Sn基液态钎焊界面气泡及IMC生长数值模拟研究

发布时间：2018-05-08 22:03

  本文选题：可靠性 + 钎料气泡　； 参考：《大连理工大学》2016年博士论文

【摘要】：随着电子封装工业不断小型化、无铅化,焊点的可靠性也引起了广大研究者的高度重视。在以铜为基体的锡基钎料焊点或对接接头结构中,除钎料／基体界面生成脆性IMC的厚度和形状是影响焊接强度的关键因素外,界面区的气泡和微孔洞等缺陷可降低焊点有效连接面积,并会产生应力集中,同样是导致焊点失效的重要隐患。因此,深入研究界面气泡生长、演化行为；界面IMC生长行为；气泡存在对界面IMC生长影响等,不仅可以深入阐明钎焊机理,同时对提高钎焊接头可靠性有重要的理论指导意义。本文应用同步辐射实时成像技术及常规钎焊试验对界面气泡进行了深入研究,并对温度梯度与电势梯度作用下钎焊过程中界面IMC的生长行为进行了研究,利用以上研究结果,结合数值模拟手段,重点创建了FEM模型、AEH方法和DANPHE软件,引用FVM模型和Elmer软件、FiPy软件对钎焊过程气泡生长、演化行为及场梯度条件下界面IMC生长行为进行了模拟分析,获得以下结果：(1)应用同步辐射实时成像技术对液态Sn/Cu界面上初始直径为20μm的气泡生长进行在线观察,以此为基础创建一种基于有限元法的数值模型(FEM)引用Elmer软件对此过程进行模拟分析。同步辐射结果显示,动态生长界面IMCs上的气泡生长会经历一个由润湿控制的转变过程：气泡与IMCs的接触角会从最初的钝角不断减小,向直角(半球气泡点)、锐角转化,直到气泡完全变为圆形达到动态平衡；数值模拟结果显示,气泡与IMCs接触角越大,气泡的最终尺寸也越大,相同的钎焊时间内平均生长速度就越大；综合同步辐射和数值模拟结果可知,气泡在早期生长较快,后期生长较慢。(2)研究气泡对界面IMCs生长影响发现,气泡的存在阻隔了钎料和铜基体的反应,将界面IMC划分为不生长、半生长和全生长三类IMCs。不生长IMC是指气泡正下方,由于受到气泡的阻碍钎料无法与基板接触,完全不能生长的IMC；半生长IMC是指临近气泡区域,受到气泡的影响部分生长的IMC；全生长IMC是指远离气泡,不受气泡影响而完全生长的IMC。因此,根据半生长和全生长IMC的界限可以预测气泡的尺寸。(3)在含有气泡的液固界面上,钎料中气泡的存在会导致周围材料物理性能的变化,进而影响钎焊过程。应用以FEM模型为基础的渐进扩展均匀化AEH方法,模拟计算出含气泡熔融焊料中垂直界面方向Cu的有效扩散系数和Sn热导率等影响钎焊物理参数的变化,以此评估气泡存在时钎焊焊点的质量。(4)在温度梯度下IMC生长研究中,创立了一种以MOOSE结构为基础的DANPHE软件,应用FEM模型对钎焊过程进行了模拟,模拟结果与常规钎焊和同步辐射实时成像技术测得是实验数据吻合,模型应用准确。结果显示：相对250℃,350℃纯Sn体系对接焊点冷端IMC厚度较大,说明相同温度梯度下,钎焊温度越高,冷端IMC生长速率越快；同时发现,350℃下Sn3.5Ag钎料中冷端IMC生长厚度小于纯Sn中IMC厚度,说明Ag3Sn的形成抑制了冷端界面IMC的生长。(5)在电势梯度试验条件下,应用已创建的FEM模型/DANPHE软件或引用FVM(有限元体积法)模型/FiPy软件进行数值模拟,同时应用已创建的FEM模型/DANPHE软件计算焦耳热。结果显示,模拟数据与同步辐射实时成像技术观察阳极IMC生长行为(试验条件为250℃间距为450μm和1.234mm的Cu/Sn/Cu对接焊点分别通以0.56×103 A/cm2和3.0×103 A/cm2的电流进行回流)的试验数据非常吻合,模型应用准确；电势梯度下,阳极IMCs厚度随钎焊时间呈线性增长,符合线性动力学关系；电流密度越大,线性斜率越大,阳极IMC生长越快；同时发现在钎焊过程中焊点的温度会有变化,低电流密度下液态钎料的温度变化较小,3.0×103A/cm2的电流密度下焊点温度则提高了近40℃,但电迁移驱动力对IMC生长的作用依然明显大于扩散梯度的影响；对接焊点间距越大,电场下后期阳极IMC增长越快。
[Abstract]:With the miniaturization and lead-free of the electronic packaging industry, the reliability of the solder joints has been paid great attention by the researchers. In the solder joints or butt joints of copper based solder joints, the thickness and shape of the brittle IMC generated by the solder / substrate interface are the key factors affecting the welding strength, and the bubbles and micropores in the interface zone Holes and other defects can reduce the effective connection area of the solder joints and produce stress concentration, which is also an important hidden danger in the failure of the solder joints. Therefore, the deep study of the growth and evolution behavior of the interface bubbles, the growth behavior of the interface IMC, the effect of the existence of bubbles on the growth of the interface IMC, and so on, can not only clarify the brazing mechanism, but also improve the brazing joint. It has important theoretical guiding significance. In this paper, the interface bubbles are studied by the real-time imaging technology of synchrotron radiation and the conventional brazing test. The growth behavior of the interface IMC in the brazing process under the effect of temperature gradient and potential gradient is studied. FEM model, AEH method and DANPHE software, FVM model and Elmer software, FiPy software are used to simulate the bubble growth, evolution behavior and interfacial IMC growth behavior under the field gradient conditions. The following results are obtained: (1) the growth of bubble growth with initial diameter of 20 mu on the liquid Sn/Cu interface is obtained by using real-time synchrotron radiation imaging technology. A numerical model based on the finite element method (FEM) is built on the basis of the finite element method (FEM) to simulate the process. The synchrotron radiation results show that the bubble growth on the dynamic growth interface will undergo a transition process by the wetting control: the contact angle between the bubble and the IMCs will continue from the original obtuse angle. The results show that the larger the contact angle between the bubbles and IMCs, the larger the bubble size, the greater the