，但其抑制机理各异。添加Cu不会改变界面IMC层的物相和微观组织，但其会降低界面区域Cu的浓度梯度，从而阻缓Cu的扩散，减少Cu和Sn不平衡扩散的程度。添加Zn会改变界面IMC层的物相和微观组织，Zn含量较低（0.2和0.5wt.%）时，界面处形成Cu_6(Sn,Zn)_5层；含量增至0.8wt.%时，Zn在界面处出现了明显的富集，形成了(Cu,Zn)_6Sn_5、Cu_6(Sn,Zn)_5和Cu-Zn固溶合金三个层。(Cu,Zn)_6Sn_5和Cu_6(Sn,Zn)_5层的晶粒组织对界面扩散的影响不大，但富Zn的Cu-Zn固溶合金层有效地阻缓了Cu的扩散。Zn在很大程度上参与了界面扩散，其扩散方向与Sn一致，有效抑制了Cu的扩散，缓解了Cu和Sn不平衡扩散的程度。添加Ni也会改变界面IMC层的物相和微观组织，界面处形成了(Cu,Ni)_6Sn_5层，其由多层小尺寸晶粒组成。这种组织有利于界面Cu和Sn的互扩散，加速了(Cu,Ni)_6Sn_5层的生长，还缓解了Cu和Sn的不平衡扩散。三种合金元素均可以抑制Cu_3Sn层的形成，从而减少界面处杂质和相变残余应力的引入，抑制柯肯达尔空洞的形成。
With the miniaturization and multifunction of electronic products, the size of chips andsolder joints becomes smaller and smaller, which represents an increasing proportion ofinterface area in the joints. Therefore, the microstructure at the interface plays a more andmore important role in the reliability of joints. During the solid-state aging treatment of solderjoints, a large number of Kirkendall voids often appear at the reaction interface, the effect ofwhich on the reliability of joints can not be neglected and has drawn many attentions fromscholars both at home and abroad.
In this dissertation, Field emission scanning electron microscope (FESEM), Transmissionelectron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-RayDiffractormeter (XRD) are applied to characterize the microstructure, composition and phasestructure at the reaction interface of joints. A new method using the original reaction interfaceas the reference is introduced to study the diffusion of Cu and Sn in the Intermetalliccompound (IMC) layers. Magnetron sputtering and electroplating technique are used toprepare different kinds of substrates, studying the formation mechanism of Kirkendall voids.The diffusion of vacancies in the IMC crystals and the distribution of residual stress at thereaction interface are investigated by using first-principles method and finite-element method,respectively. Then, the relationship between Kirkendall voids and Cu_3Sn is analyzed.
The rules for the migration of phase interfaces are discovered by using the originalreaction interface (the upper surface of unreacted Cu substrate) in the corner of joints as thereference. The results show that, with the extension of aging period, the solder/Cu_6Sn_5andCu_3Sn/Cu interfaces move toward the solder and Cu substrate, respectively. The migration ofCu_6Sn_5/Cu_3Sn interface is greatly affected by the aging temperature. At150℃, theCu_6Sn_5/Cu_3Sn interface moves toward the solder; At165℃, the interface shifts toward the Cu substrate; At180℃, the interface keeps still except for that in Sn0.7Cu/Cu joints whichmoves toward the Cu substrate. Based on the relative positions of each phase interfaces, amodel can be build to calculate the diffusion fluxes of Cu and Sn in IMC layers and theirevolution trend with aging time. The calculated results indicate that the interfacial diffusion ofCu and Sn is unbalanced, and Cu is the dominant diffusing species, which is the basis of theformation of Kirkendall voids; the diffusion fluxes of Cu and Sn in the IMC layer decreasewith extension of aging period. In addition, the diffusion flux of Cu in the IMC layer is largerthan that of Sn at the initial stage of aging treatment, and then the diffusion fluxes of twodiffusing species are gradually close to each other.
