Increased demand for smaller electronics is driving the electronic packaging industry to develop smaller, more efficient component level packages. Surface mounted components, such as flip chips, ball grid arrays (BGAs), and chip-scale packages (CSPs), are being developed for use in high-volume production. All of these technologies use solder bumps to attach the active silicon to the substrate, and traditional nondestructive methods such as machine vision, acoustic microscopy or x-ray inspection cannot easily find solder bump defects.
Therefore, a system, consisting of an Nd:YAG laser that delivers pulses of infrared energy to the surface of the chip, a laser interferometer to record surface vibrations, and a high-speed data acquisition system to record the signals, was developed. The pulsed laser generates ultrasound on the chips surface, exciting the whole chip into a vibration motion, and the interferometer measures the vibration displacement of the chips surface at several points. Changes in the quality of the device or its attachment to the board produce changes in the free vibration response. Characterization of the differences between good devices and devices with defects, both in time domain and frequency domain, is performed using signal analysis.
The system has inspected flip chips and chip scale packages for missing and misaligned solder balls, but to characterize the resolution of the system for open solder joints, a study of the vibration modes excited by the laser source in a flip chip was performed on specimens with intentionally created defects. Experimental measurements of excited modes were compared with a modal analysis model created in ANSYS, and defects were detected as small changes in the mode shape on the surface of the chips.
Current inspection methods have also been inadequate for inspecting multi-layer ceramic capacitors (MLCCs). Flex cracks, caused by manufacturing processes, often cause the capacitors to fail in-service. Samples that have been cracked intentionally were compared with reference samples to determine the feasibility of using this technique to monitor the condition of MLCCs on an assembly line. Currently, there is no on-line inspection method for controlling this problem, but this technique was able to differentiate between good and damaged capacitors.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/6902 |
| Date | 15 April 2005 |
| Creators | Erdahl, Dathan S. (Dathan Shane) |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
| Format | 32687958 bytes, application/pdf |
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