3D封装多次回流Sn/Cu钎焊界面反应及控制机制

In the current generation of 3D electronic packaging characterized by the miniaturization of electronic products, multiple reflows based on Sn/Cu solders are generally required during soldering. Most of the research works hither to, simply have been regarding the multiple reflow process as a long time soldering reaction consequently resulting in deduction of some inaccurate or impractical mechanisms for interfacial IMC growth. The dynamic relationship between interfacial reaction mechanism and composition evolution in liquid solder for each solder reflow cycle, which is a key scientific issue, has been ignored in the existing research works. By this viewpoint, the applicant prepares to investigate the precise reaction mechanism of liquid/solid interfacial IMC in every stage of multiple reflows utilizing the real-time imaging technology of Shanghai Synchrotron Radiation Facility (SSRF) as well as experimental method of high pressure air blowing. The analysis of the concentration variation in solder with reflow times and its effect on IMC dissolution in heating as well as IMC growth and evolution in holding temperature and cooling procedures; investigation of mechanism for impact of solder size and nano particles on interfacial reaction; knowledge of mechanism aided by numerical simulation for temperature field distribution inside the solder bump; will be holistically used to finally establish Sn/Cu interfacial reaction model during multiple reflows on the basis of the composition regulation in tin solder and thereafter develop a practical technique to forecast the interfacial reaction in 3D electronic packaging as well as an effective tool to improve the IMC growth of multiple reflow solder joints.

电子产品微型化推动封装技术由二维（2D）向三维（3D）发展，而采用Sn/Cu钎焊体系并经多次回流工艺是3D封装普遍应用的技术。现有研究大都将多次回流简单归结为一次回流焊处理，所获得的多次回流界面反应机制与实际偏差较大。基于此，申请者从每次回流后焊料成分变化导致界面反应规律发生改变，这一未被关注的核心问题出发，利用上海光源同步辐射实时成像和高压空气吹扫的实验手段，对多次回流焊各阶段液固界面反应机理进行分解剖析；重点关注每次回流焊点成分变化及对加热阶段界面金属间化合物(IMC)溶解，回流和冷却阶段IMC生长及控制因素的影响；明确多次回流焊点“尺寸效应”及纳米颗粒调控界面反应的机理；结合多次回流焊点温度场数值模拟；最终建立起基于焊点成分变化规律的Sn/Cu多次回流焊界面反应模型，并发展出实用化的3D封装多次回流焊界面反应预测技术及调控多次回流焊界面IMC生长的有效工艺手段。

电子产品微型化推动封装技术由二维（2D）向三维（3D）发展，而多次回流工艺是3D封装普遍应用的技术。现有研究大都将多次回流简单归结为一次回流焊处理，所获得的多次回流界面反应机制与实际偏差较大。应用同步辐射实时成像及高压吹扫技术，分离多次回流钎焊过程各个阶段，并结合相应模拟手段，深入研究钎料合金成分、回流工艺参数、气泡缺陷、焊点尺寸下钎焊液固反应过程界面金属间化合物（IMC）生长机理及动力学，清晰地揭示出各Sn/Cu体系钎焊界面反应过程，并建立多次回流界面IMC生长模型。.获得主要结论如下：.1、多次回流保温阶段，界面IMC生长控制机制逐渐从Cu晶界扩散转变为体扩散，动力学时间指数由1/3趋近1/2；冷却阶段，界面IMC受Cu沉积作用快速生长，动力学时间指数为1；再加热阶段，Cu溶解度改变使界面IMC发生部分溶解，动力学时间指数为1，与冷却阶段互逆；建立Sn/Cu体系多次回流界面IMC生长物理模型。.2、多次回流中，焊料中 Cu 浓度随回流次数波动增加，与 IMC 生长和溶解密切相关；Cu 浓度的变化会导致 IMC生长速度、焊点的维氏硬度和熔点在多次回流中的波动。.3、Sn-xCu/Cu焊点中Cu浓度升高，界面IMC生长速率增大，晶界扩散对界面IMC生长贡献相对减小；Sn-xAg/Cu焊点中，Ag3Sn纳米颗粒吸附在界面IMC晶粒表面，提高晶界扩散对界面IMC生长的贡献，且Ag3Sn尺寸越小、分布越弥散，效果越明显；TiO2纳米粒子能够抑制多次回流过程中界面IMC的生长，且温度越低，Sn-xTiO2/Cu焊点中TiO2含量越高，抑制效果越强。.4、Sn/Cu及Sn-0.7Cu/Cu焊点尺寸减小，液钎中Cu浓度增大，IMC层厚度增大。Sn-3.5Ag/Cu焊点受Cu浓度和Ag3Sn颗粒的双重作用，尺寸减小，IMC层厚度先增大后减小。