Laser Ultrasonic Chip Inspection

This Small Business Innovation Research Phase I project will determine the feasibility of using advanced laser ultrasonic techniques for in-process inspection of epoxy underfill in flip chip and other high-performance surface mount packages. Epoxy underfill is used for strain relief and thermal conduction. Undetected voids in the underfill can cause local heating as well as disbonding of solder bumps. Laser ultrasonics is a technique for performing ultrasonic inspection using a pulsed laser to generate the ultrasound and a separate cw laser interferometer to detect the ultrasound at the point of interrogation. Laser ultrasonics offers several attractive features for the automated inspection of epoxy underfill: (1) its noncontact nature allows the inspection of parts without water immersion and during processing, (2) the capability of scanning allows the gathering of data at a high rate, (3) advanced, compensated receivers allow the interrogation of rough surfaces and (4) its high bandwidth provides high spatial and temporal resolution. Our approach during Phase I will be to optimize the laser generation and detection process, determine the best beam configuration and develop robust signal processing techniques. We will then build a laboratory breadboard for testing of samples provided by end users. In Phase II a prototype field inspection system will be developed and tested at an end user site.