Models for Initiation and Growth of Microwelds in Ultrasonic Bonding

** 超声波连接技术对于微电子、汽车和航空航天部件、特种服装和超声波增材制造的制造非常重要。超声波焊接是一种低温、低成本的焊接工艺，适用于异种材料的连接。超声波连接成功地用于大尺寸和小尺寸，例如分别用于金属板连接和微电子引线键合。对于超声连接向更大（汽车）和更小（纳米技术）领域的改进没有根本限制。然而，超声波连接面临着实际的限制和挑战。例如，在汽车领域，开发一直集中在证明超声波连接对于较厚板材、较硬材料以及不同轻质材料（如Ti、Al、Mg或复合材料）的组合的可行性。微电子引线键合中的超声波接合尚未克服的挑战是由于向纳米领域的小型化、低成本材料的使用以及具有降低的刚度的薄管芯封装而出现的。拟议的研究旨在通过发现预测的理论模型，进一步了解超声连接。这些模型可用于改进和加速超声波连接工艺的设计，以克服现有的挑战。目前，只有严格简化的假设，才有可能描述超声波连接的过程物理。不幸的是，这导致接头质量的低精度预测。** 本研究中的新方法将描述微焊接对粘结质量的影响。在超声焊接过程中，微焊缝在结合区成核，并导致强结合的成功生长。然而，微焊缝如何生长成强键的确切机制目前尚不清楚。拟议的研究将通过基于基础物理学的方法来解决这种知识的缺乏。这将揭示微焊缝形成机制，并导致改进的模型和更准确的预测。* 实验工作包括在微电子引线键合（低功率，130 kHz超声）和芯片贴装（高功率，20 kHz超声）机器上开发的超声接合工艺，该机器可供大学研究小组使用。测量过程结果并用于确定理论模型的参数，这些参数将在理论工作中开发。在本研究项目中接受培训的学生将在电子组装技术，超声波焊接和微焊接技术，分析方法，项目规划，领导力和沟通方面具有很高的技能。

******Ultrasonic joining technology is important for the manufacturing of microelectronics, automotive and aerospace components, speciality clothing, and ultrasonic additive manufacturing. Ultrasonic joining is a low temperature and low cost process and suitable for joining parts made from dissimilar materials. Ultrasonic joining is successfully used in large and small dimensions e.g. for sheet metal joining and microelectronic wire bonding, respectively. There is no fundamental limit to improvements of ultrasonic joining towards even larger (automotive) and smaller (nanotechnology) domains. However, ultrasonic joining is facing practical limitations and challenges. In automotive for example, development has been focusing on proving ultrasonic joining's feasibility for thicker sheets, harder materials, and combinations of dissimilar lightweight materials such as Ti, Al, Mg, or composite materials. Challenges not yet overcome for ultrasonic joining in microelectronic wire bonding arise due to miniaturization towards the nano domain, the use of low cost materials, and thin die packages with reduced stiffness.*********The proposed research aims at furthering the knowledge of ultrasonic joining by discovering predictive theoretical models. Such models can be used to improve and accelerate the designs of ultrasonic joining processes that overcome existing challenges. Currently, only with severely simplifying assumptions is it possible to describe the process physics of ultrasonic joining. Unfortunately, this results in low accuracy predictions of joint quality. *********Novel approaches in this research will describe the effect microwelds have on the bond quality. Microwelds nucleate in the bond zone during ultrasonic joining and lead to successful growth of strong bonds. However, the exact mechanisms how microwelds growth into strong bonds is currently unknown. The proposed research will address this lack of knowledge with a methodolgy based on fundamental physics. This will shed light on microweld formation mechanisms and lead to improved models and more accurate predictions. *********The experimental work consists of ultrasonic joining processes to be developed on microelectronic wire bonding (low power, 130 kHz ultrasound) and die attach (high power, 20 kHz ultrasound) machines available to the research group at the University. Process outcomes are measured and used to determine parameters of the theoretical models which will be developed in theoretical work. Students trained in this research project will be highly skilled in electronics assembly technologies, ultrasonic welding and microwelding technologies, analytical methods, project planning, leadership, and communication.