The Sn/Cu system is built, in which various effect factors of the formation of Kirkendallvoids are studied by using different substrate in Sn/Cu joints. Kirkendall voids appear at theinterface using electroplated and sputter deposited Cu substrate rather than the interface usinghigh-purity Cu substrate. Thus, there is a direct relationship between Kirkendall voids andsubstrate. The grain size of electroplated and sputter deposited substrates is very small, and alarge amount of energy is stored in the grain boundary. Part of the stored energy can beintroduced into the interface during the reaction, accelerating the formation of Kirkendallvoids. Besides, the electroplated substrate contains a certain amount of impurities which canreduce the nucleation energy of voids. During the aging treatment, the formation ofKirkendall voids mainly consists of four stages, inoculation, nucleation, growth and closure.Kirkendall voids are formed at the Cu_3Sn/Cu interface and in the Cu_3Sn layer, while not in theCu_6Sn_5layer. In electroplated Sn/Cu couples, many impurity elements are detected in theelectroplated Sn. However, Kirkendall voids tend to form at the Cu_6Sn_5/Cu_3Sn and Cu_3Sn/Cuinterfaces rather than in the Cu_6Sn_5layer and at the electroplated Sn/Cu_6Sn_5interface, both ofwhich are close to the electroplated Sn. Therefore, there is a great relationship betweenKirkendall voids and Cu_3Sn layer.
The relationship between Kirkendall voids and Cu_3Sn layer is studied from the macro andmicro perspective, respectively. The diffusion of vacancies in Cu_6Sn_5and Cu_3Sn crystals arestudied by using first-principles method. The calculated results indicate that the vacancyformation energy of Cu in both crystals is close to each other, but is lower than that of Sn intheir corresponding crystals. In both crystals, the vacancy diffusion barrier of Sn is higherthan that of Cu, and the vacancy diffusion barrier of Cu in Cu_6Sn_5crystal is higher than that inCu_3Sn crystal. These diffusion properties are beneficial for the nucleation of Kirkendall voids in Cu_3Sn crystal. At the reaction interface, the formation of IMC phase will cause an obviousvolume contraction, and then the residual stress will be produced. The distribution of residualstress is analyzed by using finite element method. The calculated results show that the wholeCu_3Sn layer is in the state of tensive stress. The stress gradient at the Cu_3Sn/Cu layer is thesteepest, that at the Cu_6Sn_5/Cu_3Sn interface takes the second place and that at the Sn/Cu_6Sn_5interfaces the third place. The area Kirkendall voids located is consistent with that the steepeststress gradient located. The interfacial stress gradient aggravates the unbalanced diffusion ofcomponent elements, accelerating the formation of voids. The transformation residual stress isconnected to Kirkendall voids through Cu_3Sn layer.
The formation of Kirkendall voids can be inhibited by adding minor alloying elements (Cuor Zn or Ni) into the Sn/electroplated Cu system, but the inhibition mechanism of theseelements are different. The addition of Cu will not change the phases and microstructures ofIMC layers at the interface, but will decrease the concentration gradient, hampering thediffusion of Cu and reducing the unblanced diffusion of Cu and Sn. The addition of Zn canchange the phases and microstructures of IMC layers at the interface. When the content of Znin Sn solder is low (0.2and0.5wt.%), the Cu_6(Sn,Zn)_5layer is formed; when the content ofZn increases to0.8wt.%, three layers can be found,(Cu,Zn)_6Sn_5, Cu_6(Sn,Zn)_5and Cu-Znsolid-solution alloy. The microstructure of (Cu,Zn)_6Sn_5and Cu_6(Sn,Zn)_5layers has minoreffect on the interfacial diffusion, but the Cu-Zn solid-solution alloy can hamper the diffusionof Cu effectively. Zn participates in the interfacial diffusion largely, which has the samediffusion direction as Sn. Zn can suppress the diffusion of Cu effectively and reduce theunbalanced diffusion of Cu and Sn. The addition of Ni can also change the phases andmicrostructures of IMC layers at the interface. The (Cu,Ni)6Sn5layer is formed, whichcomposes of several layers of small-sized grains. This kind of structure is helpful for thediffusion of Cu and Sn, the growth of layer and the reduction of the unbalanced diffusion ofCu and Sn. All three kinds of alloy elements can suppress the growth of Cu_3Sn layer, reducingthe introduction of impurities and transformation residual stress to the interface and inhibitingthe formation of Kirkendall voids.
