Bin Zhang’s research while affiliated with Corning Incorporated and other places

Cover glass in commercial handheld devices is now evolving from flat (2D) to curved (3D) shapes. For example, some commercial devices have utilized sled-shape cover glass, which partially covers long edges of the device. According to the patents published by key handheld manufacturers, we can expect more variety of 3D shaped cover glass for handheld devices in the market. In this study, we have focused on the reliability of 3D cover glass when it is dropped to a rigid surface. The key parameters under study are the corner/edge bend radius and angle of the cover glass, which determines the 3D shape of the cover glass. To achieve this goal, we developed a finite element model to simulate the drop of a handheld device with 3D-shaped glass. The model uses explicit algorithm to simulate the high speed impact on the device during the drop test. The glass performance was evaluated based on contact force between the glass and the ground and maximum principal stress in the glass. We showed that to avoid severe damage because of first impact between the glass and the ground, the bend angle of 3D glass has to be in the range between 0 and 45 degrees. For drop angles of 45 degrees and higher, with the proposed glass bend angle, the impact can be taken over by the edge of the back cover of the device. In addition, we showed that optimum glass bend radius is in the range of 3.8mm and larger. This is required to reduce stress in glass because of impact. The approach and conclusions from the current study can serve as a general guideline to improve the 3D cover glass reliability of a handheld device.

Cover glass reliability performance in a drop test is critical for handheld electronic devices. Handheld device drop test has limitations in measuring dynamic response on the device components which complicates the test control and data analysis. To supplement, design and improve the drop test we developed a full-scale modeling approach of a representative handheld device drop test. The device model includes all the major components such as: display, cover glass, rear cover, battery, printed circuit board/bracket, screws, adhesives, etc. The developed model explicitly simulates the device drop test, allowing us to measure mechanical parameters as function of process time for each of the device components. The numerical model was validated with the device drop test. In the current report we are focused on cover glass reliability. The cover glass performance was studied with respect to effects of adhesive materials on the rear side of the cover glass and the overall device rigidity. Using the model, we evaluated effects of each device component for the cover glass during drop. It was shown that significant cover glass reliability improvement in the device resistance against sharp indentation can be achieved if the glass is supported from the back side with a soft adhesive material. Key observations from these extensive modeling efforts have been discussed and the conclusions from the current study can serve as a general guideline to improve cover glass’s reliability of a handheld device.