SUMMARY

The long-term goal of this research is to assist in the development of a fast, accurate, and low-cost nondestructive inspection prototype system for solder joints in microchips. The goal of the work described in this thesis is to develop a fully automated focusing system that would reduce the testing time while maintaining or improving the quality of the defect detection results. The ability to perform the inspections in an automated manner is very important in order to demonstrate the ability of the system to be used for online inspection. To arrive at this goal, the development of a stand-alone autofocusing system was developed. By removing the need to manually focus the laser vibrometer, the inspection system will be able to be fully automated. The new autofocusing system was able to refocus onto the surface of a flip chip nearly five times faster than Polytec’s commercial system with a refocusing time of approximately 2.1 sec. When integrated into the non-destructive inspection system, the autofocus system was found to approximately reduce the testing time by half, while maintaining the same level of quality of results obtained by a skilled operator when manually focusing the vibrometer. Hardware was developed that retrofitted a vibrometer’s focusing head at the end of a fiber optic cable to a motorized linear stage. This stage controlled the standoff distance between the focusing head and the IC’s surface allowing for focusing to be achieved. Numerous tests were conducted to determine the optimal focusing parameters, which led to a refocusing time of approximately 2.1 sec. This time was found to be dependent on the surface finish of the IC being focused on. It was also found that to achieve optimal focusing, not only does the standoff height of the focusing head, which determines the laser spot size, need to be controlled, but also the exact location on which the laser is focusing.