4pEA8. Laser ultrasonic evaluation of solder connection in integrated chips.

Session: Thursday Afternoon, December 5

Time: 3:45

Author: Jerry Rosson Smith, Jr.
Location: Dept. Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332


Currently, no on-line techniques exist for the inspection of solder connections in surface mount technology (SMT) chips or in flip chips. This research investigated the use of laser-induced ultrasound in test chip samples to determine solder joint integrity. The ultrasonic vibrations were detected interferometrically and analyzed to determine chip mounting quality. Analysis was conducted in both the time and frequency domains. A controlled sample of flip chips, several (unidentified) of which were processed in a manner that tended to create poor connections, were tested and the vibrational signatures were compared. Comparison of the vibrational signatures showed a single flip chip with an abnormal signature. Detailed visual inspection demonstrated that the suspect chip was indeed poorly connected. Tests involving SMT consisted of obtaining the signatures of chips with high-quality connections. These connections were systematically damaged to simulate poor joints. Signatures were then taken from the newly damaged chips and compared with the undamaged signatures. Physical models and interpretations concerning experimental results have been developed. Future phases of research are outlined, including other promising results and capabilities. [Work supported by PRC.]

ASA 132nd meeting - Hawaii, December 1996