【作者】 赵宁；

【导师】 王来； 潘学民；

【作者基本信息】 大连理工大学 ， 材料学， 2009， 博士

【摘要】 目前,关于无铅钎料合金的研究在世界范围内得到了广泛的关注,并取得了一定的进展和成果,其中Sn-Cu、Sn-Ag和Sn-Ag-Cu等合金系成为科学研究和商业开发的重点。在无铅钎料的实际应用中,钎焊界面反应是影响钎焊质量和接头可靠性的关键问题之一,而在钎焊时,钎料合金必然要经历从固态到液态再到固态的过程,在钎焊反应阶段钎料合金始终处于液相状态,因此,了解和掌握钎料合金的液态结构,并探讨钎料的液态结构与钎焊界面反应之间的相关性,将对理解焊点界面金属间化合物（intermetalliccompound,IMC）的生长机制和控制IMC层的生长速度起到重要的作用。本文选取Sn-xCu（x=0.7,1.5,2）和Sn-3.5Ag-xCu（x=0,0.7,1.5）两种钎料合金为研究对象,首先利用高温液态X射线衍射仪测量了它们的衍射数据,进而计算和分析了它们的液态结构。结果表明,在液态Sn-0.7Cu和Sn-1.5Cu钎料中只测取到短程有序结构,而在260℃和330℃下Sn-2Cu熔体中不仅存在短程有序结构还存在中程有序结构,这种中程有序结构与Cu₆Sn₅有序团簇相关。此外,在液态Sn-3.5Ag钎料中只发现了短程有序,而Sn-3.5Ag-0.7Cu熔体在260℃和330℃时除存在短程有序外还存在中程有序,此时的中程有序同样和Cu₆Sn₅团簇相关,说明Cu的加入增加了熔体中有序结构的尺寸和数量。随着温度的升高上述Cu₆Sn₅相关团簇遭到破坏,熔体中的中程有序结构消失。由上述结果可知,在钎焊温度下,熔融无铅钎料合金中将可能存在尺寸较大的有序团簇甚至是中程有序结构,而随着钎料中合金元素含量的变化,有序团簇的尺寸和数量均会产生变化,这将对钎焊界面反应产生影响。其次,利用高温粘度仪测量了Sn-xCu和Sn-3.5Ag-xCu钎料熔体的粘度。发现随着温度的升高,钎料合金的粘度值整体上呈下降的趋势,但存在明显的不连续性,均可分为低温区和高温区。通过Arrhenius方程计算了各温区内的粘流活化能ε和流团尺寸ν_m,结果表明钎料熔体在低温区和高温区之间的温度范围内发生了结构转变,这与高温X射线衍射的结果相一致。钎料熔体中ν_m值的差异必然会引起钎焊界面反应速率的不同。同时还利用Sn-xCu的粘度值计算了对应温度下的表面张力,计算结果与文献报道的结果较为接近,此外还通过Sn-xCu与Cu基板之间的润湿性实验验证了计算结果的正确性,这为获取无铅钎料合金表面张力数据提供了新的途径。研究表明无铅钎料合金的粘度和表面张力均为液态结构敏感量,其变化与液态结构的变化密切相关。随后,本文研究了Sn-xCu/Cu（Ni）和Sn-3.5Ag-xCu/Cu接头的钎焊界面反应。在钎料合金与Cu基板反应时,钎料中Cu含量的增加对界面IMC颗粒的粗化和生长起到加速作用,这与液态钎料中Cu₆Sn₅有序团簇的尺寸增加和数量增大相关。随着Cu含量的增加,Sn-xCu/Ni接头的界面产物由(Ni_xCu_1-x)₃Sn₄相逐渐转变为(Cu_xNi_1-x)₆Sn₅相,(Cu_xNi_1-x)₆Sn₅ IMC层的生长速率由钎料中Cu₆Sn₅的体积分数所决定。最后,由于无铅钎料合金元素与基板金属层（Cu和Ni）之间的界面反应纷繁复杂、数据分散,而合金元素的种类和含量对钎焊界面反应又存在重大影响,同时随着电子产品日趋小型化,焊点的尺寸也逐步减小,外来元素的引入,如通过镀层金属的溶解扩散,将很容易改变焊点钎料的原始成分,使钎焊界面反应变得更加复杂,甚至是难以控制,因此本文从钎料液态结构的角度分析和预测了合金元素对界面IMC类型、形貌和生长行为的影响。更多还原

