# In-Situ Observation of Adhesion Behavior During Ultrasonic Al Ribbon Bonding
## 3 Results
### In-situ Observation of the Fracture Process in Twist and Peel Test  
Figure 11 shows the video captures during the twist and peel test. The testing sequence is from (a) to (h) in Figure 11. It is important to observe the position and manner in which the fracture occurs, to confirm the positional relation of Areas A, B, and C. Area A is divided into A\({}_{1}\) and A\({}_{2}\) for explaining the fracture behavior. Area B is also classified into the three parts of B\({}_{1}\), B\({}_{2}\), and B\({}_{3}\). Once the rotating force was applied in a clockwise direction, the lower side of B\({}_{2}\) discolored to dark gray, as shown in Figure 11b. The upper side of A\({}_{1}\) and the lower side of A\({}_{2}\) were slightly blurry. A few white fine stripes appeared in C. Therefore, Areas A and C were not only in contact with the silica substrate but also experienced a chemical adhesion with the silica. The ribbon was observed rotating along the axis of a white area marked by the asterisk in Figure 11c. Area B\({}_{1}\) did not rotate at all and stood on the silica substrate, although partially peeled from the silica side. Conversely, B\({}_{2}\) and B\({}_{3}\) rotated. The central part of Area A began to appear behind the original area of B\({}_{2}\) and B\({}_{3}\); it was observed clearly with twisting, as shown in Figure 11c,d. Figure 11d is the video captured upon twisting by 40\({}^{\circ}\) in the clockwise direction (step 1 is complete). Figure 11e is the video capture at the beginning of step 2. When the Al  
Figure 10: In-situ observation results (video captures) of the bonding interface between Al ribbon and silica substrate obtained at \(F_{rate}\) = \(10^{3}\) fps. The bonding condition was \(F_{b}\) = 7 N and \(P_{u}\) = 4 W. Simultaneous measurement result of ultrasonic vibration amplitude is shown in Figure 3 (b–2): (**a**) \(t\) = 0 ms without ultrasonic vibration (US); (**b**) \(t\) = 1 ms immediately after introducing US; (**c**) Apparent bonded area increased at \(t\) = 5 ms; (**d**) Apparent bonded area decreased at \(t\) = 10 ms due to Al ribbon warping; (**e**) \(t\) = 20 ms; (**f**) Central belt zone began to be observed at \(t\) = 50 ms; (**g**) \(t\) = 100 ms; (**h**) \(t\) = 400 ms.  
ribbon was twisted in a counterclockwise direction, a portion of Area A appeared clearly as blackish gray in the central area. The belt zone (B\({}_{1}\), B\({}_{2}\), and B\({}_{3}\)) existed in front of Area A. Both of B\({}_{2}\) and B\({}_{3}\) were behind B\({}_{1}\). The final fracture due to peeling (step 3) occurred in the neighborhood marked by the asterisk. As shown in Figure 11g,h, a portion of B\({}_{1}\) almost remained on the silica substrate and appeared white, even after fracture. The peripheral edge of B\({}_{2}\) also remained on the silica side as a blackish gray marked as D, as observed in Figure 11g.  
The fracture process was as follows. Initially, Area C was broken, followed by Area A, and eventually Areas B\({}_{2}\) and B\({}_{3}\). Finally, Area B\({}_{1}\) was fractured. It was determined that the positional relation of each area in the direction normal to the bonded interface was Al ribbon/Area A/Areas B\({}_{2}\) and B\({}_{3}\)/Area B\({}_{1}\)/silica substrate. The island streaks combined with one another; however, but Area A did not change to Area B. Area B was formed by the interfacial reaction between Area A and the silica substrate [14,22].