average growth rate in the same brazing time, and the results of synchrotron radiation and numerical simulation show that the bubble is in the early stage. Growth is faster and later growth is slow. (2) the study of the effect of bubble on the growth of interface IMCs found that the existence of bubbles obstructed the reaction between the brazing and the copper matrix, divided the interface IMC into non growth, and the semi growth and full growth of the non growth of the IMCs. IMC means that the bubble was under the front of the bubble, and the brazing filler metal could not be exposed to the substrate because of the obstruction of the bubble. Long IMC; half long IMC refers to the IMC that is growing near the bubble region and affected by bubbles; the full growth IMC is a IMC. that is completely grown away from the bubble and is not affected by the bubble. Therefore, the size of the bubble can be predicted according to the boundary of semi growth and full growth of IMC. (3) the existence of bubbles in the liquid and solid interface containing bubbles. The physical properties of the surrounding materials will be changed and the brazing process will be influenced. The incremental and homogenized AEH method based on the FEM model is applied to simulate the effect of the effective diffusion coefficient and the thermal conductivity of the Sn on the physical parameters of the brazing, which can be used to evaluate the brazing solder joint in the presence of the bubble in the molten solder. (4) in the study of IMC growth under the temperature gradient, a kind of DANPHE software based on the MOOSE structure was founded. The brazing process was simulated with the FEM model. The simulation results were consistent with the conventional brazing and synchrotron radiation real-time imaging technology, and the model type application was accurate. The results showed that the pure Sn body was 250 and 350. The IMC thickness at the cold end of the butt joint shows that the higher the brazing temperature, the faster the growth rate of the cold end IMC under the same temperature gradient. At the same time, it is found that the growth thickness of the cold end IMC is less than the IMC thickness in the pure Sn at 350 C, indicating that the formation of Ag3Sn inhibits the growth of IMC at the cold end interface. (5) under the condition of the potential gradient test, the application has been established. The FEM model /DANPHE software or the FVM (finite element volume) model /FiPy software is used to simulate the numerical simulation, and the Joule heat is calculated with the created FEM model /DANPHE software. The results show that the simulation data and synchrotron radiation real-time imaging technique observe the growth behavior of the anode IMC (the test condition is 250 c interval of 450 mu m and 1.234mm Cu/Sn/. " The test data of Cu butt solder joint with 0.56 x 103 A/cm2 and 3 x 103 A/cm2 current respectively coincide with the experimental data, and the application of the model is accurate. Under the potential gradient, the anode IMCs thickness is linearly increased with the brazing time, which is in line with the linear dynamics; the greater the current density, the greater the linear slope, the faster the growth of the anode IMC, and found at the same time. The temperature of solder joints will change in the process of brazing, and the temperature of the liquid solder is smaller under the low current density. The temperature of the solder joint is nearly 40 degrees under the current density of 3 x 103A/cm2, but the effect of the electromigration drive on the growth of IMC is still greater than the effect of the diffusion gradient; the larger the distance between the butt welding points and the growth of the anode IMC in the later stage of the electric field The faster.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG40
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本文编号：1863253