【Abstract】 At present,the research of lead-free solder alloys has been widely concerned around the world,and certain progress and achievement have been reached.Among the current solder alloy systems,Sn-Cu,Sn-Ag and Sn-Ag-Cu become the focus of scientific research and commercial development.In the application of lead-free solders,the interfacial reaction is one of the key issues that affect the quality of soldering and the reliability of the joint.During soldering,the solder must experience from the solid state to the liquid state then again to the solid state,while during the reaction stage the solder is always at the liquid state.Thus,to study the liquid structure of the solder alloys,to discover the correlations between the liquid structure and the interfacial reaction during soldering,will have a significant effect on understanding the growth mechanism of interracial intermetallic compound（IMC） and controlling the growth rate of IMC.In this dissertation,two kinds of lead-free solders,namely Sn-xCu（x=0.7,1.5,2） and Sn-3.5Ag-xCu（x=0,0.7,1.5）,were chosen.First,the diffraction data of the solders were obtained by using a high temperature X-ray diffractometer,and then the liquid structure of the solders was calculated and analyzed.Only short rang order（SRO） structures were detected in liquid Sn-0.7Cu and Sn-1.5Cu solders,while there existed not only SRO structures but also medium rang order（MRO） structures in liquid Sn-2Cu solder at 260℃and 330℃.The MRO structures in Sn-2Cu melt were related to Cu₆Sn₅ ordered clusters.Also in Sn-3.5Ag melt only SRO structures were found.While MRO structures were detected in Sn-3.5Ag-0.7Cu melt at 260℃and 330℃besides the SRO.Such MRO structures were still related to Cu₆Sn₅ clusters indicating the size and amount of the ordered structures were increased with the addition of Cu.However with increasing temperature the before-mentioned Cu₆Sn₅ type correlative clusters were destroyed.As a result,the MRO structures disappeared.According to the previous results,it is clear that at the soldering temperature large ordered clusters even MRO structures will exist in lead-free solder melt,and the size or the amount will be changed with the variation of the alloying element in the solder,which can accordingly affect the soldering reaction.Secondly,the viscosity of Sn-xCu and Sn-3.5Ag-xCu solders was measured using a torsional oscillation viscometer.For all the melts the viscosity decreased with increasing temperature,however,there was obvious discontinuity.So two segments,namely a low temperature zone and a high temperature zone,were found correspondingly.The activation energyεand the unit volume of flow Vm were obtained according to Arrhenius equation.It was found that the anomalous variations of viscosity had a direct relation with the transition of the liquid structure,which is in good agreement with the results of high temperature X-ray diffraction.The difference in v_m of the solder melts will consequentially result in the different rate of interfacial reaction.At the same time,the surface tension calculated using the measured viscosity values was close to the reported value,and the results were also checked by performing the wetting test between the solders and the Cu substrates.This confirms the present method is quite reasonable to obtain surface tension values for solder alloys.Both viscosity and surface tension are closely related to the liquid structure of the solder alloy.Then the interfacial reactions of Sn-xCu/Cu（Ni） and Sn-3.5Ag-xCu/Cu joints during soldering were studied.When solders were reflowed with Cu substrates,the ripening process and the growth were accelerated by increasing Cu content.This was concerned with the increment of size and amount of Cu₆Sn₅ clusters in liquid solders.For Sn-xCu/Ni joints,the interfacial reaction product translated from(Ni_xCu_1-x)₃Sn₄ to(Cu_xNi_1-x)₆Sn₅ with increasing of Cu,and the growth rate of(Cu_xNi_1-x)₆Sn₅ IMC layer was controlled by the volume fraction of Cu₆Sn₅.Finally,the interfacial reactions between the lead-free solder containing elements and the metallization layers（Cu and Ni） are very complex,and the kind and the content of alloying elements have a great effect on the interfacial reaction.Furthermore,as the size of solder joint becomes smaller and smaller with the miniaturization of electronic products,the original composition of the solder joint can be changed easily by the introduction of extraneous elements,for example through the dissolution and the diffusion of the metallic layer,which leads to the interfacial reaction more complex and sometime even hard to control.Therefore from the viewpoint of liquid structure the effect of alloying elements on the type,morphology and growth behavior of the interfacial IMC was analyzed and predicted in this dissertation.更多还原