13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- were ion milled to electron transparency at room temperature by a Gatan Model 691 precision ion polishing system (PIPS). All TEM specimens were examined in a 300 kV Tecnai F30 (FEI Field Emission Gun TEM with LaB6 filament). STEM and energy dispersive X-ray (EDX) spectroscopy microanalysis were used for chemical analysis. 2.3. Tensile experiment under quasi-static loading In order to characterize the bonding strength, each bonded chip was diced into 4 mm × 4 mm specimens by an automated dicing saw. Before the tensile test, all samples for tensile tests were examined under an optical microscope with 50× objective lens to exclude defective ones. The specimens were attached to aluminum jigs with glue for the tensile test. The bonding strength was measured by a tensile pulling machine (GATAN Microtest 2000) and the specimen under test was pulled perpendicular to the bonding interface until its rupture. The test pulling speed was 1 mm/min, and the pulling speed and the data acquisition were controlled by a personal computer. In these pulling tests, it was found that the maximum failure loads of these specimens were less than 5 N, and the specimens were easily damaged when they were fixed to rigid fixtures of the test machine. The alignment of the test studs is of critical importance because small deviations will induce bending moments which can cause premature failure of the test sample [13]. To improve the alignment of test samples and to avoid the early failure caused by the force from sample installation, a special fixture was designed with flexible steel wire strand, as shown in Figure 4. Figure 4. Schematic of fixture for tensile tests 3. Results and discussion 3.1. Fractures in bonded specimens When all the bonding specimens were examined under optical microscope, fractures were found in some of the specimens, as indicated by white arrows in Figure 5. The fractures occurred in the glass side at the corner of the mesas, and many of them were found in the samples anodically bonded at higher bonding temperature. During the process of anodic bonding, when the bonding temperature was larger than 350°C, the fractures of this type were easily found in some specimens. This kind of fractures seldom occurred in the specimens bonded at the temperature of no more than 350°C. The reason for the occurrence of these fractures is the different thermal expansion coefficient with Pyrex
RkJQdWJsaXNoZXIy MjM0NDE=