Pan Pacific Symposium Conference Proceedings


Authors: Janet E. Semmens and Lawrence W. Kessler
Company: Sonoscan, Inc.
Date Published: 1/31/2007   Conference: Pan Pacific Symposium

Abstract: Evaluation of flip chip devices for defects in the solder joint attach or underfill voids and delaminations using acoustic micro imaging (AMI) has become a matter of routine. However, the move presently is to utilize low-k dielectrics in the active layers on the chip surface. Low-k materials provide a significant increase in performance of the devices but the materials tend to be intrinsically porous and brittle. These properties can contribute to the creation of defects during the manufacturing process or in subsequent life cycle testing of the devices [1]. The properties of low-k dielectrics also contribute to challenges when evaluating the devices using AMI. The low-k materials have proved to be somewhat attenuating to high frequency ultrasound. When evaluating flip chip devices using AMI the ultrasound is introduced through the back side of the silicon chip to reach the inner chip surface and subsequent underfill and substrate levels. Even though the active layers on the surface of a silicon chip are very thin the attenuation must be taken into account when deciding what frequency to use for evaluation. Higher frequencies are preferable for analysis of the active layers. However, selecting for the active layers in the image can minimize the appearance of defects and characteristics of the underfill (which are below the active layers in a flip chip device) in some cases compromising the detection of the flaws. Recent studies have yielded experience in working with low-k dielectrics. Various AMI methods have been used to detect and distinguish defects in the active layers from voids and delaminations in the underfill and further efforts are focused on extracting more precise depth information within the active layers. This paper will present a brief background on AMI methods used for evaluation of flip chip devices with low-k dielectric and provide examples of analyses using AMI to detect internal features and defects in the devices. Keywords: Low-k dielectric, flip chips, Acoustic Micro Imaging (AMI)

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