Scanning Acoustic Microscopy (SAM)

Scanning Acoustic Microscopy (SAM) is a failure analysis technique used for detecting disbonds or delaminations between package interfaces, e.g., interfaces between the plastic resin package material, the die, the die paddle, the leadframe, the die attach material, etc.

It basically consists of sending a sound wave through the package, and interpreting the interaction of the sound wave with the package. A typical scanning acoustic microscope (see Figure 1) may employ either pulse echo or through transmission inspection to scan for disbonds or delaminations. Pulse echo inspection consists of interpreting echos sent back by the package while through transmission inspection consists of interpreting the sound wave at the other end of the package, after it has passed through the latter. The ultrasonic wave frequency used ranges from 5 to 150 MHz.

Figure 1. Example of a Scanning Acoustic Microscope

The sound wave may be generated by a piezoelectric crystal, or transducer, that has been cut to provide a specific frequency. It is activated by a high voltage pulse from a transmitter, which is also known as the pulser. The activation would cause the transducer to vibrate at the specified frequency, which transmits an ultrasonic wave through the package.

This wave travels to the specimen through a medium or couplant, which is usually deionized water since sound waves could not travel through air at the frequencies used. The wave travels through the specimen's material at the material's velocity, with a portion of it being reflected back everytime it hits an interface within the material.

In the pulse echo method, the same transducer is used as sender and receiver of the sound waves. Pulses are repeated using repetition rates at which the echoes from one pulse will not interfere with those of another, e.g., 10-20 KHz. The echoes received by the transducer are converted to voltages, amplified, digitized, and presented to the user as an image.

In the through transmission technique, separate transducers are used to send and receive sound waves, both of which are on opposite sides of the specimen. The absence and presence of signals mean bad and good bonding, respectively.

<Proceed to Page 2 - Modes of SAM Operation>

FA Lab Equipment; Basic FA Flows; Package Failures; Die Failures

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