基于石墨烯扩散阻挡层的微焊点界面扩散及演变机理

The high-density and miniaturization trends of the micro electronic components aggravate the loads on the micro solder joints, which work as the electrical connection parts. One of the key factors of improving the reliability of the solder joints as well as the components is to suppress the coarsening and brittleness of the interfacial intermetallic compounds (IMC). To solve this problem, graphene coated copper substrate (G-Cu) fabricated by chemical vapor deposition (CVD) was supposed to be the soldering substrate in this project. The interfacial coarsening might be suspended by suppressing the diffusion of the elements at the interface by the graphene layer in the micro solder joint . The commercial SAC305 solder, which has been widely applied in this area, is used as the soldering material. Fundamental researches will be carried out on the SAC305/G-Cu soldering interface. Basic problems will be investigated, including: the effects of the thickness of the graphene layers on the wettability, interfacial reactions, and connection properties of the soldering interface; establishing the physical models of the interfacial structure and dynamic constitutive equations describing the IMC evolution at liquid-solid and solid-solid interfaces; the effects of graphene layers on the growth behavior and electromigration of the interfacial IMC under thermal-electrical coupling condition; the suppressing mechanism of graphene layers on the interracial diffusion; and the evolution mechanism of the interfacial IMC suppressed by the graphene layers. The research achievements will provide theoretical basis to develop the material and the structure of the new-generation substrates for lead-free soldering.

微电子器件高集成、微型化趋势加剧了作为电气连接的微焊点负荷，抑制界面金属间化合物(IMC)粗化所导致的界面脆化成为提升微焊点和器件可靠性的关键之一。针对此问题，本项目拟采用化学气相沉积法(CVD)制备的铜基石墨烯基板(G-Cu)进行钎焊连接，通过微焊点界面处的石墨烯层抑制由于界面元素扩散所导致的界面恶化。以本领域应用最广泛的SAC305为钎料，开展SAC305/G-Cu钎焊连接的相关基础研究。分析添加石墨烯层厚度对钎焊过程中钎料润湿铺展特性、界面反应、连接性能的影响机制；构建钎焊界面在液-固、固-固界面条件下的界面结构物理模型与IMC生长动力学本构方程；研究石墨烯层对钎焊界面IMC在温度、电流两场作用下生长行为与电迁移特性的影响机制；阐明石墨烯层对界面元素扩散的阻挡机制；揭示石墨烯扩散阻挡层作用下的界面IMC演变机理。项目研究成果对探索新一代无铅软钎焊基板材料与结构提供理论基础。

随着电子信息产业高速发展，高集成、高性能、小型化成为电子产品的主流发展趋势。作为芯片与基板间热、电、力等方面互连载体的焊点尺寸随之减小，相应其所承载的负荷则急剧增大。微焊点的性能及可靠性直接影响电子产品的整体寿命，因此当今微电子互连技术成为影响电子信息产业发展的技术瓶颈。钎料与基板之间所形成界面金属间化合物(IMC)的粗化极大地降低了微焊点的可靠性。为了抑制界面IMC在焊接与时效过程中的过度生长，本项目以熔炼的方式将Ni元素添加到SAC305钎料中，并使其在普通铜板(Cu)、高温处理铜板(H-Cu)和石墨烯铜板(G-Cu)三种基板上进行润湿铺展形成微焊点。对无铅焊点的界面IMC层演变规律和体钎料的力学性能进行研究分析，为其进一步的实际运用提供充分的理论依据。主要结论如下：1.微量的Ni元素可以提升体钎料的润湿性能；对比钎料在Cu与G-Cu的润湿性能，发现在G-Cu基板上的润湿性能较好，基板上的石墨烯镀层可以提升钎料润湿性能。2.G-Cu基板表面上的石墨烯镀层对焊点体钎料的微观组织产生了细化的作用。随着钎料中Ni含量的增加，焊点体钎料中的β-Sn数量急剧上升，共晶组织的面积减小。3.对比G-Cu与Cu基板的界面IMC的厚度，发现G-Cu基板的IMC厚度较低，表明基板石墨烯镀层可抑制界面IMC的生长。4.随着高温时效时间的增加，界面IMC的厚度也在逐渐增加。石墨烯镀层可以抑制时效过程中元素的扩散，降低IMC的生长速率。5.基板表面的石墨烯镀层在焊接过程中部分扩散到体钎料中，从而对焊点体钎料的硬度产生影响。通过本项目的开展，证实了石墨烯二维结构材料在电子封装互连结构中应用的可行性，明确了石墨烯层在钎焊界面反应与连接过程中的作用，阐明了石墨烯层对界面元素扩散的阻挡机制，揭示了石墨烯扩散阻挡层作用下的界面IMC演变机理，为研究发展新一代微电子封装基板材料与结构提供理论基础。