非均质双相基板锡焊点非均匀反应性润湿机制及其可靠性研究

The nonuniform reactive wetting phenomenon between liquid Sn-based solders and heterogeneous dual-phase metallic subsrate results in numerous microgrooves on the substrate surface, which can enhance the wettability between liquid solder and substrate. This will benefit the application of solder/dual-phase substrate joints in the electronic packaging. Nevertheless, the mechanism of nonuniform reactive wetting and the influence of it on the reliability of solder/dual-phase substrate joints are still unknown. Thus, the present project mainly focus on the fundaments of scientific issues of wetting mechanism and reliability of Sn/Cu-Co dual-phase substrate joint. The mechanism of nonuniform reactive wetting will be revealed by gaining the wettability between liquid Sn and dual-phase substrate through the sessile drop technique. The interfacial reaction, microstructure and growth kinetics of intermetallic compound (IMC) will be studied. Moreover, the shear strength, crack propagation and fracture mechanism of solder joint will also be investigated. Based on the interfacial energy of solder joint, a theoretical model which is used to quantitatively describe the wetting behavior between liquid Sn and dual-phase substrate will be established. The synergistic effect of the ratio and micro-scale of two phases in substrate on the wettability and reliability of solder joint will be illuminated by combining the experimental and theoretical results. As a result, the wettability and reliability of solder joint can be adjusted by controlling the microstructure of the dual-phase substrate. The project will contributes to the design and manufacture of the solder/dual-phase heterogeneous subsrate interconnects with high reliability. It is of scientific significance and application value.

液态锡基钎料与非均质双相金属基板的非均匀反应性润湿现象促使基板表面形成大量微沟槽，从而增强液态钎料与基板的润湿性能，这一现象有利于双相基板在电子封装领域的应用。然而，液态钎料与双相基板的非均匀反应性润湿机制及其对焊点可靠性的影响规律并不明确。所以本项目拟围绕Sn/Cu-Co双相基板焊点润湿机制及可靠性的基础科学问题展开研究。以静滴法获取液态锡与双相基板的润湿性能来揭示非均匀反应性润湿机制；探究焊点界面反应、微观结构及金属化合物（IMC）生长动力学；明晰双相基板锡焊点剪切强度、裂纹扩展规律及断裂机理；从焊点界面能出发，建立一套定量描述液态锡与双相基板润湿行为的理论模型，并结合实验结果阐明基板双相比例及其微观组织尺度对焊点润湿规律及其可靠性的协同效应，有望通过控制基板微观组织实现对焊点润湿性及可靠性的调控；项目的实施有助于高可靠性双相非均质基板锡焊点的设计与制造，具有较大的科学意义和应用价值。

本项目选用了Sn3.0Ag0.5Cu（SAC305）无铅钎料，制备了高质量的Cu-50Co（50 wt.% Co）和Cu-50Fe（50 wt.% Fe）两种双相合金基板，研究钎料与不同基板形成焊点的界面微结构与金属间化合物（IMC）的演化过程。在温度为290°且不同时间的钎焊过程中，SAC305/Cu界面形成的化合物为Cu3Sn和Cu6Sn5，SAC305/Cu-50Co界面生成(Co,Cu)Sn3和(Cu,Co)6Sn5，SAC305/Cu-50Fe界面则为(Cu,Fe)6Sn5和FeSn2。SAC305/Cu-50Co和SAC305/Cu-50Fe的界面IMC呈现奇特的锯齿状形貌，而SAC305/Cu界面化合物形貌表现为光滑连续。比较三种焊点界面化合物的晶粒形貌，SAC305/Cu界面化合物主要为呈球状的Cu6Sn5晶粒，SAC305/Cu-50Co界面(Cu,Co)6Sn5和(Co,Cu)Sn3化合物分别为细针状和棍棒状的细小晶粒，钎焊后期(Co,Cu)Sn3表现出棱柱状的堆叠形貌；SAC305/Cu-50Fe界面(Cu,Fe)6Sn5晶粒为棱柱状，FeSn2呈细小颗粒状。本项目还研究设计了SAC305/Cu、SAC305/Cu-50Co和SAC305/Cu-50Fe三种焊点进行恒温150°不同时长的时效实验。结果显示，在固态时效过程中，焊点界面化合物的成分与液态钎焊过程中成分一致。超声辅助焊接实验的结果表明，在液-固冶金反应发生时引起的空化和声流效应能够细化组织晶粒，明显降低钎料与基板之间的润湿角。焊点的剪切实验表明短时间内的超声作用可以有效提高焊点的最大剪切强度，但过长时间的超声作用将导致焊点最大剪切强度下降。目前针对本项目已经取得的一系列成果，共发表SCI期刊论文57篇，授权专利一篇。