Scanning Acoustic Microscopy (SAM)

All FA Techniques

See Also:

Sectioning

SEM/TEM

Scanning Acoustic Microscopy (SAM) - Page 2 of 2

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Scanning acoustic microscopy has several modes. The A-scan mode is the real-time oscilloscope waveform of the acoustic signals based on the reflected echoes, or acoustic data collected at a single X-Y portion or point.

The B-scan mode is the cross-sectional display showing the ultrasonic reflection of the various interfaces along the depth of the package, or acoustic data collected along the X-Z plane at depth A. A B-mode scan furnishes a two-dimensional (cross-sectional) description along a test line (Y).

The C-scan mode is the display of the image of reflected echoes at the focused plane of interest, or acoustical data collected along an X-Y plane at depth Z. A C-mode scan furnishes a two-dimensional (area) description at a particular depth (Z) (see Figure 2). Usually the B-scan images are based on the C-scan image for precise determination of the depth of flaws detected.

Figure 2. Examples of C-SAM Photos;

red areas denote full delamination while yellow

areas denote slight delamination

When performing Scanning Acoustic Microscopy, the following must be observed :

1) The units must be placed in the sample holder such that their upper surfaces are parallel to the scanning plane of the acoustic transducer. Air bubbles must be swept away from the unit surfaces and from the bottom of the transducer head.

2) The transducer with the highest center frequency that still provides sufficient signal-to-noise ratio for good imaging must be selected. The transducer must be normal to the plane of the sample and the scan path must be parallel to the plane of the stage.

Failure Mechanisms/Attributes Tested For: Plastic-to-Leadframe Delamination, Plastic-to-Die Delamination, Plastic-to-Die Attach Delamination, Die Attach Voids, Internal Cracks, etc. Internal delaminations generally need to be addressed (especially those that occur on the die surface and bonding fingers) because they can lead to serious reliability issues such as neck breaks, heel breaks, and corrosion.

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