Advanced Analysis Center, Korea Institute of Science & Technology, Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Republic of Korea.
Microsc Microanal. 2013 Aug;19 Suppl 5:49-53. doi: 10.1017/S1431927613012312.
We investigated the microstructural evolution of Sn(96.4)Ag(2.8)Cu(0.8) solder through in situ heating transmission electron microscopy observations. As-soldered bump consisted of seven layers, containing the nanoeutectic lamella structure of AuSn and Au₅Sn phases, and the polygonal grains of AuSn₂ and AuSn₄, on Au-plated Cu bond pads. Here, we found that there are two nanoeutectic lamellar layers with lamella spacing of 40 and 250 nm. By in situ heating above 140°C, the nanoeutectic lamella of AuSn and Au₅Sn was decomposed with structural degradation by sphering and coarsening processes of the lamellar interface. At the third layer neighboring to the lamella layer, on the other hand, Au₅Sn particles with a zig-zag shape in AuSn matrix became spherical and were finally dissipated in order to minimize the interface energy between two phases. In the other layers except both lamella layers, polycrystal grains of AuSn₂ and AuSn₄ grew by normal grain growth during in situ heating. The high interface energy of nanoeutectic lamella and polygonal nanograins, which are formed by rapid solidification, acted as a principal driving force on the microstructural change during the in situ heating.
我们通过原位加热透射电子显微镜观察研究了 Sn(96.4)Ag(2.8)Cu(0.8)焊料的微观结构演变。在镀金铜焊盘上，原始焊点由包含 AuSn 和 Au₅Sn 相纳米共晶层结构以及 AuSn₂和 AuSn₄多晶的七个层组成。在这里，我们发现有两个具有 40 和 250nm 层间距的纳米共晶层。通过在 140°C 以上的原位加热，AuSn 和 Au₅Sn 的纳米共晶层通过球形化和层间界面粗化过程发生结构降解而分解。另一方面，在与层状层相邻的第三层上，AuSn 基体中的锯齿状 Au₅Sn 颗粒呈球形，最终消散，以最小化两相之间的界面能。在除了两个层状层之外的其他层中，AuSn₂和 AuSn₄的多晶晶粒通过原位加热时的正常晶粒生长而长大。纳米共晶层和由快速凝固形成的多边形纳米晶粒的高界面能是原位加热过程中微观结构变化的主要驱动力。