本文采用场发射扫描电镜（FESEM）、透射电镜（TEM）、X射线光电子能谱（XPS）和X射线衍射仪（XRD）等分析手段表征了接头反应界面的微观组织形貌、成分和物相结构；通过引入初始反应界面参照法研究了Cu和Sn元素在金属间化合物（Intermetallic compound，简称IMC）层中的扩散性质；利用磁控溅射和电镀技术制备了多种Cu基板以对比研究Sn/Cu界面处柯肯达尔空洞的形成机制；运用第一性原理方法计算了IMC晶体中空位的扩散性质，并采用有限元方法分析了反应界面处残余应力的分布，以共同研究柯肯达尔空洞与Cu_3Sn层的关联性；还向Sn/Cu体系中添加微量合金元素以研究其对柯肯达尔空洞的抑制机理。
采用接头角部区域的初始反应界面（未反应Cu基板的上表面）作为参照面，观察分析了不同相界面的迁移规律。结果表明，随着热老化时间的延长，接头中钎料(Solder)/Cu_6Sn_5和Cu_3Sn/Cu界面分别向钎料基体和Cu基板两个方向迁移，而Cu_6Sn_5/Cu_3Sn界面的迁移方向与热老化温度相关。在150℃时，Cu_6Sn_5/Cu_3Sn界面向钎料基体方向迁移；165℃时，该界面向Cu基板方向迁移；升至180℃时，该界面的相对位置基本保持恒定（除Sn0.7Cu/Cu接头，其界面向Cu基板方向迁移）。根据每个相界面的相对位置，可以建立模型来计算研究Cu和Sn在IMC层中的扩散通量及其随热老化时间的演变趋势。计算结果表明，Cu和Sn处于不平衡扩散状态，Cu为主导扩散元素，这是柯肯达尔空洞形成的基础；Cu和Sn在两种IMC层（Cu_6Sn_5和Cu_3Sn）中的扩散通量均随热老化时间的延长而减小。在热老化处理的初始阶段，Cu的扩散通量大于Sn；随着热老化时间的延长，两者的扩散通量逐渐接近。
构建了Sn/Cu体系，通过采用不同的Cu基板来对比分析影响Sn/Cu接头中柯肯达尔空洞形成的各种因素。柯肯达尔空洞没有在使用高纯基板的界面出现，而在使用真空溅射基板和电镀基板的反应界面处形成，故柯肯达尔空洞的形成与基板存在直接联系。真空溅射基板和电镀基板的晶粒尺寸很小，晶界内存储着大量能量，其中部分能量会在界面反应过程中释放并被引入界面，从而促进柯肯达尔空洞的形成。此外，电镀基板中还含有杂质，其可以降低柯肯达尔空洞的形成能。热老化过程中，界面柯肯达尔空洞的形成过程主要包括孕育期、形核期、生长期和愈合期四个阶段；柯肯达尔空洞全部在Cu_3Sn/Cu界面和Cu_3Sn层内形成，而没有在Cu_6Sn_5层出现。在Sn/Cu扩散偶中，Sn镀层内也存在多种杂质元素，但柯肯达尔空洞倾向于在Cu_6Sn_5/Cu_3Sn和Cu_3Sn/Cu界面形成，而没有在靠近Sn镀层的Cu_6Sn_5层和Sn(电镀)/Cu_6Sn_5界面出现。因此，柯肯达尔空洞与Cu_3Sn层存在很强的关联性。
分别从微观和宏观角度研究了柯肯达尔空洞与Cu_3Sn层的关联性。采用第一性原理方法研究了Cu_3Sn和Cu_6Sn_5晶体的空位扩散性质，结果表明，两种晶体中Cu空位的形成能比较接近，它们均小于相应晶体内Sn空位的形成能；两种晶体内Sn原子的扩散能垒均高于Cu原子，Cu_6Sn_5晶体中Cu原子的扩散能垒高于Cu_3Sn晶体，这些扩散性质有利于柯肯达尔空洞在Cu_3Sn晶体内形核。在接头的反应界面处，形成IMC相会导致显著的局部体积收缩，从而引入残余应力。采用有限元方法计算了界面处相变残余应力的分布，结果表明，界面Cu_3Sn层处于较大的拉应力状态；Cu_3Sn/Cu界面处的应力梯度最大，Cu_6Sn_5/Cu_3Sn界面次之，Sn/Cu_6Sn_5界面最小；而界面柯肯达尔空洞分布在最大应力梯度所在区域。界面应力梯度加剧了界面组分元素的不平衡扩散，促进了柯肯达尔空洞的形核生长。相变残余应力通过Cu_3Sn层与柯肯达尔空洞联系起来。
向Sn/Cu(电镀)体系添加微量的Cu或Zn或Ni元素均可以抑制柯肯达尔空洞的形成，但其抑制机理各异。添加Cu不会改变界面IMC层的物相和微观组织，但其会降低界面区域Cu的浓度梯度，从而阻缓Cu的扩散，减少Cu和Sn不平衡扩散的程度。添加Zn会改变界面IMC层的物相和微观组织，Zn含量较低（0.2和0.5wt.%）时，界面处形成Cu_6(Sn,Zn)_5层；含量增至0.8wt.%时，Zn在界面处出现了明显的富集，形成了(Cu,Zn)_6Sn_5、Cu_6(Sn,Zn)_5和Cu-Zn固溶合金三个层。(Cu,Zn)_6Sn_5和Cu_6(Sn,Zn)_5层的晶粒组织对界面扩散的影响不大，但富Zn的Cu-Zn固溶合金层有效地阻缓了Cu的扩散。Zn在很大程度上参与了界面扩散，其扩散方向与Sn一致，有效抑制了Cu的扩散，缓解了Cu和Sn不平衡扩散的程度。添加Ni也会改变界面IMC层的物相和微观组织，界面处形成了(Cu,Ni)_6Sn_5层，其由多层小尺寸晶粒组成。这种组织有利于界面Cu和Sn的互扩散，加速了(Cu,Ni)_6Sn_5层的生长，还缓解了Cu和Sn的不平衡扩散。三种合金元素均可以抑制Cu_3Sn层的形成，从而减少界面处杂质和相变残余应力的引入，抑制柯肯达尔空洞的形成。
With the miniaturization and multifunction of electronic products, the size of chips andsolder joints becomes smaller and smaller, which represents an increasing proportion ofinterface area in the joints. Therefore, the microstructure at the interface plays a more andmore important role in the reliability of joints. During the solid-state aging treatment of solderjoints, a large number of Kirkendall voids often appear at the reaction interface, the effect ofwhich on the reliability of joints can not be neglected and has drawn many attentions fromscholars both at home and abroad.
