Fundamental Investigation into the Mechanism of Ultrasonic Wedge-Wedge Bonding through Change of Topography

尽管超声引线键合技术已经广泛应用了半个多世纪，但其潜在的机理仍然不完全清楚，这阻碍了进一步的改进。拟议的项目将致力于研究未揭示的机制以及键合参数对它们的影响。具体地说，摩擦和软化阶段是项目的重点。这些相在氧化物的去除和微焊缝的形成中起着重要的作用，决定了键合的速度和强度。焊丝或衬底表面的氧化层是形成键合的主要障碍。摩擦相和软化相都影响氧化物从纯金属表面的剥离和剥离的氧化物的迁移过程。由于尺寸极小，很难观察到键合过程中的天然氧化层和分散的氧化物，特别是对于实时观察。在拟议的项目中，将利用微粒子和不透明层来模拟天然氧化物。通过分步实时观测，推断出氧化物的去除路径。衬底的粗糙度为微焊缝的形成提供了位置。然而，对这些粗糙度的软化效果尚不清楚。在本项目中，通过构造衬底，分析不同位置的粗糙度变形，从而推断软化效应。此外，为了获得更多关于焊接强度的信息，还将研究焊接过程中微焊缝面积的增长和微焊缝的平均强度。在焊接过程中，氧化物-金属接触区、金属-金属接触区和微焊缝区域总是变化的。复杂的动态粘接界面为了解粘接速度和强度设置了障碍。为了实时研究复杂的界面，将开发一种新型的高分辨率分布式传感器阵列，并将其嵌入到衬底中。通过这种方法，可以测量界面不同位置的局部切向力和法向力。传感器阵列的输出将提供大量关于局部变化的信息，特别是局部微焊缝的形成和断裂的信息。在整个项目中，将采用试验设计(DOE)来分析工艺参数的影响。最后，将建立一个经验模型来预测界面随时间的变化，包括氧化物分布、衬底粗糙度、局部强度和整体强度。在以上分析的基础上，提出并评估了基板和焊丝上的新形貌，以提高键合速度和质量。所有这些结果都将从根本上深入了解粘合机制，填补该领域的空白。

Even since the ultrasonic wire bonding technique has been widely applied for more than half a century, the underlying mechanisms are still not completely understood, which prevents further improvement. The proposed project will be dedicated to investigate the unrevealed mechanisms as well as the influences of the bonding parameters on them. Specifically the friction and the softening phases are the focus points of the project. These phases play a significant role in oxides removal and microwelds formation and determine the bonding speed and strength.The oxide layer on the surface of wire or substrate is the main obstacle for the bonding formation. Both friction and softening phases affect the oxides removal process with regard to the detachment of oxides from pure metal surface and the transportation of the detached oxides. Due to the extremely tiny dimension, the natural oxide layer and the discretized oxides during the bonding process are hard to be observed, especially for real-time observation. In the proposed project, micro-particles and intransparent layers will be utilized for emulating the natural oxides. Through the step-wise and real-time observations, the removal paths of the oxides will be deduced. The substrate asperities provide locations for microwelds formation. The softening effect on these asperities, however, is unclear. In this project via structuring the substrate, the deformation of asperities at different locations will be analyzed so that the softening effect can be deduced. Furthermore, the microwelds area growth during the bonding process and the average strength of microwelds will be studied to obtain more information on the bonding strength.The oxide-metal contact regions, the metal-metal contact regions and microwelds regions are always changing within the bonding process. The complex dynamic bonding interface places an obstacle to the understanding of the bonding speed and strength. In order to real-time study the complex interface, a novel high resolution distributed sensor array will be developed and embedded in the substrate. By using this, the local tangential and normal forces at different locations of the interface will be measured. The output of the sensor array will provide large amount of information on the local changes, especially the local microwelds formation and breakage.Through the whole project, design of experiment (DOE) will be applied to analyze the influence of the process parameters. Finally, an empirical model will be established for predicting the changes at the interfaces over time, including the oxides distribution, the substrate roughness, the local strengths, and global strength. Based on the above analysis, new topographies on the substrate as well as on the wire will be proposed and evaluated so that a promotion of the bonding speed and quality will be gained. All of the results will provide a fundamental insight into the bonding mechanisms and close gaps in this field.