Pan Pacific Symposium Conference Proceedings


Author: James C. P. McKeon
Company: Sonix, Inc.
Date Published: 2/10/2004   Conference: Pan Pacific Symposium

Abstract: As the feature sizes in microelectronic components continue to shrink, it becomes increasingly difficult to resolve the individual layers within the package. Typically, a higher frequency transducer is used to allow for increased depth resolution. However, in choosing a transducer for an application, it is critical to consider not only the frequency of the transducer, but the focal length as well. For it is necessary to have a long enough focal length so that when the ultrasonic beam is bent by the sample materials, the user can still focus on the interfaces of interest.

When UHF transducers are used, attenuation effects further complicate the situation. Since water attenuation effects increase exponentially with frequency, it is necessary to minimize the amount of water between the transducer and the sample surface (i.e. the water path) when doing UHF inspections. This means that the water path cannot always be adjusted to account for changes in material thickness, and a transducer with an appropriate focal length must be selected. In previous work it has been shown how Geometric Refraction Theory can be used to determine the appropriate transducer focal length and water path to inspect a particular interface within a package.

However, this work focused on transducer frequencies below the UHF level. When UHF frequencies are used, there is a discrepancy between the theoretically predicted and experimentally obtained values. In this paper, this issue is examined in detail for flip chip samples.

Keywords: SAM, microelectronics, transducers.

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