In this dissertation, Field emission scanning electron microscope (FESEM), Transmissionelectron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-RayDiffractormeter (XRD) are applied to characterize the microstructure, composition and phasestructure at the reaction interface of joints. A new method using the original reaction interfaceas the reference is introduced to study the diffusion of Cu and Sn in the Intermetalliccompound (IMC) layers. Magnetron sputtering and electroplating technique are used toprepare different kinds of substrates, studying the formation mechanism of Kirkendall voids.The diffusion of vacancies in the IMC crystals and the distribution of residual stress at thereaction interface are investigated by using first-principles method and finite-element method,respectively. Then, the relationship between Kirkendall voids and Cu_3Sn is analyzed.
The rules for the migration of phase interfaces are discovered by using the originalreaction interface (the upper surface of unreacted Cu substrate) in the corner of joints as thereference. The results show that, with the extension of aging period, the solder/Cu_6Sn_5andCu_3Sn/Cu interfaces move toward the solder and Cu substrate, respectively. The migration ofCu_6Sn_5/Cu_3Sn interface is greatly affected by the aging temperature. At150℃, theCu_6Sn_5/Cu_3Sn interface moves toward the solder; At165℃, the interface shifts toward the Cu substrate; At180℃, the interface keeps still except for that in Sn0.7Cu/Cu joints whichmoves toward the Cu substrate. Based on the relative positions of each phase interfaces, amodel can be build to calculate the diffusion fluxes of Cu and Sn in IMC layers and theirevolution trend with aging time. The calculated results indicate that the interfacial diffusion ofCu and Sn is unbalanced, and Cu is the dominant diffusing species, which is the basis of theformation of Kirkendall voids; the diffusion fluxes of Cu and Sn in the IMC layer decreasewith extension of aging period. In addition, the diffusion flux of Cu in the IMC layer is largerthan that of Sn at the initial stage of aging treatment, and then the diffusion fluxes of twodiffusing species are gradually close to each other.
