13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- 3. Results and discussion Fig. 2 (a) Photograph of the sample (b) SEM image of the fabricated nanowire array (c) SEM of the nanowire array after the parylene coating As can be seen in figure 2a, it was easy to distinguish the fastener area from the Au film via their surfaces because the former became red in color. Scanning electron microscopy (SEM) observation (figure 2b) indicated that copper nanowire array grew on all the red area and the length of the nanowire array was uniform in most areas. From figure 2c, many relative dark shells around the bright wires could be observed. Because the parylene is non-conductive, it is darker than the copper in SEM image. The thickness of the shell was measured to be about 50nm. The voltage-current (U-I) curve of interconnected fasteners is shown in figure 3b. The solid line in the figure was obtained through linear fitting of the measured values. Typical Ohmic contact performance was observed and parasitic resistance of 0.82 Ω can be extracted from the slopes of the fitted line. This result is possible to be used as the electrical bonding in surface mount. Figure 4 shows photograph of surface fasteners sustaining a weight of 500g in the shear direction. This bonding strength corresponded to the adhesion strength of 50 KPa. The purpose of our research is to develop a new mechanical and electrical room temperature bonding in surface mount. Regarding to the room temperature bonding or solder in surface mount, there are some design guidelines about the ratio between the component’s weight and the bonding area. According to the standard value for second side reflow mounting (R=30g/in2)[14]. If we consider this weight-area ratio to be R=50g/cm2, which is more than ten times than the standard value. The bonding strength (S=50kPa) can withstand an acceleration of a=S/R=100N/kg>10*g (g=9.8N/kg is the acceleration of gravity). This result means that this room temperature bonding technique can be used in most equipment. Fig. 3 (a) Schematic of four-point probe measurement (b) Measured U-I curves of the bonding
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