# In-Situ Observation of Adhesion Behavior During Ultrasonic Al Ribbon Bonding
## 3 Results
### In-Situ Observation of Adhesion Behavior Obtained at a Frame Rate of \(10^{4}\) fps  
Figure 4 shows the change in the video captures obtained at \(F_{rate}=10^{4}\) fps with the bonding time, \(t\), under the bonding condition of \(F_{b}\) = 7 N and \(P_{u}\) = 3 W. Long slip marks due to initial ribbon shaking are observed in Figure 4a. 10-20 ms was required for the macro folding to complete. The apparent bonded width achieved was twice the tool width; however, the overall (apparent) bonded area does not widen after \(t\) = 20 ms. The striped pattern consisting of several island streaks was clearly observed at \(t\) = 30-50 ms, as shown in Figure 4b. The slip motion was observed even at the central area. The island streaks were dark gray and became longer with time. The number of islands increased; however, it did not appear to be copious. The appearance of the striped pattern did not change after \(t\) = 100 ms. The slip motion was scarcely observed at \(t\) > 100 ms. Both sides of the contact area appeared to repeat a touch and detach motion. No central belt zone was observed in the captures in Figure 4; however, something similar to a belt zone was vaguely observed in the video at \(t\) > 100 ms and it appeared translucent, approaching transparency. Figure 5 shows the surface roughness along the width of the Al ribbon and the video capture at \(t\) = 100 ms in Figure 4. Figure 5a shows the surface roughness measured, without the cut-off [14]. Figure 5b,c are the profiles after removing the wavelengths less than 10 \(\upmu\)m and 50 \(\upmu\)m, respectively. Figure 5c expresses the surface waviness in the transverse direction of the Al ribbon. The wavelength was roughly 120 \(\upmu\)m. The interval between the island streaks was about 60 to 140 \(\upmu\)m as shown in Figure 5d. The initial contact of Al ribbon on the silica surface was locally formed at the high peaks of the Al surface waviness. The island streaks were produced as a long footprint, at the interface between Al and silica. The peaks with a shorter wavelength, as shown in Figure 5b, had to be placed in contact with the silica sequentially in time. The footprints of the small peaks of surface roughness were not clearly captured by the high speed video camera. Figure 3: Change in ultrasonic vibration amplitude of tool head during ultrasonic bonding: (**a**) Under the bonding condition of \(F_{b}\) = 7 N and \(P_{u}\) = 3 W. (a–1) Result measured simultaneously with the video taken at \(F_{rate}=10^{4}\) fps. (a–2) Result measured simultaneously with the video taken at \(F_{rate}=10^{3}\) fps; (**b**) Under the bonding condition of \(F_{b}\) = 7 N and \(P_{u}\) = 4 W. (b–1) Result measured simultaneously with the video taken at \(F_{rate}=10^{4}\) fps. (b–2) Result measured simultaneously with the video taken at \(F_{rate}=10^{3}\) fps. Figure 6 shows the comparison between the video image (a), immediately before bonding terminates, and two still images, (b) and (c), after bonding (cooling to the room temperature). The schematic drawings of each image are illustrated in the bottom portion of Figure 6. The illumination differs between Figure 6b,c. Areas A, B, and C are defined in the bottom portion of Figure 6. In the still images, Area B is divided into B\({}_{1}\) and B\({}_{2}\). A part of Area C is detached from the substrate when unloading \(F_{b}\). The central belt zone is scarcely visible in image (a). However, the central belt zone is clearly observed in still images (b) and (c) captured at a low shutter speed of 1 ms. The correlation coefficients, \(r\), are calculated between the digital images boxed by yellow dotted lines, as shown in Figure 6. The \(r\)-values are 0.17 between (a) and (b), 0.12 between (a) and (c), and 0.67 between (b) and (c). The Al ribbon in image (a) leans slightly to the left; however, the image (a) is not treated with angularity correction. Central belt zones are not observed and all island streaks are not always visible in the image (a).