SMTA International Conference Proceedings

Surface Flatness and Bond Thickness Measurement Methods Using The Acoustic Microscope

Author: Janet E. Semmens
Company: Sonoscan, Inc.
Date Published: 10/14/2012   Conference: SMTA International

Abstract: Acoustic micro imaging has been used in the microelectronics industry for years to evaluate the quality of devices by imaging the internal structures and/or defects in the devices. Lately methods have been developed to investigate other properties of the samples such as the flatness/warpage of devices, substrates, or wafers, and to measure the bondline thickness for die attach or thermal interface materials.

AMI (Acoustic Micro Imaging) is a non-destructive test method that utilizes high frequency ultrasound in the range of 5 MHz to 500 MHz [1]. Ultrasound is sensitive to variations in the elastic properties of materials and is particularly sensitive to locating air gaps (delaminations, cracks and voids). AMI typically involves producing images at specific depths in a device based on the location of reflected ultrasound echoes from the internal interfaces. The initial echo information is presented in the A-scan which represents a single point depth profile in the part. The time difference between the echoes corresponds to the depths within the device. The echo of interest is selected using an electronic gate and an x, y plot of the echoes for that selected depth (z) is produced. The shape and amplitude of the echoes at the interface give the condition at the interface. However, the information contained in the A-scan can also be used for other types of analyses. The distance of the surface echo from the sample relative to the transducer can be used to measure the flatness of the sample surface. Internal to the device the distance between echoes can be used for thickness measurements.

This paper will discuss the acoustic surface flatness (ASF) and bondline thickness measurement methods as well as present examples of these applications.

Key Words: 

Acoustic Micro Imaging (AMI), Warpage Measurement, Bondline Thickness

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