基于薄箔自蔓延反应的焊料互连机理研究

The soldering process based on foil self-propagating exothermic reaction has shown great prospect to solve the issues when bonding materials or components with thermal sensitive element or thermal mismatch materials for its special localized high-temperature, high-speed heat source, higher heating/cooling rate (more than 10^6 ºC/s) and smaller heat affected zone. However, as this localized high power heat released from the self-propagating reaction causes rapid heating/cooling of solder alloys and large temperature gradient in joint, the soldering process is under highly unsteady conditions, where the melting, wetting, filling and solidification processes all finished within a very short period (millisecond level) so that the reaction, nucleation as well as the crystallization among elements in solder alloys and substrates are freezed at the initial stage. These situation in self-propagating soldering causes the unique bonding morphology and soldering mechanism different from traditional process, especially the diffusion and reaction between elements, under unsteady condition. Therefore, the soldering process based on foil self-propagating exothermic reaction will be implemented, and finite element simulation and experiment will be used to study the heat cycle. Then, the heat cycle curve will be used to analyze the joining process combined with microstructure characterization. This research will focus on the unsteady solidification and crystallization process and the mechanism of wetting and interfacial reaction of solder alloys under such self-propagating heat source, and explore the the formation mechanism of different organizations and microstructures, clarify the influence of each processing parameters on the reliability of joints. And finally, this research will provide theoretical and experimental foundation for the comprehension of the soldering mechanism under highly-unsteady self-propagating conditions and thus promote the application of self-propagating soldering in the field of electronics packaging.

以薄箔自蔓延反应产热为热源的焊料互连由于其热量高度集中、温度高、移动速度快的热源特点，升/降温速度高达10^6 ºC/s，热影响区小，能解决热失配、热敏感材料或器件的封装互连问题。然而过高的升/降温速度和温度梯度导致反应互连过程的高度非稳态，焊料在极短时间（毫秒级）内完成熔化、润湿铺展及凝固结晶，各种过程都不能充分进行；其独特的热循环使互连组织形貌及其形成机理不同于传统封装互连。本项目拟进行薄箔自蔓延反应焊料互连，利用有限元模拟结合试验进行互连热循环研究；结合热循环曲线、合金相图和互连微观组织，分析互连过程，重点研究高度非平衡条件下焊料的熔化、凝固结晶过程以及在互连界面的润湿铺展和界面反应机理，探求各微观组织结构的形成机制与机理，进而弄清各工艺条件对互连可靠性的影响规律，最终为建立非平衡条件下的焊料互连理论及拓展薄箔自蔓延反应焊料互连在电子封装中的应用奠定理论和实验基础。

高集成度、高性能、多功能的小型化电子器件是电子、电力、通讯、汽车、传播、航空、航天、石油化工、军工等多种行业或领域发展的关键。这类器件通常是将具有不同功能的微芯片或微机电系统（MEMS）集成在一个电子系统中，即需要在有限的空间或者基板上同时完成各种由不同材料、加工工艺制得的器件的封装互连。然而，这些互连工艺技术都需要加热整体封装结构；当需要连接含有热失配、热敏感材料的元件或器件时，器件内部的热敏感元件和材料容易受到损伤。以Al/Ni自蔓延燃烧反应为基础的自蔓延燃烧反应互连技术可以解决此类互连问题。本项目针对Al/Ni薄泊自蔓延反应焊料互连进行了系列研究工作:首先通过实验和模拟手段对薄箔自蔓延反应热源作用下的焊料互连热循环过程进行了分析，建立了自蔓延反应时不同互连结构的有限元分析模型，得到了互连结构关键点和界面的温度循环曲线，利用该曲线，得到了不同条件下焊料熔化区的厚度，由此可以帮助选择芯片厚度、焊料厚度和预热温度，帮助指导互连结构尺寸设计和互连工艺制定；进一步结合温度循环曲线对在自蔓延高速热源下的界面反应行为及焊料凝固结晶组织进行了研究，发现不同类型焊料中均出现常规回流焊中未出现的显微组织，焊料的晶粒细化明显，凝固过程中焊料组织出现定向生长，偏析现象显著降低，增强相分布更均匀，互连接头性能提高，界面IMC（纳米级层状结构）长大不明显；最后完成了对自蔓延互连工艺的关键参数的优化及可靠性研究。项目研究将为多材料和热敏感器件提供一种新的互连方案，为高度非平衡凝固的研究提供借鉴。