The Sn/Cu system is built, in which various effect factors of the formation of Kirkendallvoids are studied by using different substrate in Sn/Cu joints. Kirkendall voids appear at theinterface using electroplated and sputter deposited Cu substrate rather than the interface usinghigh-purity Cu substrate. Thus, there is a direct relationship between Kirkendall voids andsubstrate. The grain size of electroplated and sputter deposited substrates is very small, and alarge amount of energy is stored in the grain boundary. Part of the stored energy can beintroduced into the interface during the reaction, accelerating the formation of Kirkendallvoids. Besides, the electroplated substrate contains a certain amount of impurities which canreduce the nucleation energy of voids. During the aging treatment, the formation ofKirkendall voids mainly consists of four stages, inoculation, nucleation, growth and closure.Kirkendall voids are formed at the Cu_3Sn/Cu interface and in the Cu_3Sn layer, while not in theCu_6Sn_5layer. In electroplated Sn/Cu couples, many impurity elements are detected in theelectroplated Sn. However, Kirkendall voids tend to form at the Cu_6Sn_5/Cu_3Sn and Cu_3Sn/Cuinterfaces rather than in the Cu_6Sn_5layer and at the electroplated Sn/Cu_6Sn_5interface, both ofwhich are close to the electroplated Sn. Therefore, there is a great relationship betweenKirkendall voids and Cu_3Sn layer.
The relationship between Kirkendall voids and Cu_3Sn layer is studied from the macro andmicro perspective, respectively. The diffusion of vacancies in Cu_6Sn_5and Cu_3Sn crystals arestudied by using first-principles method. The calculated results indicate that the vacancyformation energy of Cu in both crystals is close to each other, but is lower than that of Sn intheir corresponding crystals. In both crystals, the vacancy diffusion barrier of Sn is higherthan that of Cu, and the vacancy diffusion barrier of Cu in Cu_6Sn_5crystal is higher than that inCu_3Sn crystal. These diffusion properties are beneficial for the nucleation of Kirkendall voids in Cu_3Sn crystal. At the reaction interface, the formation of IMC phase will cause an obviousvolume contraction, and then the residual stress will be produced. The distribution of residualstress is analyzed by using finite element method. The calculated results show that the wholeCu_3Sn layer is in the state of tensive stress. The stress gradient at the Cu_3Sn/Cu layer is thesteepest, that at the Cu_6Sn_5/Cu_3Sn interface takes the second place and that at the Sn/Cu_6Sn_5interfaces the third place. The area Kirkendall voids located is consistent with that the steepeststress gradient located. The interfacial stress gradient aggravates the unbalanced diffusion ofcomponent elements, accelerating the formation of voids. The transformation residual stress isconnected to Kirkendall voids through Cu_3Sn layer.
The formation of Kirkendall voids can be inhibited by adding minor alloying elements (Cuor Zn or Ni) into the Sn/electroplated Cu system, but the inhibition mechanism of theseelements are different. The addition of Cu will not change the phases and microstructures ofIMC layers at the interface, but will decrease the concentration gradient, hampering thediffusion of Cu and reducing the unblanced diffusion of Cu and Sn. The addition of Zn canchange the phases and microstructures of IMC layers at the interface. When the content of Znin Sn solder is low (0.2and0.5wt.%), the Cu_6(Sn,Zn)_5layer is formed; when the content ofZn increases to0.8wt.%, three layers can be found,(Cu,Zn)_6Sn_5, Cu_6(Sn,Zn)_5and Cu-Znsolid-solution alloy. The microstructure of (Cu,Zn)_6Sn_5and Cu_6(Sn,Zn)_5layers has minoreffect on the interfacial diffusion, but the Cu-Zn solid-solution alloy can hamper the diffusionof Cu effectively. Zn participates in the interfacial diffusion largely, which has the samediffusion direction as Sn. Zn can suppress the diffusion of Cu effectively and reduce theunbalanced diffusion of Cu and Sn. The addition of Ni can also change the phases andmicrostructures of IMC layers at the interface. The (Cu,Ni)6Sn5layer is formed, whichcomposes of several layers of small-sized grains. This kind of structure is helpful for thediffusion of Cu and Sn, the growth of layer and the reduction of the unbalanced diffusion ofCu and Sn. All three kinds of alloy elements can suppress the growth of Cu_3Sn layer, reducingthe introduction of impurities and transformation residual stress to the interface and inhibitingthe formation of Kirkendall voids.
引文
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